Ethiopian airliner down in Africa

[PJ2]

https://leehamnews.com/2019/04/05/bjorns-corner-et302-crash-report-the-first-analysis/#more-29839

Thinks that the force when electric tirm/ MCAS was switched back on probably bounced the crew out of their seats, causing them to lose/ weaken grip on the controls

While the gee is slightly less than 0g, the arms may fly up momentarily, but the crew would be belted-in, perhaps with the shoulder-straps still on, (though they may have been removed for greater mobility). "Hitting the ceiling"? Hm.

[spornrad]

In the prelim. report is a clear statement by the FO that the manual trim attempt did not work as advertised in the AD.
There is also a subtle hint that probably shows why the pilots in a last desperate attempt did reengage the trim motors, and how the pilots were desperately trying to follow the AD and manually resetting the trim, which was most likely aerodynamically blocked:
After the cutout, there is a very slow, long, subtle nose-down movement of the fin according to the report. What do you do when the crank is blocked, instinctively? You're rattling it! And then in this phase it moves only a few hairs nose-down, but not a bit Nose-Up.
Then, in desperation, they probably switched on the electric motors again, only to find out now, with two very short trim-up switch attempts, that in the meantime, electric trim quit working too (speed has meanwhile increased further). A nightmare.

This last attempt to implement the AD has now reset MCAS. And then comes design-wise (but is not in the FCOM or the AD, was never mentioned in training), while they still think about what to do next, after 5 s the final death blow of MCAS ...

The plane systems (MCAS and Trim) and the AD procedure just did not give them a fair chance IMHO.

An excellent overview over these 60 year old speed issues with the 737 trim system can be found in many old manuals and here: https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-range.html

[wheelsright]

(From an ex hardware/software tech writer) - a comment about software rather than aeronautics. If the timeline story (CVR derived) in comparison to the FDR traces is accurate, here is something weird from the preliminary report's data nobody has commented on.

The third MCAS activation lasting 9 or so seconds starting at 05:40:41 did not alter stab pitch trim because the FO had just cut power to the stabilizer jackscrew motor. The report glibly notes that fact. But why did MCAS even try to activate, as if sitting there fat, dumb and stupid? Exactly what type of coding allows the FCC to attempt to command AND trim when both STAB TRIM switches are already set to CUTOUT? Seems the designed use case never anticipated this sequence.

So it appears that this bolted on chunk of MAX-only software was not monitoring real-time trim motor electrics. Hell no, you cannot do that - a loom change might be required and that would disturb the production line and possibly delay certification! Or better yet, a few lines of more rigorous code were required.

Way up in the thread at least 2 incredulous posters suggested, sarcastically I think, that an intern might have programmed MCAS_1? Makes you wonder.

I agree, but this anomaly is only part of the story. There is also the question of why there are so few electric trim corrections considering the circumstances? MCAS has massive authority despite massive AoA disagreement. Surely, the obvious solution is for MCAS to be automatically disabled but not electric trim? Why would the engineers even contemplated MCAS continuing to operate with significant AoA disagree? What is the effect of a constant input on the pickle switch? Does it give continuous control authority or intermittent authority?

It is fairly obvious that the automated system should have disabled MCAS authority as soon as there was significant disagreement with the two AoA sensors. Blaming the pilots is not sufficient, the more fundamental defect is plainly a Boeing issue and seemingly inexcusable. I feel that the pilots needed to act within the first 15 or 20 seconds of stick shaker but failed to recognize the issue quickly enough. The question is how many crews would have acted quickly enough and why should they have to react at all? It is all so unnecessary.

It is suggested that Boeing provided the MCAS system to overcome approval considerations. However, it does not make sense to leave it to the pilots to disable MCAS when it could be handled automatically. Neither does it make any sense to disable electric trim completely in order to disable MCAS.

...Just touching the surface of the negligent design and certification issues...

[42go]

DaveReidUK
"The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope."

I assume from your post that you understand what this gobbledygook means? Can you explain it in English?

[fizz57]

...
Those are the official excuses. I don't buy them. It was honestly a very reasonable system when safety was important but not as important as today, data buses did not exist and pilots came from the military.
...


They're not "official excuses". The dual redundant system has been thoroughly analysed and its consequences known and calculated to a nicety.

What you're proposing is a hybrid system (disabling an input to a good system in case of a single failure on the other system) which will have its own consequences.

There is a solution, as has been implemented in FBW aircraft - if you are going to patch FBW onto a dinosaur, then its sensor suite must also be upgraded to meet those requirements and not rely on more patching to a grandfathered certification.

[sycamore]

From what I`ve read ,the MCAS operates when flaps are `UP`...What is the flap limiting speed,and does the system(MCAS) depend on the flap lever position only...?
I used to fly C-130,which had power controls,but power to the rudderboost was limited when the flaps were UP,but full hydraulic power beyond 20 deg,primarily to prevent overstressing the fin at `high speed`,but cover the lower speed asymmetric case requiring more rudder...
However,if one was doing `tactical/fighter affiliation/more aggressive flying,one could `cheat` by pulling a c/b for the FLAP hydraulics,and then select the flap lever to 20 deg.This then gave the rudder full hyd.,but the flaps were still `UP`..

I would have thought that the immediate actions drill would have also stated to have reduced speed to perhaps below 300 kts..

[Chesty Morgan]

Chesty, we discussed this earlier, and you said you have flown the 737 with manual trim and it was no problem.
I’ve only tried this a few times, but found the manual trim to be pretty hard. A friend of mine got «Stab out of trim» enroute and diverted because he thought he had a jammed stab. This after he tried manual trim and found it so hard he concluded he had a jammed stab.
It now looks like manual trim is nearly impossible at higher speeds.
It puzzels me a bit that the stab can be trimmed so far it will bring the aircraft out of the pilot’s control. And then you can’t manually bring it back under control because the trim forces are too high.

How Boeing will solve this is beyond me. MCAS is a killer and if they restrict it it will affect the certification. In order to get rid of MCAS they have to redesign the aircraft.
IMHO the MAX will stay on ground for a long time.

Yes but that's a function of aerodynamic load.

My point was that anyone can turn a wheel regardless of hours (obviously if it's not prevented by aerodynamic load) so to suggest that the FO couldn't turn it because he had only 200 hours was and is total nonsense (and I know you didn't make that point).

[DaveReidUK]

DaveReidUK
"The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope."

I assume from your post that you understand what this gobbledygook means? Can you explain it in English?

Nope, sorry, you assume incorrectly - I don't speak gobbledygook either. You would need to ask EASA.

I think that a rough translation is "when electric trim runs out, pray you have enough time, strength and altitude left to start winding ..."

[yanrair]

Is that what it is?...250 turns of the trim wheel from stop to stop? That info wasn't available anywhere in the AMM, the FCOM or even the FCTM. Like some, I wondered how many turns it was, so thanks.

The full range (from the AMM) of the stab is 17°. This range is not available to all controls, (electric, manual, wheel), as noted in this thread, but let us assume the available range is -1 AND to 16 ANU using the big wheel.

Now we can calculate turns and degrees of trim, (remembering the comments on the difficulty of turning the wheel under some circumstances).

250 turns / 17 degrees = 14.7 turns per degree, or,
17 degrees / 250 turns = 0.07° per turn.

If the thinking and the math is correct, we can see that there is a lot of work and time to manually modify the stab trim using the wheel. In fact, those who fly/flew the B727/B737 will recall just how fast the wheel goes around when electrically-trimming in normal flight, flaps-up; the white mark on the wheel is almost a blur...

PJ2
having done manual trim on 707-737:-800 during sim training and air test over thirty years - a few points
1 stop wheel turning before you get way out of trim is the drill. But you have to notice. I note in the video posted here it took 10 seconds to disable STAB. Lion air struggled for 10 ?? minutes. In other words STAB is off so quickly that all these situations we speak of here don’t occur. And if they do, go to next step >>
2 old trick as mentioned earlier- off load stab by releasing back pressure for a few seconds allows you to trim ANU in any load situation . Both pilots both wheels with handles extended. Very quick. It’s the elevator loads against the STAB jackscrew that causes the high loads . But you have to know this and I think it’s not taught any more.
3 Stab is three times more powerful than elevators - they don’t ‘blow back’- just not designed to overcome STAB.
4 if you’ve turned off STAB ELECTRICS you can turn them on to enable ANU trim. Thumb switches. Then when back in green range - safe range- STAB OFF and trim manually.

5 But- and this all gets back to training- you have to know all this. Not look in manuals. It has to be in the core of your airplane skill base. Trained by the trainers. And if the trainers don’t have it ........
Summary. Are pilots new to 737 aware of the dangers posed by the stabiliser?
They do runaway stab, jammed stab and manual reversion during type rating training- at least did until recently! So they know how tough an animal the STAN can be but manageable.
MCAS
So. MCAS being sorted. Good thing. Does that leave us still with a much bigger problem? The elephant in the room! What’s going to happen next time an automated function badly misbehaves- and it will.
Y

[Alpine Flyer]

Is that what it is?...250 turns of the trim wheel from stop to stop? That info wasn't available anywhere in the AMM, the FCOM or even the FCTM. Like some, I wondered how many turns it was, so thanks.

Having been on the jumpiest of a classic or NG (never been in a MAX), those trim wheels seemed to turn quite a lot even for very short bursts of trim input, so 250 is quite credible.

[73qanda]

5 But- and this all gets back to training- you have to know all this. Not look in manuals. It has to be in the core of your airplane skill base. Trained by the trainers. And if the trainers don’t have it ........
Years and years of drift towards ‘lean operations’ where training gets faster and shallower and faster and shallower as the decades slide by.
Why keep 10 sim sessions for a type rating when you can get away with 9 and collect a $10,000 KPI bonus?
Two years later........ why keep 9 sim sessions for a type rating when you can get away with 8 and collect a $15,000 KPI bonus?
Two years later.........why do 8 full flight sim sessions for a type rating when you can get away with 6 + 2 cheaper ‘motion off’ sessions and collect a $20,000 KPI bonus?

[lancs]

Aviate, navigate, communicate?

[yanrair]

In the prelim. report is a clear statement by the FO that the manual trim attempt did not work as advertised in the AD.
There is also a subtle hint that probably shows why the pilots in a last desperate attempt did reengage the trim motors, and how the pilots were desperately trying to follow the AD and manually resetting the trim, which was most likely aerodynamically blocked:
After the cutout, there is a very slow, long, subtle nose-down movement of the fin according to the report. What do you do when the crank is blocked, instinctively? You're rattling it! And then in this phase it moves only a few hairs nose-down, but not a bit Nose-Up.
Then, in desperation, they probably switched on the electric motors again, only to find out now, with two very short trim-up switch attempts, that in the meantime, electric trim quit working too (speed has meanwhile increased further). A nightmare.

This last attempt to implement the AD has now reset MCAS. And then comes design-wise (but is not in the FCOM or the AD, was never mentioned in training), while they still think about what to do next, after 5 s the final death blow of MCAS ...

The plane systems (MCAS and Trim) and the AD procedure just did not give them a fair chance IMHO.

An excellent overview over these 60 year old speed issues with the 737 trim system can be found in many old manuals and here: https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-range.html
excellent article with diagrams- all thanks to Peter Lemme. It’s a pity that level of schematic is not easily available to lone pilots.

[PJ2]

Yanrair, all 5 points well-worth reading and memorizing. Thank you for a fellow aviator's recollections from those days - they remain as valuable and potentially life-saving as ever. I don't know what happened to them in the last two or three decades but there weren't too many wheels left that needed re-inventing, yet here we are. Another guy worth reading, just like Centaurus in Tech.

PJ2

[PJ2]

. . . so 250 is quite credible. Thanks, Alpine Flyer, yes, that seemed reasonable to me too.

[fdr]

Let one thing be clear, we now have facts.
The crew was extremely inexperienced :
The FO had grand total 361hrs of wich 207 the last 3 months.
The captain was 29 years. Had an impressive career!
Had 8122hrs total

July 23 2010 he graduated
FO 737-800 31 jan 2011
Then FO 757/767 777 and 787.
BUT!
And here comes the problem: In 26 Okt 2017 he made Cpt 737-800 , SO less then 1.5 years Command.
There is a total of 1477hrs 738 and 103hrs Max.
Of which a lot is FO time!!
So, a low timer indeed!

This is a warning on so many levels!


BLU, do we stop using captains that have less than 1.5 years in command?

[BluSdUp]

It looks like the FAA has decided to postpone the Certification of the Software update past April, according memo!

[BluSdUp]

No Max for RYR this summer schedule!
Summer in Ireland is April to end of October!

Max
RIP

[Rananim]

That said do disagree with statements on manual trim, pretty strong evidence that at the speed and trim they were in it would be physically very hard or impossible to trim manually without unloading maneuvers that the did not have the altitude for and/or knowledge/training of.
MurphywasRight
If the column forces were too high, one option (if you hadn't worked out how to engage the manual trim, which these guys hadn't) is to turn the trim back on, correct it with the normal electric trim switches, and then turn it off again before MCAS kicks back in. You asked what I would do, that's what I would do.
PaperHanger

They decide to cut out the trim switches at 0540:35, 35 seconds after first MCAS activation.N1 remains at 94% throughout leading to loss of speed control. But If ANU manual trim had been ordered immediately following cutout of stab trim switches, or better still, PF had trimmed back to 5 units(which has a visual marking on the trim index) and then disabled the trim switches,can we calculate if the aerodynamic loads were already too much for manual trim to work.What was the speed at 0540:35?
Captain asks if trim is functional at 0541:46,so that's 71 seconds after trim cutout where no attempt is made to relieve control forces and speed is allowed to build.

[threemiles]

Nope, sorry, you assume incorrectly - I don't speak gobbledygook either. You would need to ask EASA.

I think that a rough translation is "when electric trim runs out, pray you have enough time, strength and altitude left to start winding ..."

This is a master piece of an aviation agency output. Could be any, this is not sepcific to EASA: It is the result of lawyers writing tech statements or manuals. The 737MAX emergency AD is no better. It is contradictary, leaves open questions and is not the smart wording standard other industries have reached in the past 40 years, partially because of tough consumer laws.
The peak is the FAA "Continued Airworthiness Notification to the International Community" dated March 12, a document type that was non existant before this date, is not based on ICAO rules and had just one obvious purpose. CMA.

Too often I sit in front of aviation regulations, rulings and manuals and think: damn sh.., what is it they want to tell me? And the obvious questions that every semi-intelligent guy/gal would have from a paragraph are never raised in the document nor answered. Still in this modern world people are too often ashamed to ask the obvious. There is no shame if it can save lifes.
Commercial aviation is stuck in the late 60s.
It is the answer to thick pants mentality and low management quality; as long as knee-jerk reactions dictate it will never change.
I have been there. For more than 30 years and unsuccessful to change that.

[MemberBerry]

DaveReidUK


I assume from your post that you understand what this gobbledygook means? Can you explain it in English?

Maybe I can try, EASA's sentence was: "The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope."

This seems to be in reference to the thumb switches not being able to trim the stabilizer until the mechanical stop limit.

They seem to mean that the safety added by not being able to trim with the thumb switches until you hit the mechanical stops compensates not being able to do that when you actually need it.

For example, if a thumb switch gets stuck, the resulting runaway won't be able to bring the trim to the full nose down mechanical limit, so it decreases the risk of getting the aircraft in an unrecoverable dive, they consider that an advantage.

The disadvantage is that, if you really need to bring the trim full nose down, to the mechanical limit, you won't be able to do that with the thumb switches.

So they are saying the advantages and disadvantages compensate each other.

Also, a lot of people seem to interpret those EASA's statements as saying you are not able to use the thumb switches at all in those conditions. But the trim limit switches are designed to prevent you from reaching the mechanical limits, not going away from them, so electric trim attempts going in the opposite direction, away from the mechanical limit, should still work, even if you are outside the designed trim limits for manual electric trim.

So I think it's unlikely the trim limit switches were a factor in this accident.

[fgrieu]

For reference
- preliminary report on EA302 (https://games-cdn.washingtonpost.com/notes/prod/default/documents/6375a995-4d9f-4543-bc1e-12666dfe2869/note/4cb6f748-a0c0-45c2-bf0b-f672ba3cfebe.pdf) (source: Washington Post)
and pristine extracts of images in appendix 1 (improving on these in post 3161 (https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa-159.html#post10438895))
- preliminary FDR data (https://i.stack.imgur.com/ZNXRM.png)
- general overview of the flight (https://i.stack.imgur.com/Gxoxg.png)

[BluSdUp]

FDR
NO No, we have all been there!
I am just stating a FACT.
This Young Commander was experienced , just not as a Commander.

And according to Ethiopian propaganda he did all correct.
NO he did not!!
Engage AP at 400 feet with the stick shaker going : WRONG
Never controlling PWR and Speed WRONG
Retracting Flaps as per standard Ops when possible in a stall : WRONG
I feel so bad for him!

But sad to say, he was set up by Murphy, FAA and Boeing and I see only panic in the action and reaction.
After 4000+ hrs in 4 sims I have seen a bit, and it is all down to a confusing flight deck with this fail mode!
Something like this I have never encountered in a Sim

But , please
Were do You see experience? . Sorry to be so blunt.

Sincerely
Cpt B

[bsieker]

Then, in desperation, they probably switched on the electric motors again, only to find out now, with two very short trim-up switch attempts, that in the meantime, electric trim quit working too (speed has meanwhile increased further). A nightmare.

If you look carefully at the FDR traces it seems to me that the electric trim did in fact work after apparently re-enabling it. The line goes up ever so slightly around 5:43:15, just before MCAS trims nose-down again. About back to where it was when the trim cutout switches were set to cutout.

I wonder, since the next page (27) has much higher-resolution graphs of some parameters, why the graph showing the flight control parameters (p. 26) is only low-resolution (looks like a screenshot).

The scenario painted on Bjorn's corner at Leeham News (https://leehamnews.com/2019/04/05/bjorns-corner-et302-crash-report-the-first-analysis/) seems very plausible and extremely scary, especially the take on why only short trim blips were used. One of the most scary parts is that even at a moderately out-of-trim situation, where the PF could hold the control column forces for several minutes, that mechanical trim would not work, if that turns out to be true.

Bernd

[fdr]

So. MCAS being sorted. Good thing. Does that leave us still with a much bigger problem? The elephant in the room! What’s going to happen next time an automated function badly misbehaves- and it will.
Y


Having done reversion testing, I was wondering what I had missed in the wording, so have dusted off the manual and had another look at the FCTM wording for the runaway stabiliser and the follow on manual trim. In the latter it mentions excessive airloads, and then discusses having both pilots applying effort to the system....in extreme cases airloads have to be relieved, and the next sentence covers returning the aircraft to the actual in-trim speed while attempting to trim using the manual trim wheels.

... the problem with the wording is that having the aircraft now trimmed to an undesired speed (....Mach 2 etc from the runaway trim case...) then the crew are to match the trim case while using both pilots if needed to manually change the trim. So, the crew bunt over to match the in trim speed for the nose down runaway case... which is all well and good except that is generally where planet earth is also located. If you are in an A-10, that is possibly second nature, or if you are current on Stukas, but for an RPT aircraft, that seems to be rather light on reasonableness. If this is reasonable, then perhaps the OEM should load up one of their aircraft with the management and DERs involved, and go demonstrate the technique at low level and high speed and determine how reasonable that is in the real world where the crew are confronted with an unexpected surprise in close proximity to the ground or water. On second thought, it would appear unfair to ask the OEM to do that... or anyone else for that matter, pilots, cabin crew and passengers.

The 737 is the worlds most prolific jet transport, by a sizeable margin, the manner that the trim issue is worded, and the limited protection that exists with the Part 25 wording for compliance doesn't seem to be impressive, particularly for a design where current activity is making "a safe aircraft safer". Perhaps runaway trims just don't happen and there is no risk from the underlying design, but I'm pretty sure that the last person who tried to pass an FAA check ride with two pilots having all hands on the controls at the same time ended up with more than just a discussion item.

25.255 provides for a 3 second trim error to be introduced... that is not what either of the recent crews experienced. Perhaps 3 seconds is perfectly fine as a value, in which case, the crew just need the chicken entrails to know when the system may exceed 3 seconds of uncommanded motion.

Humans are adept at adaptation, we can find workarounds for almost anything, but some 50 years on, if the cure for the system is as described, it may be time to look closely at grandfather rights vs public safety. Boeing builds a good plane, however perhaps it deserves some more thought into the system architecture, and at the very least some reinforcement training for crews that may need to deal with the issues related to the design.

[zzuf]

Maybe I can try, EASA's sentence was: "The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope."

This seems to be in reference to the thumb switches not being able to trim the stabilizer until the mechanical stop limit.

They seem to mean that the safety added by not being able to trim with the thumb switches until you hit the mechanical stops compensates not being able to do that when you actually need it.

For example, if a thumb switch gets stuck, the resulting runaway won't be able to bring the trim to the full nose down mechanical limit, so it decreases the risk of getting the aircraft in an unrecoverable dive, they consider that an advantage.

The disadvantage is that, if you really need to bring the trim full nose down, to the mechanical limit, you won't be able to do that with the thumb switches.

So they are saying the advantages and disadvantages compensate each other.

Also, a lot of people seem to interpret that EASA's statements as saying you are not able to use the thumb switches at all in those conditions. But the trim limit switches are designed to prevent you from reaching the mechanical limits, not going away from them, so electric trim attempts going in the opposite direction, away from the mechanical limit, should still work, even if you are outside the designed trim limits for manual electric trim.

So I think it's unlikely the trim limit switches were a factor in this accident.

My take would be that the aircraft could not comply with the 3 second trim operation, no load, required for electric trims for (CS 25.255(a)(1)).
So they declared that the manual trim wheel was the "main trim'. This only requires a 30 lbf mistrim, but allowed trimming throught the entire flight envelope.
The electric stops were then reset so maximum electric trim deflection was sufficient for the "normal airline operational" envelope, manual trim picks up the rest.
So now we can claim how conservative we are.
Now, where does a stability augmentation system failure morph into a trim runaway?

[Rob21]

Is that what it is?...250 turns of the trim wheel from stop to stop? That info wasn't available anywhere in the AMM, the FCOM or even the FCTM. Like some, I wondered how many turns it was, so thanks.

The full range (from the AMM) of the stab is 17°. This range is not available to all controls, (electric, manual, wheel), as noted in this thread, but let us assume the available range is -1 AND to 16 ANU using the big wheel.

Now we can calculate turns and degrees of trim, (remembering the comments on the difficulty of turning the wheel under some circumstances).

250 turns / 17 degrees = 14.7 turns per degree, or,
17 degrees / 250 turns = 0.07° per turn.

If the thinking and the math is correct, we can see that there is a lot of work and time to manually modify the stab trim using the wheel. In fact, those who fly/flew the B727/B737 will recall just how fast the wheel goes around when electrically-trimming in normal flight, flaps-up; the white mark on the wheel is almost a blur...

PJ2
Do you know how many hand inputs from the pilot will take to complete one turn? Three, four? Supposing the answer is three, the pilot will have to make 44 hand movements to change one degree. If the pilot is able to execute one turn in 4 seconds (fast), a change of only one degree will take 59 seconds, or one degree per minute.
Not enough time to recover from a dive. If my math is correct, the only way to counteract MCAS input is with electric trim. But if you need to cut off trim motors to "kill" MCAS, how the pilot will manually turn the trim wheel to achieve enough amplitude to cancel MCAS inputs?

[42go]

MemberBerry
They seem to mean that the safety added by not being able to trim with the thumb switches until you hit the mechanical stops compensates the not being able to do that when you actually need it.

I'm sorry, but you and DRUK obviously do have a Masters in gobbledygook. DRUK says it "Might be a good time to reiterate the relevant part from the document:" - WHY I ask? Does he/she understand it? What is 'relevant'?

You 'explain' it in a way I do not, as a native English speaker, begin to understand.

What chance an Ethiopian or Indonesian pilot?

[Luc Lion]

Not too important, but there are 2 typos in the interim report which already misguided 2 pprune posters.
By comparing the report text with the DFDR diagram, it is obvious that these are typos.
They may be caused by a translation from Amharic to English ?

So please read:
...
At 05:39:22 and about 1,000 feet the left autopilot (AP) was engaged (it disengaged about 33 seconds later), the flaps gear was retracted and the pitch trim position decreased to 4.6 units.
...
At 05:40:12, approximately three seconds after AND stabilizer motion ends, electric trim (from pilot activated switches on the yoke) in the Aircraft nose up (ANU) direction is recorded on the DFDR and the stabilizer moved in the ANU direction to 2.4 units. The Aircraft pitch attitude remained about the same as the back pressure on the column increased decreased.
...

[bsieker]

Do you know how many hand inputs from the pilot will take to complete one turn? Three, four?

That's why the trim wheel has a flip-out handle, so you can crank it quickly: See also The video, around 14:05:

Mentour Pilot's video.

Looking at that, I'd say at least at low loads one can do two to three turns per second.

Bernd

[MemberBerry]

MemberBerry


I'm sorry, but you and DRUK obviously do have a Masters in gobbledygook. DRUK says it "Might be a good time to reiterate the relevant part from the document:" - WHY I ask? Does he/she understand it? What is 'relevant'?

You 'explain' it in a way I do not, as a native English speaker, begin to understand.

What chance an Ethiopian or Indonesian pilot?

Sorry, I went through multiple revisions while composing that reply, and doing that resulted in some small grammar errors I didn't notice before posting it, like that not deleting an instance of "the", that was no longer needed after rephrasing it.

Without the needless "the", it reads: "They seem to mean that the safety added by not being able to trim with the thumb switches until you hit the mechanical stops compensates not being able to do that when you actually need it."

I fixed those errors more than an hour ago, unfortunately you somehow managed to reply to the version containing that grammar error after I already fixed it. If there are any more grammar errors in my post let me know, and I'll correct them.

I'm not a native English speaker and maybe I could have rephrased it better, I realize it could be hard to understand. That's why I then detailed what I mean by that.

I'll make another attempt, in case it's still not clear: They were saying that the designed electric limits, preventing you from reaching the mechanical limits using electric trim, have both advantages and disadvantages.

[DaveReidUK]

and pristine extracts of images in appendix 1 (improving on these in post 3161 (https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa-159.html#post10438895))
- preliminary FDR data (https://i.stack.imgur.com/ZNXRM.png)
- general overview of the flight (https://i.stack.imgur.com/Gxoxg.png)

See posts #3139 and #3147.

[fdr]

FDR
NO No, we have all been there!
I am just stating a FACT.
This Young Commander was experienced , just not as a Commander.

And according to Ethiopian propaganda he did all correct.
NO he did not!!
Engage AP at 400 feet with the stick shaker going : WRONG
Never controlling PWR and Speed WRONG
Retracting Flaps as per standard Ops when possible in a stall : WRONG
I feel so bad for him!

But sad to say, he was set up by Murphy, FAA and Boeing and I see only panic in the action and reaction.
After 4000+ hrs in 4 sims I have seen a bit, and it is all down to a confusing flight deck with this fail mode!
Something like this I have never encountered in a Sim

But , please
Were do You see experience? . Sorry to be so blunt.

Sincerely
Cpt B

BSU,

Before the big bang there is no experience, after the big bang there is experience. The individual chance of a critical system event occurring is unassociated with experience. The risk of a bird strike, engine failure, trim runaway is equally distributed across the career of the crew member. The recovery method suggested by the FCTM is apparently problematic given recent history, and the wording is hardly confidence inspiring. If the pilot was old enough to have had training that included the gems on this that are coming out now, then that is wonderful, and all would still be right in the world. Reading the FCTM alone would not necessarily result in competency in conducting the implied manoeuvre, one which assumes that there are two pilots in the seat at the time, and that sufficient altitude exists to recover the aircraft from the trim problem.

The more reflection on the recovery technique, the less it appears to be reasonable to be conducted, and at the very least the more necessity there is to undertake the training in the simulator. A yo-yo manoeuvre is not what one expects to be needed in a Part 25 transport, it is likely to spill the champagne in the front and to end up with a flight attendant shaped dent in the overhead lining down the back. The calendar indicates this is now 2019, and the FCTM suggests in rather vague terms a procedure that is essentially aerobatic, and Wilbur and Orville would have not been so happy with in 1903.

The design standard and the design is unlikely to be changed any time soon, but anyone considering that the crew of these two accidents were deficient in dealing with the trim condition needs to take a look in the mirror, and think seriously about the situation they were placed into. Post hoc, it is quite easy to say "I woudn't have done that" or "I would have done this", but I can say that I trained late in my jet career on the 73, under an FAA 142, and the implied procedure of the FCTM was not a takeaway, conceptually or in practice. Having flown some rather lousy designs where jack stall could occur, the concept in the unloading is not alien, but when the procedure calls for both pilots on the controls at the same time, and to undertake a ballistic flight path either upwards or downwards as determined by the in trim speed that has been established by the uncommanded motion, that just doesn't appear to gel with the spirit of RPT jet transport certification by the leaders of the worlds aerospace regulators.

The recovery technique that is implied in the FCTM, and which is not incorporated in the QRH as a recall item, is rather depressing, no matter how much lipstick is put on it.

In respect to the "errors" suggested to have occurred, the alternative observation is the pilot had ascertained that the stall warning was spurious, and therefore engaged the A/P, and retracted flaps. Perhaps he had a compelling reason to maintain speed, perhaps arising from the fact that the AOA outputs to the ADIRU and alters that sides IAS as a function of the sensed AOA, a refinement of the air data system... therefore having both AOA and IAS issues, the pilot elected to prudently maintain power to gain separation from the hard stuff. Perhaps. Equally as likely, under the assault of information and task demands that confronted the pilots, they were cognitively overloaded. Perhaps. Getting into a situation where you are leaving teeth marks on the elevators is never fun, and even less when there is a risk of catastrophic outcomes. The next crew to experience such conditions will have been gifted the insight that sober reflection on the situation that befell these crews. Whether the pilot had 1.5 years or 150 years is unlikely to be a factor in the outcome of the event, IMHO.

[StuntPilot]

"They seem to mean that the safety added by not being able to trim with the thumb switches until you hit the mechanical stops compensates not being able to do that when you actually need it."

Still gobbledygook to me.

How is safety added by not being able to trim with thumb switches? In particular, until a mechanical stop is hit? I would think it is the other way around, that hitting a mechanical stop disables trimming? Furthermore, I would think that a mechanical stop should never be hit, that there should be some microswitches on the actuator to prevent hitting a mechanical stop.

How does not being able to trim when a mechanical stop is NOT hit compensate not being able to do that when you actually need it?

[industry insider]

Could someone more knowledgeable than me kindly explain why there appear to be 2 references to Flap retraction as below, or am I misreading the report?

At 05:39:22 and about 1,000 feet the left autopilot (AP) was engaged (it disengaged about 33seconds later), the flaps were retracted and the pitch trim position decreased to 4.6 units.

and
At 05:39:45, Captain requested flaps up and First-Officeracknowledged. One second later, flap handlemoved from 5to 0 degrees and flaps retraction began.

Many thanks

[bsieker]

Could someone more knowledgeable than me kindly explain why there appear to be 2 references to Flap retraction as below, or am I misreading the report?



and


Many thanks

Luc Lion did here (https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa-167.html#post10439695). The first probably refers to gear retraction, or perhaps to partial flap retraction.

Bernd

[safetypee]

bsieker #3326, take care when interpreting the FDR trim. The switch position for ‘manual’ elect trim probably has a low sampling rate, thus a single data point would be displayed as a ramp up / down. The important aspect is that there is no change in the pitch trim position.

Thus the indications toward the end off the flight probably identifies reactivation of the elect trim, even two pulses recorded due to selecting the two switches back to an active state; either without further pilot elect trim input by choice, or due to a certification inhibit (? discussed elsewhere), or with manual elect trim, it was not strong enough to overpowered the tail forces (from the crew’s perception the latter situations were of an elect trim fail)
Thereafter, the trim command is only down - elect signal (MCAS), the actual trim position further nose down.

The other important aspect is that with the elect trim inhibited some time before, there was no change in trimmed position; i.e. the MCAS had no effect, but critically there was no nose-up trim from manual trim wheel operation, indicating the crew’s inability to move the trim.

[AfricanSkies]

Of course not, you simply turn the manual trim wheel.

About 250 revolutions from full ANU to full AND ...

Maybe in a 737, But it's wasn't in other jets, like the Fokkers. The trim wheel is just geared ..again question the 737 design..are so many clack clack clack turns necessary?

[MemberBerry]

Still gobbledygook to me.

How is safety added by not being able to trim with thumb switches? In particular, until a mechanical stop is hit? I would think it is the other way around, that hitting a mechanical stop disables trimming? Furthermore, I would think that a mechanical stop should never be hit, that there should be some microswitches on the actuator to prevent hitting a mechanical stop.

How does not being able to trim when a mechanical stop is NOT hit compensate not being able to do that when you actually need it?

Obviously hitting the mechanical limit disables trimming. It's a hard limit. But there are also electric switches preventing you from reaching the full nose down (and up) position using electric trim even before you hit the mechanical limit. Boeing regards this additional limitation as a safety feature. And indeed, in case of electric trim runaway, it can limit the amount of trim the runaway could apply, so it can improve safety in some situations.

Later edit:

You can read in more detail about that in the latest Satcom Guru article: https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-range.html

In that article there is a table describing the available ranges for the various types of electric trim, compared to manual trim with the trim wheels.

For example, for the 737-800, the full trim range available with the trim wheels is -0.20 to 16.9 units. For manual electric trim with the flaps retracted the range available is 3.95 units to 14.9 units, so far away from the mechanical stops.

That's what the EASA document was talking about. You can't access the full range of mechanical trim positions using manual electric trim. With the flaps retracted on the 737-800 you would only have access to a range of 10.95 units of trim out of the total range of 17.1 trim units available with the trim wheels.

Unfortunately MCAS doesn't use the same limits as manual electric trim, so it can bring the trim closer to the full nose down limit. In the Ethiopian flight it manages to bring it to 0.4 units of trim at some point.

[JesusonAHarley]

I usually don't contribute anything to a discussion, preferring to listen more to what everyone has to say. This is reflected in my posts on here too, which are non-existent. However, I have been following this thread very keenly and am very grateful to all the amazing insights and points of view provided. I'm a NG/Max driver and coincidentally, flew a Max on both the crash days.

Generally, my attitude towards any incident / accident is "They should have done this. But, I wasn't in that hot seat. Maybe I would've done the same". However, I've been struggling a lot trying to get that attitude and the posts on here have helped. Especially the ones which have been downright condescending of the operating crew. They have helped me get my perspective.

One thing that I have noticed in the preliminary report of the ET is that the pilot ANU stopped at exactly 2.3 units on three separate occasions. The first one was a shallow pick-up after the first MCAS activation. The second one was a more agressive pick-up immediately following the second MCAS activation, suggesting that the pilot(s) now knew what they were dealing with. As soon as the ANU stopped at 2.3 units, FO asked if he should cut-off the stab trim. The third was when they, presumably, reactivated the stab-trim to get some leverage with the electric trim and ended up with short bursts, instead of a long ANU activation.

With discounts given to adrenalin not allowing you to feel the AND for the first one and coincidence being the second, the third ANU also stopping at 2.3, suggests there was something else at play and not merely pilots not knowing how much to trim. The clue is provided in the timing of the FO suggestion for stab-trim cut-off.

Or am I reading too much?

[deltafox44]

BLU, do we stop using captains that have less than 1.5 years in command?
Also, do not let new type aircraft fly until they have made 15.000 flights :ugh:

[Luc Lion]

Could someone more knowledgeable than me kindly explain why there appear to be 2 references to Flap retraction as below, or am I misreading the report?
and
Many thanks
There are 2 typos in the report "History of Flight"
So please read:
...
At 05:39:22 and about 1,000 feet the left autopilot (AP) was engaged (it disengaged about 33 seconds later), the GEAR was retracted and the pitch trim position decreased to 4.6 units.

The DFDR diagram shows that it was indeed the gear retraction that happened at that time.

[b1lanc]

April, 4, 2019
We at Boeing are sorry for the lives lost in the recent 737 MAX accidents. These tragedies continue to weigh heavily on our hearts and minds, and we extend our sympathies to the loved ones of the passengers and crew on board Lion Air Flight 610 and Ethiopian Airlines Flight 302. All of us feel the immense gravity of these events across our company and recognize the devastation of the families and friends of the loved ones who perished.
The full details of what happened in the two accidents will be issued by the government authorities in the final reports, but, with the release of the preliminary report of the Ethiopian Airlines Flight 302 accident investigation, it’s apparent that in both flights the Maneuvering Characteristics Augmentation System, known as MCAS, activated in response to erroneous angle of attack information.
The history of our industry shows most accidents are caused by a chain of events. This again is the case here, and we know we can break one of those chain links in these two accidents. As pilots have told us, erroneous activation of the MCAS function can add to what is already a high workload environment. It’s our responsibility to eliminate this risk. We own it and we know how to do it.
From the days immediately following the Lion Air accident, we’ve had teams of our top engineers and technical experts working tirelessly in collaboration with the Federal Aviation Administration and our customers to finalize and implement a software update that will ensure accidents like that of Lion Air Flight 610 and Ethiopian Airlines Flight 302 never happen again.
We’re taking a comprehensive, disciplined approach, and taking the time, to get the software update right. We’re nearing completion and anticipate its certification and implementation on the 737 MAX fleet worldwide in the weeks ahead.
We regret the impact the grounding has had on our airline customers and their passengers.This update, along with the associated training and additional educational materials that pilots want in the wake of these accidents, will eliminate the possibility of unintended MCAS activation and prevent an MCAS-related accident from ever happening again.

Boeing: 737 MAX Update (http://www.boeing.com/commercial/737max/737-max-update.page)

[Luc Lion]

It was a great idea to have 2 cutout switches (up to the B737 NG) ; one acting on the yoke trim switches and the other acting on the autopilot and STS.
It was a not so great idea to replace them with a primary cutout switch and a backup cutout switch, both switches acting on both electrical channels of the trim.

[GarageYears]

Could someone more knowledgeable than me kindly explain why there appear to be 2 references to Flap retraction as below, or am I misreading the report?

Many thanks

The first is suspected to be a typo and should read "gear".

- GY

[TTail]

There are 2 typos in the report "History of Flight"
So please read:
...
At 05:39:22 and about 1,000 feet the left autopilot (AP) was engaged (it disengaged about 33 seconds later), the GEAR was retracted and the pitch trim position decreased to 4.6 units.

The DFDR diagram shows that it was indeed the gear retraction that happened at that time.
So the gear was raised at 1000'AGL? No doubt this crew was overwhelmed by the lights and shakers coming on....

[bsieker]

bsieker #3326, The important aspect is that there is no change in the pitch trim position.

Yes there is. The creep in the lines is too consistent for it to be random sampling errors (which are also there and clearly visible as jitter.)


Thus the indications toward the end off the flight probably identifies reactivation of the elect trim, even two pulses recorded due to selecting the two switches back to an active state; either without further pilot elect trim input by choice, or due to a certification inhibit (? discussed elsewhere), or with manual elect trim, it was not strong enough to overpowered the tail forces (from the crew’s perception the latter situations were of an elect trim fail)


True, these low-resolution traces need to be read very carefully, but I think a slight nose-up trim change is clear from the trace around the time the two manual trim switch inputs are recorded. Yes, we don't know the sampling frequency for pitch trim position, but as can be seen from the areas in the graph where it changes rapidly, it cannot be less than once per seconds, so that very very slow decrease from 5:30:45 to 5:43:10, and the following very slight increase between 5:43:10 and 5:43:20 are real. Both these movements are also mentioned in the textual part of the report.

The mention of failure of both electric and manual trim was much earlier, during the time where we assume that the cutout switches were in the cutout position. That to me is the most scary part that even for these moderate control column loads that can be held for several minutes, manual trim would not work at all. I had always assumed that in all but extreme out-of-trim situations, mechanical trim would be available.

Bernd

[Luc Lion]

So the gear was raised at 1000'AGL? No doubt this crew was overwhelmed by the lights and shakers coming on....
Sorry, confirmation bias ; I positively checked that it wasn't the flaps and then I misread another line for being the gear (was probably the AP).
So something was retracted, but it wasn't the flaps and probably not the gear.

[Rob21]

Thanks Bernd. But if, even with the wheel handle, the pilots can not turn the wheel fast enough? I understand that the elevator is the primary pitch control, but this is supposing the aircraft is trimmed accordingly. If, for some reason, the stabilizer does the opposite of what the pilot wants, the elevator becomes the secondary pitch control. An unwanted dive can only be corrected by using trim (on the 737). But with no electric trim it will take some precious time too bring the aircraft back to an atitude where the elevator is the primary pitch control again. And time was exactly what those pilots didn't have...

[bsieker]

Thanks Bernd. But if, even with the wheel handle, the pilots can not turn the wheel fast enough? I understand that the elevator is the primary pitch control, but this is supposing the aircraft is trimmed accordingly. If, for some reason, the stabilizer does the opposite of what the pilot wants, the elevator becomes the secondary pitch control. An unwanted dive can only be corrected by using trim (on the 737). But with no electric trim it will take some precious time too bring the aircraft back to an atitude where the elevator is the primary pitch control again. And time was exactly what those pilots didn't have...

The problem is not so much trim-wheel-motion speed (which I guess at light loads can be up to 5 revolutions per second), but that the sheer force required cannot be exerted by a human "without exceptional strength" if the aircraft is more than just a bit out of trim and nose-up control input needs to be held continuously because of low height above ground, which exacerbates the required force.

Bernd

[armchairpilot94116]

MCAS seems to be a cure that is much worse than the disease. And if you are having to resort to the manual trim you are really on a wing and a Prayer. Actually the prayer works better.

[deltafox44]

- After autopilot engagement, there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes; these oscillations also continued after the autopilot disengaged.So what is the significance or cause of this item in the report? Is this the result of the AoA sensor issue leading to the autopilot trying to track spurious inputs?

Or is it an unrelated problem, something else wrong?
I would think it's normal turbulence. The report lists everything happens, whether it may be a problem or not

[Avionista]

Having read most of the comments on this thread, my general conclusions are:

1. The crews flying JT610 and ET302 were reasonably well trained and experienced in flying B737 aircraft. Their flying skills could be characterised as representative of the "Average Pilot" within the total population of B737 type-rated pilots.
2. The MCAS system, as implemented on the B737 MAX, is extremely dangerous and should never have been certified on a passenger carrying aircraft. If it activates due to a sensor or system fault at the 'wrong' or disadvantageous moment during a flight, the aircraft can become unrecoverable.
3. Any automatic system that is permitted to control the horizontal stabiliser of a passenger aircraft should be required to have a fully redundant (triplicated) sensor/control system.

To make the B737 MAX safe/certifiable, the FAA and Boeing should consider the following steps:

1. Remove the MCAS system in its entirety.
2. To comply with FAR regulations concerning stick force as the aircraft approaches a stall AoA, Boeing should:
(a) consider aerodynamic changes to the airframe;or(b) develop a 'stick pusher' solution.

In addition to fixing the B737 MAX, Boeing should set their designers and engineers to work on building a completely new state-of-the-art replacement for the B737.

[positiverate20]

I usually don't contribute anything to a discussion, preferring to listen more to what everyone has to say. This is reflected in my posts on here too, which are non-existent. However, I have been following this thread very keenly and am very grateful to all the amazing insights and points of view provided. I'm a NG/Max driver and coincidentally, flew a Max on both the crash days.

Generally, my attitude towards any incident / accident is "They should have done this. But, I wasn't in that hot seat. Maybe I would've done the same". However, I've been struggling a lot trying to get that attitude and the posts on here have helped. Especially the ones which have been downright condescending of the operating crew. They have helped me get my perspective.

One thing that I have noticed in the preliminary report of the ET is that the pilot ANU stopped at exactly 2.3 units on three separate occasions. The first one was a shallow pick-up after the first MCAS activation. The second one was a more agressive pick-up immediately following the second MCAS activation, suggesting that the pilot(s) now knew what they were dealing with. As soon as the ANU stopped at 2.3 units, FO asked if he should cut-off the stab trim. The third was when they, presumably, reactivated the stab-trim to get some leverage with the electric trim and ended up with short bursts, instead of a long ANU activation.

With discounts given to adrenalin not allowing you to feel the AND for the first one and coincidence being the second, the third ANU also stopping at 2.3, suggests there was something else at play and not merely pilots not knowing how much to trim. The clue is provided in the timing of the FO suggestion for stab-trim cut-off.

Or am I reading too much?

I understand where you are coming from. I, too, was appalled at the attitude of some on here- stating the pilots must have been wrong based on where they came from. I also hypothesised a very similar scenario on 13th March- post 1171- all that I hadn't mentioned was the difficulty in turning the trim wheel at higher speeds, but I'd assumed that would be obvious if anyone looked at the indicated airspeed from the ADS-B data that was available at the time! (Put your hand out the window of your car when you're driving at 60mph/100kmh- it's a lot easier to move back and forward than at 100mph/160kmh!) The roller coaster movement I had never heard of before- and not sure if this would have been an option on this flight given the speeds and altitudes involved.

Mentour pilot's video was fantastic, it was uploaded prior to the publication of the preliminary report, it's a shame he has removed it. He also stated the reason for doing the test was because too many people instantly blamed the pilots just because of the geographic location of where they worked!

I also have a couple of queries about the data:

All the electric trim inputs from the pilot are short throughout apart from one...:

At 05:40:27 the Captain advised the First-Officer to trim up with him.

On this occasion, the trim moved 1.9 units ANU over a period of 8 or 9 seconds! This is the only occasion in the entire flight where the pilots were able to command ANU trim for any longer than 2-3 seconds. Possibly your point and my point are related to the 2.3 unit mark. Otherwise, is there some reason that the Captain's trim switches were compromised? It is the only time in the transcript where the Captain requested the FO to trim up with him. With the Captain's stick-shaker activated etc. would this possibly cause any complication to his trim commands being tripped out so soon each time? Is there another hidden 'safety' system that limits the pilot trimming up when stick-shaker is activated? Or is it simply just a case of the motor not being able to operate due to the increased forces at the given airspeed (when considering the blips later on)?

[PENKO]

BSU,

Before the big bang there is no experience, after the big bang there is experience. The individual chance of a critical system event occurring is unassociated with experience. The risk of a bird strike, engine failure, trim runaway is equally distributed across the career of the crew member. The recovery method suggested by the FCTM is apparently problematic given recent history, and the wording is hardly confidence inspiring. If the pilot was old enough to have had training that included the gems on this that are coming out now, then that is wonderful, and all would still be right in the world. Reading the FCTM alone would not necessarily result in competency in conducting the implied manoeuvre, one which assumes that there are two pilots in the seat at the time, and that sufficient altitude exists to recover the aircraft from the trim problem.

The more reflection on the recovery technique, the less it appears to be reasonable to be conducted, and at the very least the more necessity there is to undertake the training in the simulator. A yo-yo manoeuvre is not what one expects to be needed in a Part 25 transport, it is likely to spill the champagne in the front and to end up with a flight attendant shaped dent in the overhead lining down the back. The calendar indicates this is now 2019, and the FCTM suggests in rather vague terms a procedure that is essentially aerobatic, and Wilbur and Orville would have not been so happy with in 1903.

The design standard and the design is unlikely to be changed any time soon, but anyone considering that the crew of these two accidents were deficient in dealing with the trim condition needs to take a look in the mirror, and think seriously about the situation they were placed into. Post hoc, it is quite easy to say "I woudn't have done that" or "I would have done this", but I can say that I trained late in my jet career on the 73, under an FAA 142, and the implied procedure of the FCTM was not a takeaway, conceptually or in practice. Having flown some rather lousy designs where jack stall could occur, the concept in the unloading is not alien, but when the procedure calls for both pilots on the controls at the same time, and to undertake a ballistic flight path either upwards or downwards as determined by the in trim speed that has been established by the uncommanded motion, that just doesn't appear to gel with the spirit of RPT jet transport certification by the leaders of the worlds aerospace regulators.

The recovery technique that is implied in the FCTM, and which is not incorporated in the QRH as a recall item, is rather depressing, no matter how much lipstick is put on it.

In respect to the "errors" suggested to have occurred, the alternative observation is the pilot had ascertained that the stall warning was spurious, and therefore engaged the A/P, and retracted flaps. Perhaps he had a compelling reason to maintain speed, perhaps arising from the fact that the AOA outputs to the ADIRU and alters that sides IAS as a function of the sensed AOA, a refinement of the air data system... therefore having both AOA and IAS issues, the pilot elected to prudently maintain power to gain separation from the hard stuff. Perhaps. Equally as likely, under the assault of information and task demands that confronted the pilots, they were cognitively overloaded. Perhaps. Getting into a situation where you are leaving teeth marks on the elevators is never fun, and even less when there is a risk of catastrophic outcomes. The next crew to experience such conditions will have been gifted the insight that sober reflection on the situation that befell these crews. Whether the pilot had 1.5 years or 150 years is unlikely to be a factor in the outcome of the event, IMHO.
This sums it up nicely as far as I can judge. No matter the outcome of the investigation, the mere suggestion of the above scenario should send shivers through everyone's spine.

Regarding the thrust, whatever the reason they were still producing 94% thrust, may I add the sobering thought that reducing the thrust would have lowered the nose even further...

[GlueBall]

Besides having made time during the 6+ minutes of flight to navigate (setting and resetting altitudes/headings) and to communicate multiple times with ATC, it's hard to conceptualize how at low altitude in day VMC neither pilot had reacted to the obvious increasing cockpit noise from the rush of a air in the slipstream as the jet zoomed to 458 kts IAS and beyond clacker speed to 500 kts. The 29 year old captain's purported 8000 hours' experience level obviously lacked depth in situational awareness and manual control of the thrust levers.

[sgt18]

I am just a glider guy and frequent SLF, I am very surprised every time I read about the low number number of hours in these posts. My clubs insurance wanted to me to have 500 hours total time plus 250 hours tail wheel to fly a clapped out agwagon dragging gliders around. Do insurance companies not set standards in the airline world?

[infrequentflyer789]

Sorry, confirmation bias ; I positively checked that it wasn't the flaps and then I misread another line for being the gear (was probably the AP).
So something was retracted, but it wasn't the flaps and probably not the gear.

Autopilot engages, gear must be up for that to happen, no?

[deltafox44]

With the Captain's stick-shaker activated etc. would this possibly cause any complication to his trim commands being tripped out so soon each time? Is there another hidden 'safety' system that limits the pilot trimming up when stick-shaker is activated? Or is it simply just a case of the motor not being able to operate due to the increased forces at the given airspeed (when considering the blips later on)?
Would the trim motor not be able to move the stab, we would still see the trim command from the pilot.

The same when trim cutout switches were off, we don't see any change in stab position but we still see MCAS AND command

[deltafox44]

Originally Posted by jimjim1
I offer an explanation for the behaviour of the Left hand AoA indication throughout the flight.

If the vane had been lost the AoA sensor would become unbalanced about its usual axis or rotation. The internal balance weight** would then cause the axle to be subject to movement when the aircraft transitioned from +g to -g. +g would cause the indication of +AoA. (If I have got this the right way round
Excellent post, the tracking is almost too perfect to be believed at first.

This fits with the AoA heater fault as well, whatever happened caused 2 symptoms that are hard to explain except as physical damage to the sensor since the heater supply is independent of the resolver.

Someone commented that the pilots would have heard a bird strike, given the lack of a full CVR transcript we don't know if anything was audible.
I would suspect that the press conference statement of 'no foreign object' would suggest but not prove none was audible.

Anyone know if a departing vane by itself would cause a heater open?

One other observation is that the flight deck actions seem to be mostly normal until the AP disconnect, almost as though the stick shaker was activated but not working or noticed.
If missing from CVR that probably would have been noted.
Yes, a broken (losing its "winglet" part) or departing vane would explain AoA vs. gees curve and AoA heater fault.

If not a bird strike, it could be a previous damage which would have almost broken the vane. The AoA disagree happens when vertical acceleration is at its maximum (1,5 g or so) at the rotation. This acceleration would have finished to break the vane...

[bill fly]

The idea of offloading the stab by releasing elevator input began when jet upsets began to be better understood.
At the very high speeds reached, the stab could not be trimmed while max elevator input was being applied. I believe it was a group including Boeing and Airbus who issued the advice (no particular aircraft in focus) to release elevator pull and trim (gently) the stab before applying elevator input again.
Of course in the case of an upset the procedure was not expected to be applied at treetop height but further up.

[silverstrata]

Quick summary of events - please amend as necessary.
.

1. On take off, one of the AoA vanes is damaged.

2. 2 seconds after take off, stick shaker activates, resulting in understandable nose down pitch to gain speed.

3. Speed trim gives nose down trim inputs, as is usual - so trimmer is automatically trimming, as usual.

3. After flaps up MCAS becomes active, and gives large trim down - like a super speed-trim system.
... Pilots may think this is normal speed-trimming.
... (MCAS is using data from one sensor, which it should not be able to do.)

4. While sorting out the perceived stall situation, MCAS give two huge trim forward commands, half of which is wound back.
... (ending in a trim of 2.5 units, which is about 2.5 units more forward than usual)

5. Pilots are struggling with control, and turn off stab trim system. Some 50kg of force is needed to keep nose up.

6. If an attempt to engage autopilot was made it would be unsuccessful, as it cannot be engaged with stick pressure applied.

7. It is likely that manual trimming was attempted. But the manual trimmer will not work at these speeds and trim settings
... (the trimmer is jammed at 2.5 units, with full back elevator pressure applied.)

8. It is decided to reengage the electric trim system, so they can re-trim.

9. Trim system is reengaged, and two small trim-backs are made, to solve the out of trim situation.

10. But MCAS gives another huge dose of forward trim, wrenching the control column out of their hands, and pinning them to the roof.
... (it gives negative 0.5 g).

11. Control column is pulled full back, but cannot control the pitch, which continues to lower to -40 degrees.

12. Aircraft impacts ground.

.
Having tried this in the sim, I am surprised that full back pressure on the control column gave no response in pitch attitude. The sim did give a slow but positive response, although it took both pilots with maximum force to get a response and that response would be too slow in most circumstances. But on the real airplane, it looks like a stab-trim position of 1 unit at high speed renders the aircraft completely uncontrollable, and a crash inevitable. (They would understand that electric trim was faulty, and manual trim is not available at these trim settings.)

Silver

Edit: This was an NG sim, not a Max sim.....

[SteinarN]

Quick summary of events - please amend as necessary.

1. On take off, one of the AoA vanes is damaged.
2. 2 seconds after take off, stick shaker activates, resulting in understandable nose down pitch to gain speed.
3. Speed trim gives nose down trim inputs, as is usual - so trimmer is automatically trimming, as usual.
3. After flaps up MCAS becomes active, and gives large trim down - like a super speed-trim system.
Pilots may think this is normal speed-trimming.
(MCAS is using data from one sensor, which it should not be able to do.)
4. While sorting out the perceived stall situation, MCAS give two huge trim forward commands, half of which is wound back
(ending in a trim of 2.5 units, which is about 2.5 units more forward than usual)
5. Pilots are struggling with control, and turn off stab trim system. Some 50kg of force is needed to keep nose up.
6. If an attempt to engage autopilot was made it would be unsuccessful, as it cannot be engaged with stick pressure applied.
7. It is likely that manual trimming was attempted. But the manual trimmer will not work at these speeds and trim settings
(the trimmer is jammed at 2.5 units, with full back elevator pressure applied.)
8. It is decided to reengage the electric trim system, so they can re-trim.
9. Trim system is reengaged, and two small trim-backs are made, to solve the out of trim situation.
10. But MCAS gives another huge dose of forward trim, wrenching the control column out of their hands, and pinning them to the roof.
(it gives negative 0.5 g).
11. Control column is pulled full back, but cannot control the pitch, which continues to lower to -40 degrees.
12. Aircraft impacts ground.

Having tried this in the sim, I am surprised that full back pressure on the control column gave no response in pitch attitude. The sim did give a slow but positive response, although it took both pilots with maximum force to get a response and that response would be too slow in most circumstances. But on the real airplane, it looks like a stab-trim position of 1 unit at high speed renders the aircraft completely uncontrollable, and a crash inevitable. (They would understand that electric trim was faulty, and manual trim is not available at these trim settings.)

Silver
Maybe the sim isn't programmed with the elevator blow back effect?

[OldnGrounded]

It was a great idea to have 2 cutout switches (up to the B737 NG) ; one acting on the yoke trim switches and the other acting on the autopilot and STS.
It was a not so great idea to replace them with a primary cutout switch and a backup cutout switch, both switches acting on both electrical channels of the trim.

This^^^ (my emphasis). If the actual change to the trim switches didn't threaten the manufacturer's certification strategy, I wouldn't expect that doing the sane and sensible thing -- disabling HAL's electric trim authority (STS, AP and MCAS, together or separately) while leaving the pilots' alone -- would be a problem. So, why . . .?

[KRH270/12]

I usually don't contribute anything to a discussion, preferring to listen more to what everyone has to say. This is reflected in my posts on here too, which are non-existent. However, I have been following this thread very keenly and am very grateful to all the amazing insights and points of view provided. I'm a NG/Max driver and coincidentally, flew a Max on both the crash days.

Generally, my attitude towards any incident / accident is "They should have done this. But, I wasn't in that hot seat. Maybe I would've done the same". However, I've been struggling a lot trying to get that attitude and the posts on here have helped. Especially the ones which have been downright condescending of the operating crew. They have helped me get my perspective.

One thing that I have noticed in the preliminary report of the ET is that the pilot ANU stopped at exactly 2.3 units on three separate occasions. The first one was a shallow pick-up after the first MCAS activation. The second one was a more agressive pick-up immediately following the second MCAS activation, suggesting that the pilot(s) now knew what they were dealing with. As soon as the ANU stopped at 2.3 units, FO asked if he should cut-off the stab trim. The third was when they, presumably, reactivated the stab-trim to get some leverage with the electric trim and ended up with short bursts, instead of a long ANU activation.

With discounts given to adrenalin not allowing you to feel the AND for the first one and coincidence being the second, the third ANU also stopping at 2.3, suggests there was something else at play and not merely pilots not knowing how much to trim. The clue is provided in the timing of the FO suggestion for stab-trim cut-off.

Or am I reading too much?

This!

Why did they never really reastablished an „in trim condition“ using electric trim early in the flight?

Why did they not use longer trim bursts to counteract MCAS before engaging the cutout switches?

Why did they not trim up after disengaging the cutout switches?

Its really hard to believe they pullend the controll collum back about 2/3 from nutral with massive force the whole time without ever trying to consequently using stab trim to get back into an in trim condition....

[safetypee]

bisieker #3350, https://www.pprune.org/showpost.php?p=10439779&postcount=3350 (https://www.pprune.org/showpost.php?p=10439779&postcount=3350)

Bernd,
’ … had always assumed that in all but extreme out-of-trim situations, mechanical trim would be available.’

This is a very important point as it appears that the same assumption was in the EASA - Boeing case for equivalent safety as a means of compliance.
Boeing applied for a regulatory dispensation for the inability of the electric trim to achieve a trimmed condition throughout the aircraft’s speed envelope. Although this was unusual, but of importance that it was not described as a failure case, the use of manual trim was an acceptable alternative with caveats of training and normal procedure (not made available for 737 MAX ?).
Thus in normal operation, at all speeds, it should be possible keep the aircraft in trim, and able to correct small deviations (accel / deceleration), with the use of the manual trim wheel.

However, the abnormal situation where the aircraft is grossly out of trim (trim runaway) appears not to have been considered - or assumed to be the same as normal operation. This appears to be incorrect.
The difference in air-loads on the horizontal tail and elevator (https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-range.html) result in the inability of the trim wheel to overcome the forces and regain a trimmed state.

This situation was not posed in Boeing’s application, or it was assumed that FAA - EASA would consider it, possibly on the basis of similar approvals in NG (my assumption). Thus for trim runaways, the dispensation is insufficient to meet the regulatory requirements, but more important that there loss of all pitch control, trim and elevator effectiveness!

Either this represents a significant difference between the NG and MAX in the aerodynamics affecting the failure cases (likely), or that the NG is similarly non compliant in the failure case.
This could also question if Boeing actually tested the dispensation for the MAX in normal flight conditions - opposed to grandfathering it from the NG.
Also, to check that the abnormal NG procedures would still be effective in the MAX, again because of different aerodynamics (and apparently, without including the necessary procedures for recovery of a trimmed condition in the MAX manuals; the ‘roller coaster’ could not be flown).

These assumptions could leave some very big holes in the 737 MAX certification, not only being non compliant, but also un-flyable with some trim failures - where MCAS modification might only address one of them.

[Interflug]

Seems PERFECTLY reasonable, to me. They have expected US to do that (with passengers) ... they should first show us how it is done. (without passengers, of course)
Well, agreed, even though, as a passenger, I still would prefer that rollercoaster over hitting the ground with 500 mph. I those are the two choices left to us.
Maybe a new cabin announcement is in order: "In the unlikely event of a stab trim malfunction, the pilots will try to correct it with sudden rollercoaster movements. Please hold on to your dentures and glass eyes, and then help other passengers to not hit the ceiling."

[jan99]

Well, agreed, even though, as a passenger, I still would prefer that rollercoaster over hitting the ground with 500 mph. I those are the two choices left to us.
Maybe a new cabin announcement is in order: "In the unlikely event of a stab trim malfunction, the pilots will try to correct it with sudden rollercoaster movements. Please hold on to your dentures and glass eyes, and then help other passengers to not hit the ceiling."

Rolling the airplane on its back may be an interesting variation.

[Just This Once...]

I'm still struggling with the though that a grossly mis-trimmed stab on an NG cannot be recovered by either electric trim or by the strength of 1 or even 2 pilots cranking the wheels when the aircraft is at certain parts of the flight envelope.

As covered by others above, it seems bizarre to rely on having the airspace and time available to perform an acceleration or deceleration to a trimmable speed and/or perform a manoeuvre in the opposite sense to what you are trying to achieve in order to put the stab in a safe position.

Hopefully Boeing can enlighten us as to which parts of the performance envelop allow for PF solo cranking, PM dedicated cranking, both pilots cranking or just plain impossible to crank the wheel due to aerodynamic load. The NG is still flying and I am sure the AOCs would like to know, even if the FAA is asleep at the wheel at a benign 1G.

[RatherBeFlying]

At initial stick shaker, the aircraft can be expected to be in trim or not far from it. Better to head off MCAS at the pass than let it compound an already difficult situation to one where recovery is uncertain.

Electric Trim Availability?

It's been pointed out that the range allowed for electric trim is less than can be obtained from the trim wheel (airload permitting).

Does that mean electric trim can not be used to return trim outside its range back to within its range?

[hans brinker]

I think there is a reasonable consensus (lest's say 50% chances) that vane shaft broke, keeping AOA vane attached or not, and subsequent alarms and checklists (both useful and useless) threw the crew out of balance. They didn't manage airspeed and lost ability to trim. They reengaged electric trim, was not strong enough either, forgot to CUTOUT, mcas trimmed down, EOF.

I think one of the biggest problems here is the compounding of stupidities. Each stupidity on its own is very much survivable, but all of them is a huge mess.

0. Of course MCAS MUST NOT BE operative with AOA disagree. Minimal software mod.

1. one AOA clearly fails, why not use a switch to transfer everything to the other (manually or automatically). It's a 3 way switch (AOA input L/NORM/R). In the event of stick shaker on, AOA disagree, check if any AOA is stupid (75 is quite stupid), switch to the other side, no more alarms in the cabin, crisis over in 10s tops. minimal wiring loom mod.

Even if you don't do it:

2. We have now perfect data about the influence of AOA over airspeed. 30 knots tops over the full AOA range and airspeed. Probably 15 knots 0 to 15 degrees 0 to 300 knts, probably less than 5 knots in the really tricky areas (slow). Upon AOA disagree, both airspeeds should use a default AOA value (4 deg maybe) instead of throwing UAS. and offer a reading with a possible +-7 knot deviation. But keep autothrottle and autopilot, maybe a caution message (airspeed calculation inacurate, stay 20 knots away from limits). Not a really disturbing unreliable airspeed, just because of a few knots. Minimal software mod.

3. Same with altitude. (altitude calculation inaccurate, stay 1000 feet clear from limits). Minimal software mod.

So that the only remaining alarm would be a stick shaker plus AOA disagree, and you still have autopilots. Much, much easier to handle. But if this is still enough for you to have the aircraft out of trim and miss speed management,

4. If speed goes over 280, message: reduce speed to regain trim ability). Minimal software mod.

My point is: most probably ANY of those mods would have saved the day, and all of them are pretty evident.

To me the problem is simply a huge lack of effort at design level to 1) Imagine 2) prepare for failures.

Chances are that the very same secuence of events, without MCAS final strike, has happened more than once before in other 737 variants (AOA fails, unreliable air data, stick shaker, big confusion, lack of proper aviation and or navigation and possibly all the way to overspeed and uneffective trim). Only without MCAS the aircraft would have been more or less in trim and therefore not nosediving and making the news.

Completely agree, great post, I have been thinkig along the same lines since the first crash, this one only reinforces that.

0) I think Boeing is working on that belatedly.

1). I flew the F50, and you could silence all/most alarms with a dedicated switch on one panel. I have read several accident reports that made me wonder if the crew would have done better without distracting and conflicting (stick shaker and over-speed simultaneously on Aeroperu flight PL603) error messages. Having a switch to deselect a system that gives an erroneous indication is an established concept in certifying aircraft (, and I think it should be a mandatory re-fit to all B737). Having one stick shaker go of on the failed AOA side with no other way to switch it off than going through the CB-panel isn't good enough.

2) + 3) Seems sensible, there might be areas in the envelope where this wouldn't work, so I can't positively endorse without more info.

4) Yes, UAS/AOA failure, max speed should be kept lower, so advise the pilots to lower their speed by reducing power is good, however, just lowering the limit so the clacker goes of brings me back to item 1)


Definitely Boeing needs to:
-Limit MCAS authority, and preferably by adding aerodynamic fixes like tail strakes.
-Disable MCAS in the case of AOA disagree.
-Install the AOA indicator and AOA-disagree indicator, preferably better than the current way.
-Install an AOA left/norm/right switch that limits error messages/stall warnings for those cases where it is clear to the crew which one is wrong.
-Bring back the option to disable auto trim (AP, STS ,MCAS, LAM), without losing the thumb-trim.
-Improve the NNC, to differentiate between MCAS and "regular" runaway trim.
-Verify it is possible to trim the aircraft back to in-trim from a runaway trim, aircraft full AND situation at low altitude, and see if there is any speed restrictions required for this, for all B737.
Obviously al of this should be paid by Boeing.

Maybe not all are required, but at this point I think Boeing better go the extra mile to make sure this doesn't happen again.

Also I do believe there should be more required training for pilots and more push in the SOPs to manually handle the aircraft, so people will not try to switch on the AP to resolve a problem requiring manual flight.

[hec7or]

The inference that manual trim was not available may not be correct, in fact the report refers to "manual electric trim" meaning the control column trim switches, this is in fact the "main electric trim", as distinct from manual trim. It is possible that the FO misunderstood the Captain's request for manual trim and attempted to trim by using the control column trim switches which not surprisingly did not work due to the operation of the cut out.

I think it is possible that the FO may have tried to use the control column switches at the Captain's request rather than winding the trim wheel due to the stress of the moment, even though he had only just selected the cut out. The FO's statement at 05:41:54 that "it is not working" would appear to me that the control column trim switch was not working, whereas if the manual wheel was jammed I'm sure he would have said something along the lines of "I can't move it" or "it is jammed".

I base this on my experience on the NG, where I have heard pilots and instructors both in simulator training and normal operations referring to trimming "manually" meaning manual operation of the electric trim switches, I've never seen anyone actually manually rotating the manual trim wheel in the aircraft during flight.

[hans brinker]

Disagree. May address the issues that caused the latest accident, but contradicts the entire concept of the 737's instrumentation system, and will invalidate the safety calculations on which certification is based, as well as possibly opening the doors to other failure modes.

The 737 instrumentation is a dual-redundant system, comprising two completely separate systems such that in the event of a single failure one completely operational system is still available. With the aid of appropriate disagreement monitors, standby instruments and checklists, pilots are trained to detect and diagnose such failures and take appropriate action.

This system was state-of-the-art at the time the 737 was launched and is still in use in smaller, non-FBW airliners. It is totally adequate for its stated task, that is to provide information to a well-trained human crew. It should never have been allowed to provide inputs to a system that will automatically drive flight control surfaces.

Respectfully, I don't agree with you. The concept of the 737 has been changed dramatically from the original 93' span/94' length, 110K Lbs to the current 117' span/118' length, 195K Lbs. Adding STS, LAM, and now MCAS also contradicts the original B737 instrumentation system. The B737 overhead panel should have been thrown out when the designed the NG, and definitely with the MAX (FYI, DC9 and B717 are the same type rating). Having a switch to deselect a faulty indicator does not open the door to other failure modes. Not having an AOA disagree light as standard is just bad/cheap design (and Boeing agrees, all their MAXes will be retrofitted, and I believe all their more recent designs use 3 AOAs). Not informing crews about MCAS was the wrong thing to do, and not having a checklist for it letting crews re-trim the aircraft to neutral before using the cut-out for MCAS failure (as opposed to regular runaway trim) IMHO was a big mistake, just like certifying MCAS working on one AOA at a time was a big mistake.

[slacktide]

The peak is the FAA "Continued Airworthiness Notification to the International Community" dated March 12, a document type that was non existant before this date, is not based on ICAO rules and had just one obvious purpose. CMA.


CANIC was actually an outcome from the Comair 5191 crash. One of the NTSB findings related to poor inter-agency communication between various national and international certification authorities which delayed dissemination of training material that could have prevented the crash. This may be the first time that a CANIC was issued, however it is not a document type that was invented in the past few months.

"Recognizing the need for improved authority-to-authority communication, on September 26, 2006, the FAA released Order 8040.5 (https://lessonslearned.faa.gov/Comair3272/Order8040_5.pdf) describing the policy and procedures for developing Federal Aviation Administration (FAA) airworthiness directives (AD) on imported products where the State of Design Authority has issued mandatory continuing airworthiness information (MCAI). The order introduced a process for evaluating all MCAI and determining whether individual MCAI meet certain criteria that would permit a quicker issuance of an FAA AD.Further, the FAA has implemented a process for Continued Airworthiness Notification to the International Community (CANIC) that provides notification to other international regulatory authorities when the FAA issues an airworthiness directive. This is the reciprocal action to that identified above in FAA Order 8040.5. Further, the FAA has instituted a process of regular continued operational safety program reviews with all manufacturers who hold, or have applied for, FAA type certificates on their aircraft. This review program allows a more open and consistent avenue of communication between the FAA, counterpart regulatory authorities, and manufacturers, should airworthiness issues arise."


https://lessonslearned.faa.gov/ll_main.cfm?TabID=1&LLID=24&LLTypeID=10

[hans brinker]

Maybe in a 737, But it's wasn't in other jets, like the Fokkers. The trim wheel is just geared ..again question the 737 design..are so many clack clack clack turns necessary?

Late reply, but:
It is needed because of the force required to move the THS at high speed due to the hinge being at the back end. This causes the airflow to incraese the required trim force, had the THS been hinged at the front and and the jackscrew at the trailing edge of the THS the force required to trim would have decreased with an increase in speed. I am not a designer so I have no idea if you could even have built it that way, but I believe aerodynamically speaking this is the reason so many revolutions are required.

[bsieker]

Electric Trim Availability?

It's been pointed out that the range allowed for electric trim is less than can be obtained from the trim wheel (airload permitting).

Does that mean electric trim can not be used to return trim outside its range back to within its range?
No, the manual says explicitly that electric trim can always be used to bring it back into the normal range, but not to move it outside that range:

from 737NG FCOM 9.20.8 Stabilizer Trim:
In the event the stabilizer is trimmed to the end of the electrical trim limits, additional trim is available through the use of the manual trim wheels. If manual trim is used to position the stabilizer beyond the electrical trim limits, the stabilizer trim switches may be used to return the stabilizer to electrical trim limits.

Bernd

[hans brinker]

Obviously hitting the mechanical limit disables trimming. It's a hard limit. But there are also electric switches preventing you from reaching the full nose down (and up) position using electric trim even before you hit the mechanical limit. Boeing regards this additional limitation as a safety feature. And indeed, in case of electric trim runaway, it can limit the amount of trim the runaway could apply, so it can improve safety in some situations.

Later edit:

You can read in more detail about that in the latest Satcom Guru article: https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-range.html

In that article there is a table describing the available ranges for the various types of electric trim, compared to manual trim with the trim wheels.

For example, for the 737-800, the full trim range available with the trim wheels is -0.20 to 16.9 units. For manual electric trim with the flaps retracted the range available is 3.95 units to 14.9 units, so far away from the mechanical stops.

That's what the EASA document was talking about. You can't access the full range of mechanical trim positions using manual electric trim. With the flaps retracted on the 737-800 you would only have access to a range of 10.95 units of trim out of the total range of 17.1 trim units available with the trim wheels.

Unfortunately MCAS doesn't use the same limits as manual electric trim, so it can bring the trim closer to the full nose down limit. In the Ethiopian flight it manages to bring it to 0.4 units of trim at some point.

Question, when it says manual electric trim is unavailable outside of the range you mentioned, does that mean in both directions? I understand you can't use electric manual trim to go further ANU than 14.5 and not further than 3.95 AND, but if you find yourself with the flaps up and full AND trim can you use the thumb switch to correct, or do you have to crank the handle till reaching 3.95 AND trim beforhe the thumb switch works? (all this based on me thinking the low number being AND, and the high number ANU)

Asked and answered while I was typing:

At initial stick shaker, the aircraft can be expected to be in trim or not far from it. Better to head off MCAS at the pass than let it compound an already difficult situation to one where recovery is uncertain.

Electric Trim Availability?

It's been pointed out that the range allowed for electric trim is less than can be obtained from the trim wheel (airload permitting).

Does that mean electric trim can not be used to return trim outside its range back to within its range?

No, the manual says explicitly that electric trim can always be used to bring it back into the normal range, but not to move it outside that range:

from 737NG FCOM 9.20.8 Stabilizer TRIM:
Quote:
In the event the stabilizer is trimmed to the end of the electrical trim limits, additional trim is available through the use of the manual trim wheels. If manual trim is used to position the stabilizer beyond the electrical trim limits, the stabilizer trim switches may be used to return the stabilizer to electrical trim limits.

Bernd

[Smythe]

Main Electric trim:
Flaps retracted: 3.95 - 14.5 units
Flaps extended: 0.05 - 14.5 units
AP trim 0.05 - 14.5 units
Manual trim: -0.2 - 16.9 units

0 degrees is 4 ANU

Interesting the green band on the NG is 1.5 to 6.5, while on the MAX it is 2.5 to 8.5

I saw a report where thrust was at 94% to impact?

[deltafox44]

At initial stick shaker, the aircraft can be expected to be in trim or not far from it. Better to head off MCAS at the pass than let it compound an already difficult situation to one where recovery is uncertain.

Electric Trim Availability?

It's been pointed out that the range allowed for electric trim is less than can be obtained from the trim wheel (airload permitting).

Does that mean electric trim can not be used to return trim outside its range back to within its range?
Unbelievable ! But that would explain why the electric trim ANU stopped twice at about the same position (2.3/2.4 units).

[Bratchewurst]

QUOTE]Hans Brinker wrote:
Definitely Boeing needs to:
-Limit MCAS authority, and preferably by adding aerodynamic fixes like tail strakes.
-Disable MCAS in the case of AOA disagree.
-Install the AOA indicator and AOA-disagree indicator, preferably better than the current way.
-Install an AOA left/norm/right switch that limits error messages/stall warnings for those cases where it is clear to the crew which one is wrong.
-Bring back the option to disable auto trim (AP, STS ,MCAS, LAM), without losing the thumb-trim.
-Improve the NNC, to differentiate between MCAS and "regular" runaway trim.
-Verify it is possible to trim the aircraft back to in-trim from a runaway trim, aircraft full AND situation at low altitude, and see if there is any speed restrictions required for this, for all B737.
Obviously all of this should be paid by Boeing.[/QUOTE] What stands out most to me in reading this entire thread is that, while MCAS appears to have been activated in error on 4 occasions in some 500,00 total cycles of the MAX fleet, it appears to have activated correctly precisely zero times. This suggests to me

1) that the certification requirement that MCAS was intended to meet was excessive and not really required for safe operation of the aircraft; and

2) that, had MCAS been designed to deactivate itself upon AoA disagree and done nothing else (including notify the flight crew), neither these two accidents would have happened nor would have any other related to the certification requirement.

Based on the numbers to date, the statistical probability of an AoA disagree sufficient to deactivate a well-designed MCAS happening on the same flight on which the flight crew managed to get near to an accelerated stall is vanishingly small.

Regarding much of the MAX design being grandfathered under the certification process, it's worth noting that the NG series (which was also grandfathered) has essentially the same accident/fatality rate as the A320 series, which suggested that grandfathering the NG had no effect on operational safety.
​​​​​​​
Hans Brinker also wrote:

​​​​​​​1). I flew the F50, and you could silence all/most alarms with a dedicated switch on one panel. I have read several accident reports that made me wonder if the crew would have done better without distracting and conflicting (stick shaker and over-speed simultaneously on Aeroperu flight PL603) error messages. Having a switch to deselect a system that gives an erroneous indication is an established concept in certifying aircraft (, and I think it should be a mandatory re-fit to all B737). Having one stick shaker go of on the failed AOA side with no other way to switch it off than going through the CB-panel isn't good enough.

Perhaps the user interface aspect of a cockpit where multiple alarms are going on and off deserves more attention than it has received to date. In particular, the issue of the stick shaker creating such a racket seems to be a real issue. It's far easier to be overwhelmed by aural cues than by visual ones.

[hans brinker]

Unbelievable ! But that would explain why the electric trim ANU stopped twice at about the same position (2.3/2.4 units).

Apparently always possible to electric trim back to middle even when outside of normal electric manual trim range.

No, the manual says explicitly that electric trim can always be used to bring it back into the normal range, but not to move it outside that range:

from 737NG FCOM 9.20.8 Stabilizer Trim:
In the event the stabilizer is trimmed to the end of the electrical trim limits, additional trim is available through the use of the manual trim wheels. If manual trim is used to position the stabilizer beyond the electrical trim limits, the stabilizer trim switches may be used to return the stabilizer to electrical trim limits.

Bernd

[Airbubba]

The inference that manual trim was not available may not be correct, in fact the report refers to "manual electric trim" meaning the control column trim switches, this is in fact the "main electric trim", as distinct from manual trim.

I got the same impression reading the preliminary report.

From the report, emphasis mine:

Between liftoff and 1000 ft above ground level (AGL), the pitch trim position moved between 4.9 and 5.9 units in response to manual electric trim inputs. At 1000 ft AGL, the pitch trim position was at 5.6 units.

I'd like to know exactly what terms were used in this exchange:

At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working.

I still can't figure out why nobody pulled back the power with continuous overspeed warnings on both sides and obviously too much thrust for attempted level flight.

[PJ2]

Do you know how many hand inputs from the pilot will take to complete one turn? Three, four? Supposing the answer is three, the pilot will have to make 44 hand movements to change one degree. If the pilot is able to execute one turn in 4 seconds (fast), a change of only one degree will take 59 seconds, or one degree per minute.
Not enough time to recover from a dive. If my math is correct, the only way to counteract MCAS input is with electric trim. But if you need to cut off trim motors to "kill" MCAS, how the pilot will manually turn the trim wheel to achieve enough amplitude to cancel MCAS inputs?

The key, as stated by Ranrair, (which see above) is to react immediately, before the trim gets beyond the point where the only functioning control is the mechanical trim wheel & cable drum.

The problem is, as has been stated by many now, MCAS actions mask what is essentially a runway-by-increments stabilizer, and there was no training or FCOM information for pilots to assess the behaviour of the system for themselves and when faced with heavier control column and UAS + #1 stall warning right after liftoff, tried to diagnose the problem without the necessary tools and experience to do so, costing valuable response time.

[Smythe]

Simulation of airflow around B737 body

https://www.youtube.com/watch?v=-K3KwdCwsTk

[positiverate20]

I still can't figure out why nobody pulled back the power with continuous overspeed warnings on both sides and obviously too much thrust for attempted level flight.

Any reduction in power would have created a significant AND moment. The longitudinal acceleration was positive throughout- right up until the final MCAS AND. (0.1g at end equivilant to 0-60mph/0-100kmh in 27seconds.) The actual acceleration provided by thrust would need to be calculated using both vertical (above 1g) and longitudinal (above 0g) acceleration data.

That thrust moment of the engines coupled with the aerodynamics of the engine cowling was in fact assisting them with pitch (and would do so with diminishing effect up until VH) The fact that it also masked the true trim when they initially cut it out is possibly the reason why they didn't attempt manual trim wheel as soon as cut outs were flicked.

[DaveReidUK]

Unbelievable ! But that would explain why the electric trim ANU stopped twice at about the same position (2.3/2.4 units).

Electric trim limit on the NG (may vary slightly by series) is apparently 12.5 units ANU, can't think the Max will be much different.

[Vilters]

I still can't figure out why nobody pulled back the power with continuous overspeed warnings on both sides and obviously too much thrust for attempted level flight.

Crew/ Confusion/ Overload

When multiple warnings go off at the same time with conflicting informations the crew gets in trouble.

Stick shaker = STALL warning, and at low altitude that is something to be scared off so you try to get the nose DOWN and power UP. And at the same time one gets HIGH speed indications.

Priority ONE, if the crew get the time to troubleshoot before crashing, is to figure out what warnings are true and what warnings are false.

Then add that the LEFT AOA and the RIGHT AOA give different info, add an anti STALL system, (MCAS) that starts playing with your feet and trim position, and crew overload exceeds available time to find out what is true and false.

Add the human factor too. Every beginning pilots get : Lesson 1, first minutes => Speed is life.

Each and every pilot, from beginning PPL upwards is more scared of a low altitude stall then off an overspeed. => Safety first => So the Power stays UP.

[MemberBerry]

Unbelievable ! But that would explain why the electric trim ANU stopped twice at about the same position (2.3/2.4 units).

I think actually it may be related to this:

Interesting the green band on the NG is 1.5 to 6.5, while on the MAX it is 2.5 to 8.5

Maybe they only applied as much electric trim as needed to bring it close to the green band, that starts at 2.5 on the MAX. The stick shaker suggesting they are close to a stall might have made them reluctant to use more.

I don't think there was anything preventing them to apply more nose up trim if they wanted to, until they used the cutout switches.

[hans brinker]

Any reduction in power would have created a significant AND moment. The longitudinal acceleration was positive throughout- right up until the final MCAS AND. (0.1g at end equivilant to 0-60mph/0-100kmh in 27seconds.) The actual acceleration provided by thrust would need to be calculated using both vertical (above 1g) and longitudinal (above 0g) acceleration data.

That thrust moment of the engines coupled with the aerodynamics of the engine cowling was in fact assisting them with pitch (and would do so up until VH) The fact that it also masked the true trim when they initially cut it out is possibly the reason why they didn't attempt manual trim wheel as soon as cut outs were flicked.

Can any B737 pilot tell me how significant the AND is from reducing the thrust from T/O power (in this case I believe it was at 94% N1), to a power setting giving 210kts F5 and 250 kts Fup at 10.000' ?
I fly brand A, so I have no idea, but an answer in units or seconds of thumb trim input would be helpful. The cowling wasn't helping, as I am sure most of the cowling was below the CG at the AOA they were flying,( it only provides an ANU moment at very high AOA)

Also, I have a hard time believing they left the power at full on purpose, as I read they set a lower altitude and speed in the window, presumably expecting the AT to reduce power.

[Banana Joe]

I give it a burst of trim every 10 knots during accelerating. I also have to counter STS trimming initially nose-up to maintain speed.

[BluSdUp]

Working for the B Team lately
Never was a Nr Man as in memorizing a heap of Pitch Pwr.
But I love Whatever It takes , then BallPark !
Let me give it guess:
94 N1 to say 70% N1 ca 240kts F5, ehhh. 1 to 2 units ANU say 1.5 ( Trim CHANGE)
Pure guess

[pchapman]

Not sure about jumping into this 3300+ post thread but here goes:
I'm concerned about the crew's actions both for the manual trim attempt, and with the electrical trim attempts just before they lose control. And I can't help but distrust the inexperienced First Officer more.

To summarize:
- they had the MCAS pitch control problems
- got the Cut-out switches to stop MCAS from trimming down any more
- they're flying OK, got some altitude banked, although still in crisis mode, still having to hold back pressure, deal with the one stick shaker, overspeed clackers after some point, and what not
- there's a discussion about the manual trim not working. We don't know the exact words used.
- Interpretation: Might have to do with high forces on the manual trim wheel, but it is also unclear whether the First Officer really doing what was expected. Was he just hitting the thumb trim switch, or trying to roll the trim wheel (without much experiences of the forces that might be involved) or did he actually have the fold-out handle open and still find he was unable to turn it?
- either way, they keep flying OK for another minute or so
- then there are the 2 very short electrical up trim attempts (as others have also commented on). I agree that the graphs show a small up trim effect. Hard to see on the graph but really does look like a little bit of nose up trim change. Barring any totally unexpected electrical issue, this is only possible with electric trim turned back on!
- very soon after, MCAS kicks in, trimming a bunch nose low, and the pilots lose control and nose over.

The preliminary report gives no indication that the pilots discussed turning electric trim back on. Nothing about, "Despite the AD saying to leave it off, you turn electric trim back on, I'll trim out these awful control forces, you turn it back off before this thing tries to pitch down again."
Did the Captain try turning it back on? Or was the First Officer fiddling around on his own? Trim gets turned back on with no consultation and but only 2 ineffective short trim activations are made. Were jackscrew forces so high that electric trim wasn't working well? Who knows, I'll leave that to the experts. But the electric trim attempts were two short blips, not like trying mashing that button down a full 5 seconds to see if they got some effect out of it.

That really messed them up, ineffective trim attempts without killing the electric trim system again afterwards.

[edmundronald]

Let me see:
1- All the update training for a pilot to fly a Max is 1 hour on an iPad, says the FAA, and Boeing.
2- A couple of max crashed.
3 - Older 737s seem safe in the hands of the same pilots.

The FAA and Boeing agree point 1 was not right.
Now the FAA and Boeing tell us that a fix will make point 1 right.
Should we believe them?

[gums]

Salute!

Getting into some good "what if" and "there I was" stuff, and some of it should be of interest to the Boeing folks in the design shop as well as some FAA folks. As Mawtha would say, "it's a good thing".

- I am willing to buiy most here a beer if the design folks and fault tree analysis folks ever considered activation of MCAS at 400 ot 500 ft ( depends on your procedures for flaps and such, but remember that in most of my jets I just raised gear when having a positive rate of climb, and then flaps a few seconds later; Viper was together, as flaperons went up and down with the gear handle)

The doggone thing (MCAS) seemed to be geared to a medium or high altitude turning maneuver at "holding" airspeed/AoA. Can't help but feel they never envisioned it cranking in over 2 degrees of trim at low altitude and low mach with stall warning going and stick shaking and warning lights illuninated.

- Why change the trim cutout switch wiring? You know. One for HAL and the other for me seemed to be the standard from day one. That configuration would please many of the Chuck Yeager folks on this forum, and I agree with them. At least I know what I have to play/work with. That aspect of the flght controls is not a consideration in the later model Airbus, Raptor or Stubby ( F-35) flight controls because you need electric power to the actuators 100% of the time! Duuuhhhh? We had a serious power supply design defect in the early Vipers, and it took two or three crashes to figure it out. After that, walla! And for you millenium yutes, our early FLCS computers were analog chips, not digital. They were very robust when volts and amps went into la la land because they failed gracefully. Later digital FLCS boxes had a more robust power supply configuration, because when those puppies go west. it is all or nothing!
In all fairness, in my leading edge flap failure adventure I used the only flight control switch besides for the deep stall direct mode doofer - the flap switch. It allowed me to lock the opposing flap to keep a more predictable (?) configuration, LOL.

- As with most pilots here, I feel badly the crew did not pull the power back as the 610 crew did. With all that was going on, I cut them a little slack. There are two good lessons to be learned, though. 1) Aero forces on the stab can give you a major headache if you are going fast with a trim problem, and 2) you should try to follow the same takeoff-to-climb sequence you did a thousand times. Remember to pull back power to climb or low altitude maneuvering power and pitch.

There many other lessons and design considerations to be had with these two crashes. I just hope the 737 pilots here are reading our whines and theories and war stories, then fold some scenarios into their personal procedures.

Gums sends...

[OldnGrounded]

I continue to find it disturbing and surprising that more than a few posts are focused on blaming, or at least strongly suspecting, crew error as a primary cause of the Ethiopian crash.

Surely, it should be clear, from all we have learned and discussed in the weeks since that accident, that the crew was faced with a situation that almost any crew would have found very difficult, if not impossible, to deal with successfully. If mistakes were made, they were made in an environment where not making mistakes was extremely unlikely and in which they would never have found themselves if the OEM and the regulatory authority had not made fundamental and extraordinary mistakes in designing and certifying the aircraft. And those entities weren't facing imminent sudden death when they screwed up.

[Ian W]

Any reduction in power would have created a significant AND moment. The longitudinal acceleration was positive throughout- right up until the final MCAS AND. (0.1g at end equivilant to 0-60mph/0-100kmh in 27seconds.) The actual acceleration provided by thrust would need to be calculated using both vertical (above 1g) and longitudinal (above 0g) acceleration data.

That thrust moment of the engines coupled with the aerodynamics of the engine cowling was in fact assisting them with pitch (and would do so with diminishing effect up until VH) The fact that it also masked the true trim when they initially cut it out is possibly the reason why they didn't attempt manual trim wheel as soon as cut outs were flicked.

At the speed they were traveling there should be no significant nose down pitch from reducing the power to a reasonable level.
The engine cowling lift is only significant at high AOA (that's why MCAS only operates when it thinks the aircraft is at high AOA). The aircraft was actually flying with a low AOA. A reduced speed would have increased the elevator authority and reduced the load on the manual trim.

[nevillestyke]

so advise the pilots to lower their speed by reducing power is good

But reducing power pitches nose down, due to the aerodynamics of the aircraft. How much would airspeed reduce? Parking brake is of little use.

[positiverate20]

At the speed they were traveling there should be no significant nose down pitch from reducing the power to a reasonable level.
The engine cowling lift is only significant at high AOA (that's why MCAS only operates when it thinks the aircraft is at high AOA). The aircraft was actually flying with a low AOA. A reduced speed would have increased the elevator authority and reduced the load on the manual trim.


A reduced speed by having a lower thrust setting to begin with, yes more controllable.

Reducing thrust from a higher thrust setting incurs a nose down moment. Basic stuff.

We're possibly getting confused between velocity and acceleration? Momentum around the CG?

If thrust were to be reduced for this flight it would have been best to do immediately after TO. But, in this case, immediately after takeoff was stick-shaker and airspeed warning- not the optimum time to reduce thrust when hundreds of feet AGL.

[astonmartin]

I'm still struggling with the though that a grossly mis-trimmed stab on an NG cannot be recovered by either electric trim or by the strength of 1 or even 2 pilots cranking the wheels when the aircraft is at certain parts of the flight envelope.

As covered by others above, it seems bizarre to rely on having the airspace and time available to perform an acceleration or deceleration to a trimmable speed and/or perform a manoeuvre in the opposite sense to what you are trying to achieve in order to put the stab in a safe position.

Hopefully Boeing can enlighten us as to which parts of the performance envelop allow for PF solo cranking, PM dedicated cranking, both pilots cranking or just plain impossible to crank the wheel due to aerodynamic load. The NG is still flying and I am sure the AOCs would like to know, even if the FAA is asleep at the wheel at a benign 1G.

During testflights with the B737 PG and NG I have used the stabilizer trim wheel many times. Also with high speeds, it is possible to crank the wheel. But with more elevator input (ANU), it becomes increasingly difficult to trim the stabilizer (ANU). This is because the (ANU) elevators push down on the trailing edge of the stabilizer.

Furthermore, the phenomenon of ‘elevator blowback’ may have played a role at the last, high speed phase of the flight. If that was the case, the elevators were blown back towards neutral, despite the combined hydraulic and muscle forces.

[ManaAdaSystem]

Let me give it guess:
94 N1 to say 70% N1 ca 240kts F5, ehhh. 1 to 2 units ANU say 1.5.
Pure guess

68 tons of -800 at 10000 ft with FL5 and 240 kts will need about 72-73% N1, but the trim will stay around 4 units.
I don't think you'll ever see the trim near full AND during normal ops.

[BluSdUp]

I do appreciate the sensory overload that ensued after AP dropped out on Flap retraction.
This is why I am a strong believer in 3 things in an Emergency with control problems!
1 Fly the Aircraft ( Analyse)
2 Fly the Aircraft ( Doing nothing makes it worse? No, good!)
3 Fly the Aircraft ( Memory items IF it does not make it worse)

A terrible situation for this crew.
No blame
I just want to learn, and most important : Boeing has to learn or else,,,,,,,,
Respectfully
Cpt B

[Bleve]

I don’t fly the 737 Max, but after doing a bit of ‘what-if-ing’, I’ve come to the conclusion that if I were a Max pilot and had stick shaker on take-off, I would not fully retract the flaps. I would retract to Flaps 1. My experience on other Boeing’s (767 & 744) is that Flaps 1 provides the best manoeuvre margin to the stall and in the 737 Max would prevent MCAS doing it’s (evil) thing.

[SteinarN]

Slightly off-topic.
Boeing is slowing production of 737 by one fifth, from 52 to 42 a month, effective in about ten days.

Boeing will slow 737 production by one-fifth; no layoffs planned (https://www.seattletimes.com/business/boeing-aerospace/boeing-will-lower-737-production-rate-but-says-no-layoffs/)

[Reluctant Bus Driver]

I don’t fly the 737 Max, but after doing a bit of ‘what-if-ing’, I’ve come to the conclusion that if I were a Max pilot and had stick shaker on take-off, I would not fully retract the flaps. I would retract to Flaps 1. My experience on other Boeing’s (767 & 744) is that Flaps 1 provides the best manoeuvre margin to the stall and in the 737 Max would prevent MCAS doing it’s (evil) thing.

Thats pretty poignant in this situation because MCAS does not fire with the flaps out, or so I have been told. It's highly doubtful they would have known or thought of that. A really bad situation..

[Cat Techie]

Any electronic system on any aircraft should have a means of isolating the power to that system. Even if it is critical. Is the MCAS system so infailable that such a system does not have a CB tied into it to isolate it? I am not rated on 73s but know the basic stall identification and warning systems on other types. One they do not operate until the weight offs + time delay occur and there is simple methods to deactivate.. I smell a massive regulatory and manufacturer fail that should have been apparent with the Lion Air crash. Then again I am a techie, not a system designer.

[BluSdUp]

No no no
Me and my short sentences . It was a response to the Trim demand on pwr change in a previous post!
So spot on then , 94% TOGA at 5,6 trim
Then 73%
Trim I might have got wrong as it is not in my scan, but initially we trim AND after lift off and if You are right with 4 units we do not need a big ANU trim , once pwr is established, speed 210 to 240.
Having again read Hans B question , it is twofold
210 kts F5 hardly any change after INITIAL trim at say V2+ 20!
240 F-UP is a good 1 unit plus
Yeah , so lets say 4 to 5 units.
In short , SMALL changes for a safe speed with regards to stall and manual wheel trim, me thinks!
Idle on the other hand out of trim after 101% proved to be more of a problem for FlyDubay

[fotoguzzi]

Maybe they only applied as much electric trim as needed to bring it close to the green band, that starts at 2.5 on the MAX. The stick shaker suggesting they are close to a stall might have made them reluctant to use more.

[Not a pilot] Yet they had the control column way back (after the ground proximity warning) and, at times, called out, Pull together, and, Pitch together. They decided pitch was not enough.

I think it's still unclear whether they were both on the same page about elevator pitch, manual/electric pitch trim, and hand wheel pitch trim, but do stall concerns fit in with the above?

They spent a total of fifteen seconds working on pitch trim; first the FO, later, "together." It's not clear to me whether at any point they each freed up a hand to use on the hand wheels.

[F-16GUY]

Gums,

Like you I have absolutely zero experience in modern liners like the MAX or NEO. But when reading accident and incident reports, I get the feeling that beside the lack of proper and sufficient training, the modern liners are needlessly over complex, not user friendly, have poor and unintuitive man-machine interphase and when their systems degrade, they degrade very ungracefully. I know both Airbus and Boeing pilots who all tell me their machines are a joy to fly when all bells and whistles are working properly, but I don’t understand why the manufactures have chosen to go down the path of complexity, when I know from personal experience that an aircraft can be built in another way.

I know that most normal pilots are in love with their specific aircraft type, but going through the types I have flown in my career so far, the F-16 stands out above all other types in the way it is designed. For some reason it appears that when the F-16 was designed, Boyd, Hillaker and the rest of the so-called Fighter Mafia members actually understood what the pilots needed both when every system was working, but also when things went bad. They managed to build a very simple, user-friendly and from a technical point of view genius aircraft.

To begin with, the flight control system, the worlds first full FBW system in a combat aircraft, was very effective, robust, simple, reliable (when the first hiccups were dealt with) and best of all, so fantastically pilot friendly, that most pilots will feel that the aircraft becomes an extension of their body after half the take-off run on their first flight in the aircraft.

I don’t understand why it is not possible to build an airliner with such a clever flight control system? As you described, who needs dedicated flap levers? You only need flaps during take-off and landings, so why not integrate the flap function with the gear handle, as you need your gear to be down when taking off or landing. Flaps that can be manually selected down without the landing gear if a situation ever arises where it is needed (intercepting a cessna at 90 knots), and flaps that will retract by themself if an overspeed is about to happen. And by the way, the system changes the control gains from take-off/landing gains to cruise gains with the gear handle position. Automatic leading edge flaps that drop down on rotation to increase lift, and instantly go up to dump lift when touching down on landing. No need to arm them like spoilers and no need to stow them in case of rejected landing. A wing that changes shape (again by the use of leading edge flaps), so as to always have the optimal shape for the actual flight regime (with an envelope much wider than the typical airliner).

And in the very rare case where the system malfunctions, it degrades so gracefully that the pilot probably wont even notice any change in flying characteristics (like when the bus changes to direct law). Loose a control surface (loose like in it has fallen off), have a runaway elevator trim go full nose down, or even worse, have a LEF pointing straight up like in gums LEF incident, and still be able to counteract the roll, pitch or yaw with less then superhuman power, by just applying a bit more force then normal on the side stick.

And all this was designed in the mid 70’s. One would think that it would be possible to make an even better flight control system today. A system that would help the pilots instead of defeating them. Of course, complex systems are fine and work well if the operators are well trained, experienced pilots that understand the systems and all of their sub modes, but the average pilot today as I see him/her, is only trained to the minimum requirements, doesn’t get a lot of stick time, and doesn’t really understand the system 100%.

Aircraft engineers, is it not possible to keep it simple stupid anymore?

[Derfred]

I don’t fly the 737 Max, but after doing a bit of ‘what-if-ing’, I’ve come to the conclusion that if I were a Max pilot and had stick shaker on take-off, I would not fully retract the flaps. I would retract to Flaps 1. My experience on other Boeing’s (767 & 744) is that Flaps 1 provides the best manoeuvre margin to the stall and in the 737 Max would prevent MCAS doing it’s (evil) thing.

That's what I learned from LionAir, except that I would have left the flaps at 5 and adopted a pitch attitude of 10 degrees, confirmed that the stick shaker was false, checked for IAS disagree, and set 80% N1 (terrain permitting), flight directors and autothrottle off. Climb above a safe altitude and then carefully run the Airspeed Unreliable checklist, which would identify correct speed on the RHS. Engage autopilot B as per the checklist and return to land. Don't retract flaps. MCAS won't activate and stab trim cutout switches can remain in normal.

Now, I concluded that from the comfort of my armchair AFTER the Lion Air accident, so that if it happened to me, I would know what to do.

The Ethiopian crew obviously didn't, but neither did Boeing.

Mind you, I AM adopting a Boeing procedure here (the Airspeed Unreliable checklist) - It's just that I'm being choosey about which Boeing procedure to adopt and how, and using some additional system knowledge which we didn't have prior to the Lion Air report (i.e. flaps stops MCAS!).

[astonmartin]

I think engineers have more freedom when designing fighters, then when designing airliners.
It’s all about liability.

[GordonR_Cape]

I think engineers have more freedom when designing fighters, then when designing airliners.
It’s all about liability.

I think piggybacking onto a 50 year old airframe may be more of an obstacle, than any legal liability is, when designing flight controls.

[BluSdUp]

I trained 50 or 60 active Dutch F16 chaps in AMS on MCC Courses.
5 sessions in FFS A320 and later in B737-800
An absolute delight, BUT as they all remarked on the last night at the mandatory WetBrief.
" Dude, we respect You civilians a bit more now"
The thing is that the A320 was easy for them, when they realized , NO 4 handed , lightning quick selections!!
The Boeing 737 they wondered about?
"Which Museum did You steal this rig from"

In short:
Civil aviation has gone backwards since say mid 1990s.
I suspect the latest events will do to Aircraft Design and Certification what 9/11 did to Airport Security.
Without any direct comparison intended from me, of-course.
Regards
Cpt B

PS There is 9 flap settings on the 737.
I rest my case.
DS

[amc890]

F-16Guy I think you really know the an$wer.

[BluSdUp]

Yepp
Ibiza for 15£
Sorry 9£

[pilot9250]

So what happens next time somebody has a different type of problem for which they have had no specific training?

Depends on what the problem is.

If the problem is ill thought-out automation, incomplete documentation and missing training, then the answer will be fix the automation, revise the documentation and add training.

Which is what Boeing are doing here.

[yanrair]

The isolation for MCAS is the STAB OFF switches beside pilots knee. Anything that moves the stab goes through these switches. But, you would have to recognize the problem. Clearly the pilots knew nothing about MCAS like the rest of us. All they may have seen is the STAB running AND - nose down.

[EDLB]

It might be worth looking into an older crash A6-FDN. FDB 981. Strange that a 5000h PF sets 12 seconds of continuos stab down trim from which he could not recover. Was not a MAX.

[deltafox44]

I still can't figure out why nobody pulled back the power with continuous overspeed warnings on both sides and obviously too much thrust for attempted level flight.
Attempted level was FL320 !

With stall warning and attempting to clear the terrain, more speed means more potential energy, so I think overspeed was not on top of their priorities.

If Boeing NNC for trim runaway had included "reduce speed if manual trimming is too hard", perhaps they would have done it...

[OldnGrounded]

The isolation for MCAS is the STAB OFF switches beside pilots knee.

That's not isolation, it disables all electric trim. Isolation would mean disabling MCAS only.

[LowObservable]

Woof woof, it's dark here....

So the dog that hasn't barked, as far as I know, is this:

Aside from the three-crew Lion Air flight that preceded the mishap flight, where are all the crews who might have experienced an AoA failure that triggered MCAS at flaps-up, and handled the situation safely?

For this to happen means that one of the AoA sensors has to be bad from the start, that it has to be bad enough to call a spurious stall warning, and it has to be the sensor that is driving MCAS on this flight (the last being a 50:50 chance). How often has this happened in the MAX's history? I have not seen a single such account in this long thread (I stand corrected if I missed one).

Clearly, that number would provide some valuable context to the two occurrences when the result has been fatal.

[deltafox44]

But reducing power pitches nose down, due to the aerodynamics of the aircraft. How much would airspeed reduce? Parking brake is of little use.
The nose up moment of the engines thrust may be important at lower speeds, but negligible at higher speeds, since the thrust is constant but any other aerodynamic moments vary as the square of speed.

What about the pitch of airbrakes ?

[AndyJS]

Does anyone else think that maybe the very fact that they're trying to solve this through a software update may be part of the problem?

[OldnGrounded]

Does anyone else think that maybe the very fact that they're trying to solve this through a software update may be part of the problem?

I'm pretty sure that, as we learn more and more about the underlying issues, more people think just that, every day. I think a lot of us who have been following this closely will be surprised if the MAX gets back in the air quickly, with only a new software patch.

[airman1900]

MAX Saga Spotlights Flight-Deck Human Factors

MAX Saga Spotlights Flight-Deck Human Factors

Sean Broderick, Bill Carey and Ben Goldstein Washington

Details emerging from investigations into two fatal Boeing 737-8 MAX accidents in five months are fueling a heated debate over whether the pilots involved were adequately prepared to face their inflight emergencies or simply could not overcome failure modes rooted in a flawed design. Either scenario implicates flight-deck human-factors shortcomings that will reverberate far beyond the software upgrades Boeing is counting on to help get the 737 MAX fleet flying again.

While the investigations into the Oct. 29, 2018, crash of Lion Air Flight 610 (JT610) and the March 10 Ethiopian Airlines Flight 302 (ET302) accident are ongoing, links between the two have been established. In each case, the flight crews battled to keep a new 737-8 aloft while the aircraft’s Maneuvering Characteristics Augmentation System (MCAS) pushed the nose down by applying stabilizer trim. The MCAS, which was added to the 737 speed trim system to help the new model handle like its 737NG predecessor in certain flight profiles, relies on data from one of the MAX’s two angle-of-attack (AOA) vanes. In each accident, investigators have confirmed the aircraft was getting unreliable data from an AOA vane, which triggered repeated MCAS nose-down inputs.

Boeing is developing a software upgrade that will prevent the updated system from activating if it is fed erroneous data (see page 24). It also gives pilots ultimate elevator authority by limiting the degree of automatic nose-down stabilizer. Additional training and updated flight manuals will also be provided. These changes will be part of safety regulators’ demands to lift 737 MAX revenue-service operations bans that have grounded the 376-aircraft fleet since March 13.

The changes are a de facto admission that the MCAS needed improvement. Beyond that, questions about how well-prepared pilots were to deal with the system’s failure remain paramount in many circles. Boeing did not include any MCAS information in 737 MAX flight manuals, which some point to as an egregious oversight. It was only after JT610 that Boeing provided pilots with extensive details about handling the MCAS.

Many pilots say that though they do not agree with Boeing’s philosophy of keeping the system in the background, they acknowledge Boeing’s logic that an MCAS failure would be recognized as uncommanded stabilizer input and managed via the common “stabilizer runaway” checklist was reasonable. The checklist, which is the same on the 737NG and MAX and includes a step that cuts power to the stabilizer, is supposed to be common knowledge for airline pilots.

“Pilots of large aircraft are trained from Day 1. When the pitch of the aircraft is doing something you’re not telling it to do, you do a runaway pitch trim checklist,” Acting FAA Administrator Dan Elwell, a former airline pilot, told a U.S. Senate subcommittee during a March 27 hearing about the MAX. “In every plane I’ve ever flown, it’s called a memory item. You’re not fumbling through books. It’s a time-critical procedure, and you go to that.”

The European Aviation Safety Agency Executive Director Patrick Ky, speaking to European Parliament members on March 19, said the procedure “is not that complicated.” But the fact that it was not followed by the Lion Air crew suggests they were confused. “If they knew what was really happening, they would not have done what they did, and they would not have crashed,” Ky said.

The ET302 crew had the benefit of knowing about the MCAS, and investigators determined that they followed the prescribed procedure—at least in part. The MCAS activated and pushed the aircraft’s nose down. The crew responded with manual inputs via column-mounted trim switches, which countered only a portion of the MCAS nose-down input. The automated system, still receiving erroneous data, activated two more times, dropping the nose even more. After the third MCAS nose-down input, the crew toggled the cutout switches. Struggling to maintain altitude, they turned the system back on, which triggered the MCAS again.

Investigators are looking closely at how the ET302 crew reacted, and why they reactivated a system that they identified as central to their problem. One possibility: With power to the stabilizer cut off, they would have needed to move it by cranking a center-console-mounted wheel attached to cables and pulleys. This may have taken more time than they believed they had, or been too difficult, so they opted to reengage stabilizer power and try the column-mounted switches.

Another possibility: They may not have fully understood what they were facing. Boeing’s approach of keeping the MCAS in the background means its activation did not result in any cockpit warnings. Boeing’s assumption: Unwanted nose-down inputs, signified in part by a spinning trim wheel, would alert pilots to a runaway stabilizer and prompt them to execute the checklist.

“If I had been flying a MAX with stickshaker activation at liftoff after the Lion Air accident, shutting off the trim would have been accomplished in a matter of seconds, not minutes,” says one U.S.-based MAX pilot. “I probably would have activated the stabilizer trim cutout switches before the gear was even up. Why that didn’t happen on the Ethiopian flight is a mystery to me.”

The stickshaker warning, or artificial vibrating of the control column that signifies a stall is imminent, activated on both JT610 and ET302 because of the faulty AOA data. Meant to alert pilots of a problem, it can be more of a distraction than a help in certain scenarios,the MAX pilot says.

“Not only would the noise mask the operation of the trim [wheel], it is such a significant warning that it would command a lot of attention,” the pilot says. “Ultimately, it is not telling you anything useful, but it makes recognizing the trim runaway more difficult,especially since the trim was not continually running.”

The two MAX accidents underscore a larger concern: Is automation is beginning to supplant, instead of augment, basic flying skills? While airlines have long used it safely, pilots who typically fly with automation who were involved in accidents “made errors when confronted with an unexpected event or [when] transitioning to manual flying,” the Transportation Department Inspector General’s office found in a 2016 report to Congress.

“As a result, reliance on automation is a growing concern among industry experts, who have questioned whether pilots receive enough training and experience to maintain manual flying proficiency,” Transportation Department Inspector General Calvin Scovel said in the March 27 hearing. The initial results from the ET302 accident “raise concerns about pilots’ abilities to recognize and react to unexpected events,” he added.

The FAA now requires that Part 121 pilots be trained in specific abnormal flight conditions, including stall and upset recovery and loss of reliable airspeed, and that training on the responses be performed in full-flight simulators. But the recent 737-8 accidents have raised questions about the availability and capabilities of simulators, Scovel says. According to the FAA, “existing simulators do not fully replicate the 737 MAX aircraft, and no U.S. airline currently has a MAX simulator,” he says.

Most airline standard operating procedures “recommend and encourage” using full automation to control an aircraft for safety and efficiency reasons, observes Hassan Shahidi, Flight Safety Foundation (FSF) president and CEO. Automated systems can improve pilots’ management of the flightpath, particularly during reduced weather minima, relieving them from repetitive tasks. But by depending on automation, they revert to monitoring the system rather than actively flying the aircraft. There are various theories about how complacency affects pilot performance, says Shahidi, a former Mitre Corp. senior executive who started at FSF in January.

With all of the advantages it confers, automation is not a substitute for the function of the pilot, who ultimately is responsible for flying the aircraft, says Shahidi. With respect to pilot training, “there needs to be sufficient understanding for the basis of the automation—why there is automation in the first place—and what happens with partial or full-use” of a system, he says. Also, pilots should understand the importance of monitoring an expected function so they can take timely and corrective action if there is a malfunction.

Training that focuses pilots on abnormal situations is important, whether in a simulator or non-simulator environment, Shahidi advises. For example, pilots who fly with the autothrottle engaged, even in small aircraft, may lose the habit of regularly scanning the speed indicator. When the autothrottle disengages for some reason, the pilot may not readily notice or react to even large speed
deviations.

“Automation has the potential to cause significant issues if it is misunderstood,” says Shahidi. “Poor automation can reduce the pilots’ situational awareness and create significant workload as they are trying to figure out what the automation is doing, especially if the system fails. This certainly can lead to an aircraft getting into an undesirable state from which it is difficult or sometimes impossible to recover.”

The FSF issued a position paper on pilot training and competency in March 2018 saying the commercial aviation industry has reached a “crossroads” in determining how pilots should be trained and mentored and questioning whether the current approach can produce a “sustainable quantity and quality of pilots” for the expected future demand. Boeing has forecast a need for 790,000 new civil aviation pilots over the next 20 years. The Asia-Pacific region leads demand with a requirement for 261,000 new pilots over that time, the manufacturer predicts.

Shahidi concurs when asked if there is a need for more standardized pilot training across airlines that have different standard operating procedures and training requirements beyond what is minimally required by aviation authorities and manufacturers.

“Moving forward, especially in light of the fact that we’re looking at significant demand for new pilots in many of these regions, it is important to harmonize the level of training that is required,” he says.

Among the recommendations the FSF white paper calls for are “competency- or evidence-based” training programs that are not solely hours-based and for maximized use of simulation devices. Pilot performance criteria should be universally recognized, and the International Civil Aviation Organization tapped to define guidelines for the performance required of flight academies.

Shahidi points to the role of what he calls nontechnical competencies of communications, analysis, problem-solving, decision-making and leadership in piloting an aircraft. “It is not just understanding [which buttons to push] or disengage, but—as part of a holistic approach to training—these basic skills are important,” he says.

Fundamentally, mastering these skills is both more realistic and more valuable than practicing scores of failure-scenario combinations.

“We are not trained in many potential emergency situations,” says the U.S.-based MAX pilot. “But we are trained to fly the airplane, prioritize, work together and diagnose whatever problem is facing us. In fact, I think just about every diversion I’ve had for mechanical problems has been for something we did not train for.”

The FAA is working on guidance that stems from a 2013 working group report on flightpath management system usage that includes 18 recommendations. Much of the report’s focus is on how automation is both helping and hindering pilots. The anticipated guidance is expected to address several recommendations, including one on creating policy that airlines can integrate seamlessly into their own operations.

“The policy should highlight and stress that the responsibility for flightpath management remains with the pilots at all times,” the report says. “Focus the policy on flightpath management, rather than automated systems. Note that this policy would contain what has previously been named an ‘automation policy’ and would be broader, to emphasize flightpath management.”

Aviation Week & Space Technology April 8-21, 2019 page 26-28

[deltafox44]

I'm pretty sure that, as we learn more and more about the underlying issues, more people think just that, every day. I think a lot of us who have been following this closely will be surprised if the MAX gets back in the air quickly, with only a new software patch.
People got used to software updates... Windows needs updates after each security fault detected, Boeings need an update after each crash :ooh:

[Artus KG]

As edlb pointed out, there are some similarities. It is, however, a non max and a 12 sec AND trim.

wikipedia.org/wiki/Flydubai_Flight_981

[GordonR_Cape]

Woof woof, it's dark here....

So the dog that hasn't barked, as far as I know, is this:

Aside from the three-crew Lion Air flight that preceded the mishap flight, where are all the crews who might have experienced an AoA failure that triggered MCAS at flaps-up, and handled the situation safely?

For this to happen means that one of the AoA sensors has to be bad from the start, that it has to be bad enough to call a spurious stall warning, and it has to be the sensor that is driving MCAS on this flight (the last being a 50:50 chance). How often has this happened in the MAX's history? I have not seen a single such account in this long thread (I stand corrected if I missed one).

Clearly, that number would provide some valuable context to the two occurrences when the result has been fatal.

I agree that such data would be very useful, but suggest two reasons why it has not been forthcoming:
1. If AOA fails nose down (50% odds), there will be no stick shaker or stall warning or MCAS activation, and it would probably be a non event, written up for maintenance, or reported to the NASA hotline. Conversely if AOA fails nose up on the 'non-MCAS' side (25% odds), there will be stick shaker activation, but it will not be flight critical, and the fault will be repaired. In neither case will the airframe be examined in any detail.
2. In the event of AOA failing nose up and MCAS activating (25% odds), there is an overwhelming fatality rate. There are no known survivors other than the preceding Lion air flight, and unfortunately that airframe was destroyed the very next day, so there is little evidence to strip down and examine (apart from the FDR).
Does this provide some context on the relative scarcity of such occurrences?

[OldnGrounded]

People got used to software updates... Windows needs updates after each security fault detected, Boeings need an update after each crash :ooh:

Since we're at the stage where we can accept at least small injections of humor related to this deeply-depressing mess, here's an old one, which may be more amusing if you were a geek in a now-bygone computing world:

If Operating Systems Were Airlines (https://www.wired.com/1995/03/if-operating-systems-were-airlines/)

[pilot9250]

The isolation for MCAS is the STAB OFF switches beside pilots knee. Anything that moves the stab goes through these switches. But, you would have to recognize the problem. Clearly the pilots knew nothing about MCAS like the rest of us. All they may have seen is the STAB running AND - nose down.

The isolation for MCAS is reverse what it did then operate the switch before it does it again. Do that at high speed and low level while you're dealing with multiple critical warnings including IAS disagree, ALT disagree and stick shaker.

This is video game territory and I'm lost why we're still debating it.

Boeing are revising activation thresholds, adding signal redundancy, reducing maximum authority, updating the manual (FCOM, QRH and AMM) and adding training.

Why is anyone left debating whether the implementation of the automation is at fault?

[hans brinker]

Working for the B Team lately
Never was a Nr Man as in memorizing a heap of Pitch Pwr.
But I love Whatever It takes , then BallPark !
Let me give it guess:
94 N1 to say 70% N1 ca 240kts F5, ehhh. 1 to 2 units ANU say 1.5 ( Trim CHANGE)
Pure guess

Thanks! That doesn't sound too bad, I still think reducing power would have mead the situation easier to handle (yes, typing from my armchair)

[hans brinker]

Not sure about jumping into this 3300+ post thread but here goes:
I'm concerned about the crew's actions both for the manual trim attempt, and with the electrical trim attempts just before they lose control. And I can't help but distrust the inexperienced First Officer more.

To summarize:
- they had the MCAS pitch control problems
- got the Cut-out switches to stop MCAS from trimming down any more
- they're flying OK, got some altitude banked, although still in crisis mode, still having to hold back pressure, deal with the one stick shaker, overspeed clackers after some point, and what not
- there's a discussion about the manual trim not working. We don't know the exact words used.
- Interpretation: Might have to do with high forces on the manual trim wheel, but it is also unclear whether the First Officer really doing what was expected. Was he just hitting the thumb trim switch, or trying to roll the trim wheel (without much experiences of the forces that might be involved) or did he actually have the fold-out handle open and still find he was unable to turn it?
- either way, they keep flying OK for another minute or so
- then there are the 2 very short electrical up trim attempts (as others have also commented on). I agree that the graphs show a small up trim effect. Hard to see on the graph but really does look like a little bit of nose up trim change. Barring any totally unexpected electrical issue, this is only possible with electric trim turned back on!
- very soon after, MCAS kicks in, trimming a bunch nose low, and the pilots lose control and nose over.

The preliminary report gives no indication that the pilots discussed turning electric trim back on. Nothing about, "Despite the AD saying to leave it off, you turn electric trim back on, I'll trim out these awful control forces, you turn it back off before this thing tries to pitch down again."
Did the Captain try turning it back on? Or was the First Officer fiddling around on his own? Trim gets turned back on with no consultation and but only 2 ineffective short trim activations are made. Were jackscrew forces so high that electric trim wasn't working well? Who knows, I'll leave that to the experts. But the electric trim attempts were two short blips, not like trying mashing that button down a full 5 seconds to see if they got some effect out of it.

That really messed them up, ineffective trim attempts without killing the electric trim system again afterwards.

So, before you bad mouth the FO, AFAIK he was the one suggesting using the stab cut out switches, inhibiting the third MCAS input. We don't know who switched the trim back on, or who made the insufficient inputs close to the crash, so if I were you I would give it a rest.

[hans brinker]

68 tons of -800 at 10000 ft with FL5 and 240 kts will need about 72-73% N1, but the trim will stay around 4 units.
I don't think you'll ever see the trim near full AND during normal ops.

Thanks, and as replied already by mana, it was the change, not the absolute value.

[hans brinker]

I don’t fly the 737 Max, but after doing a bit of ‘what-if-ing’, I’ve come to the conclusion that if I were a Max pilot and had stick shaker on take-off, I would not fully retract the flaps. I would retract to Flaps 1. My experience on other Boeing’s (767 & 744) is that Flaps 1 provides the best manoeuvre margin to the stall and in the 737 Max would prevent MCAS doing it’s (evil) thing.

Yeah, considering they switched the trim off, it sounds like they were aware of what was happening as far as trim. However they never reduced power and going 350kts with the flaps out is probably going to end bad too.

[hans brinker]

Attempted level was FL320 !

With stall warning and attempting to clear the terrain, more speed means more potential energy, so I think overspeed was not on top of their priorities.

If Boeing NNC for trim runaway had included "reduce speed if manual trimming is too hard", perhaps they would have done it...

They set a lower alt in the window, so not trying to climb to F320

[positiverate20]

The nose up moment of the engines thrust may be important at lower speeds, but negligible at higher speeds, since the thrust is constant but any other aerodynamic moments vary as the square of speed.

What about the pitch of airbrakes ?

🧐

Thrust also varies as a square of speed?!

Acceleration is "metres per second squared"

I think I see where you may be trying to come from... thrust and drag are balancing out, increasing thrust will result in an ever decreasing change in velocity. (Or less acceleration)

But if you agree with this, you must also accept... in that state, a marginal reduction in thrust will result in an ever increasing change in velocity? (Or more deceleration)

My point is, doesn't matter where on the scale you want to pick, drag and thrust are always going to be proportional to eachother.

[TLB]

Yeah, considering they switched the trim off, it sounds like they were aware of what was happening as far as trim. However they never reduced power and going 350kts with the flaps out is probably going to end bad too.

Don't know what you mean by "flaps out" hans brinker. If you mean the flaps were 'down', they were not. The flaps were up. If they were down, the MCAS would not have activated.

[Gegenbeispiel]

>"Firing blanks"

That's not uncommon in avionics software. It simplifies code - and that, more often than not, makes it more reliable. Plus, the not-engaged FCC is then a hot spare, ready to engage without further logic.

[Airbubba]

Attempted level was FL320 !

From the narrative excerpted above:

At 05:41:21, the selected altitude was changed from 32000 ft to 14000 ft.

Addis airport elevation is 7657 feet.

If Boeing NNC for trim runaway had included "reduce speed if manual trimming is too hard", perhaps they would have done it..

Or if it said 'don't forget to fly the plane!' Avoiding the overspeed by reducing power is pretty basic in my opinion.

[Gegenbeispiel]

Does anyone else think that maybe the very fact that they're trying to solve this through a software update may be part of the problem?

Since the MCAS is just software (running in the FCCs) there is no other way.

[hans brinker]

Don't know what you mean by "flaps out" hans brinker. If you mean the flaps were 'down', they were not. The flaps were up. If they were down, the MCAS would not have activated.

Yes, I should have said down, but was a direct reply to someone suggesting he would have left the flaps F1 in this situation, and seeing as we are up to 3000+ post already I would suggest you read before you post, so we don't get endless back and forth like this.

[Loose rivets]

I'm trying to read every post, so forgive if covered...

I'm not sure how microscopically detailed the data readouts are, but re the two blips of ANU which were not continued - Is it conceivable that PF was alarmed at the momentary high g due to excessive speed?

Over the last weeks I've not really been able to assess the captain's likely abilities during what must have been very demanding moments. Even gums has said he's not sure he'd have cottoned on to what was going on right away. I can well imagine the shaker, plus speed etc., causing the STS movements to blur with the intermittent MCAS rotations.

A recent poster mentioned a blip about every ten knots to counter the STS. That surprised me and shows the perfectly normal activity of the wheel in this phase.

As one who loved things going TU to make the day more interesting, I have to confess my 25 minutes with the stick-shaker going at 2000' in inky black chop really tested my ability to shut out what we quickly deemed to be a false warning. It was as though the warning was fighting to get past all reasoning. I recall my concentration giving an element of tunnel vision. I'm told it's a bog-standard human reaction but I doubt it would cut out the white patch of the wheel flashing by.
.
.

[Sunfish]

They are not “near together” the landing gear geometry is established by the sweep of the wings and the chord at fuselage join. The LG trunnions bearing is as close as physically practical to the intersection of the rear spar and MLG beam.

The b737 track is 5.7m. The A320 is 7.59m. So what? Astonishing? Since when has the B737 had a problem with scraped nacelles or crosswinds?

As has been explained by people with real B737 experience, the manual trim is very, very stiff to move when loaded at speed to the point that special technique is required - and that is assuming you even understand what the problem is in the first place - which they couldn’t since MCAS wasn’t on the training syllabus.

The MCAS put the aircraft into an almost (or totally) unrecoverable situation at low altitude and no BS about untrained inexperienced pilots is worth a pinch of rocking horse poo.

Try using any highly automated vehicle and see how YOU like it when something fails, even if you are on top of your game, the environment can get very confusing very fast. The B737 is supposed to be designed to be operated safely by the average commercial jet pilot and achieve the advertised performance when flown by said average pilot obeying the manufacturers instructions. Clearly Boeing has totally failed to do this in the latest variant of the 737 design.

As for the “new airplane” mob. It is difficult to understand how a redesign is going to make more than incremental changes to the basic B737 design. The design problem remains the same - which is why the A320 looks something like a 737. Fuselage cross section and engine position govern pretty much everything.

[Bend alot]

Since the MCAS is just software (running in the FCCs) there is no other way.

My understanding is MCAS is only required for compliance of a regulation, and it can not be compliant due to lift from the engine cowlings during certain stages of flight without MCAS.

So the regulations could be looked at to see if still relevant, the engine cowlings could be modified or adjusted so lift is not happening in that stage of flight or the AOA interface be modified.

A software patch alone will not pass the pub test.

[WingNut60]

My understanding is MCAS is only required for compliance of a regulation, and it can not be compliant due to lift from the engine cowlings during certain stages of flight without MCAS.

So the regulations could be looked at to see if still relevant, the engine cowlings could be modified or adjusted so lift is not happening in that stage of flight or the AOA interface be modified.

A software patch alone will not pass the pub test.

The trouble, for Boeing, with that is that it may well cause an increase in drag, as would rear fuselage strakes.
Maybe minor, maybe not so.

[73qanda]

Originally Posted by onsoutherntip https://www.pprune.org/rumours-news/images/buttons/viewpost.gif (https://www.pprune.org/rumours-news/showthread.php?p=10439518#post10439518)
I am curious as to where the FDR data for the stabilizer trim is read from - yoke trim switches or the motor drive electronics? Most high power motor drives have feedback that detects if the power demand is exceeded. If this happens, power to the motor is disabled, in order to protect it. Therefore a situation could arise where even though the pilot is activating ANU trim, it results in just a short ANU motor movement, before the motor power limit is exceeded. So if the FDR records from the drive electronics, the trim ANU 'request' by the pilot, will be seen as just a 'blip' although the trim switch is still activated,

This would account for AND trim running the full period as motor power demand is not exceeded (low aerodynamic load), but ANU trim is fighting against high aerodynamic load, which activates the motor protection. Thoughts?
I have been thinking the same thing since the preliminary came out but with less Engineering knowledge than you hadn’t come to such a clear position.
I was just thinking “ I bet they were trimming nose up but the FDR only recorded what the screw jack did” without any systems knowledge to explain how that may be the case.

[Bend alot]

The trouble, for Boeing, with that is that it may well cause an increase in drag, as would rear fuselage strakes.
Maybe minor, maybe not so.

I think the problem for Boeing is they had a mechanical problem they tried to fix electronically, but badly and on the sly.

[ATC Watcher]

I continue to find it disturbing and surprising that more than a few posts are focused on blaming, or at least strongly suspecting, crew error as a primary cause of the Ethiopian crash.

Surely, it should be clear, from all we have learned and discussed in the weeks since that accident, that the crew was faced with a situation that almost any crew would have found very difficult, if not impossible, to deal with successfully. If mistakes were made, they were made in an environment where not making mistakes was extremely unlikely and in which they would never have found themselves if the OEM and the regulatory authority had not made fundamental and extraordinary mistakes in designing and certifying the aircraft. And those entities weren't facing imminent sudden death when they screwed up.
I share exactly the same feelings, too many armchairs pilots ( and even non-pilots) here telling us what the crew should have done KNOWING THE FULL SITUATION IN ADVANCE.
Having myself unfortunately been through an accident , the first thing that comes to your mind is understanding what is happening and this takes a certain time to process . Your mind is rushing at 120% and things like FORDEC and DODAR are not the first things that come to your mind.., and hearing people telling me afterwards what I should have done was not helping at all. A bit of respect for the guys faced with horns , bells and Christmas trees thrown at you unexpectedly. A final remark to those advocating a reduction of power, come on after a stall warning (stick shaker) at less than 1000 Ft AGL ? , or course you will level off and keep the power ,I would argue in ANY airplane, but I am not flying 737s ...After that depends how your mind is prioritizing..

[73qanda]

A few contributors have suggested that they very quickly would have applied the Airspeed Unreliable memory items. ( flight directors off, 10 degrees NU and 80% thrust on the NG) . I think that the confusion when presented with a lot of information in a short space of time in a dynamic situation is often underestimated. It takes time to process information, and then more time to conclude its meaning and decide on a course of action. Salience is often key and I suspect that the stick shaker had it in spades. If the stick shaker did initially consume much of the Captains cognitive capability, then reducing thrust may not have been seen as a wise choice so close to the ground, with an inability to lower the nose much just after rotate the next pertinent step is to increase thrust if the stick shaker is valid.Confusion already in the first second or two is possible/probable.
Edited to add: ATC WATCHER I posted the above simultaneously as you posted with pretty much the same sentiment but without having read your post.

[George Glass]

It is not being wise after the fact to point out that this event was mis-handled as soon as the aircraft is airborne.
Liftoff is at 05:38:39
L/H stickshaker activates almost immediately. ( Birdstrike?)
Captains first attempt to engage autopilot is at about 400 ft AGL.
It doesn’t engage but after several attempts appears to have engaged till just after flap retraction at 05:39:45
MCAS cannot have been an issue till then, 1:06 after becoming airborne.
Engaging an autopilot with stickshaker active at 400 feet is a seriously bad idea.
It is not second guessing to say that at that point flying an attitude and thrust setting would have been the wisest option.
Startle factor is huge. I’ve been there. But that’s where you justify your pay check.

[Albino]

KNOWING THE FULL SITUATION IN ADVANCE.

Were the crew unaware of the Lionair crash and the bulletin released by Boeing? How did this situation differ from that one in respect of MCAS activation?

It's an interesting point whether the stab readout is taken from what is commanded or the position of the jack. Considering the AND command is registered without stab movement I suspect it is demand, it's how the narrative reads as well.

Ethiopian have played a blinder IMO. By making their press release before the initial report media around the world are reporting that the crew repeatedly followed procedures, BBC are still highlighting this point. From the data released memory items for Airspeed Unreliable were not actioned, the aircraft was not controlled with pitch AND trim as per the Unscheduled Stab Trim memory items. Nobody has questioned the validity of this statement.

[73qanda]

I understand what you are saying GG and I agree that engaging A/P is not the way to go about solving problems like this, I also agree that an attitude and thrust setting is where you want to end up in this situation, however, between sensing the stick shaker, recognising it’s meaning, reassessing the airspeed, maybe glancing at the flap indicator, sensing that there are other warnings occurring and deciding not to lower the nose as per the memory items because it may be a false stick shaker, time will pass, how much time? As I said, I think some posters are underestimating how much time would pass before they reduced thrust that close to the ground.

[Vinnie Boombatz]

https://ecfr.io/Title-14/se14.3.121_1344

"§121.344 Digital flight data recorders for transport category airplanes.

(a) . . . The operational parameters required to be recorded by digital flight data recorders required by this section are as follows: . . .

. . . (19) Pitch trim surface position or parameters of paragraph (a)(82) of this section if currently recorded;

. . . (82) Cockpit trim control input position—pitch . . . "

So toss a coin. With help from Boeing and the carrier(s), the investigators should be able to determine the signal source.

[George Glass]

73,
I’ll predict that one of major findings in both of these accidents is that everybody forgot just to fly the aircraft.
The B737 is a very simple aircraft with lots of bells and whistles, most of which are nice to have, not must have.
An enthusiastic Boeing instructor once took me to 35,000 ft in the simulator at the end of a training session then reached up to the overhead panel and turned everything off.
The aircraft still flew.
Dont think they do much of that stuff anymore.

[Capn Bloggs]

It's an interesting point whether the stab readout is taken from what is commanded or the position of the jack. Considering the AND command is registered without stab movement I suspect it is demand, it's how the narrative reads as well.

No, the chart clearly shows the pitch trim "command" and then the line below is the actual trim position. It even says "automatic trim command with no change in pitch trim".

I’ll predict that one of major findings in both of these accidents is that everybody forgot just to fly the aircraft.
And I'll predict that I and I'm sure many others will say "they were never trained to fly the aircraft". You can't forget what you didn't know.

[KRUSTY 34]

73,
I’ll predict that one of major findings in both of these accidents is that everybody forgot just to fly the aircraft.
The B737 is a very simple aircraft with lots of bells and whistles, most of which are nice to have, not must have.
An enthusiastic Boeing instructor once took me to 35,000 ft in the simulator at the end of a training session then reached up to the overhead panel and turned everything off.
The aircraft still flew.
Dont think they do much of that stuff anymore.

I hear what you’re saying George, and I concur 100%. Except for one apparent wild card...

MCAS!

[Majorbyte]

This constant assumption by aircraft manufacturers that the pilots don't know f*** all about flying and insist on installing complicated systems to act as a safety pilot is crazy, how often do pilots stall airliners?? very very rarely is the answer, and if they were stupid enough to stall the aircraft, recovery is relatively simple, assuming some altitude is available. A message to Boeing and Airbus, please let the pilots fly the aicraft you build and stop confusing them with unnecessary and untimately dangerous technology.

[groundbum]

so will the software fix, and slightly updated training, be enough to get the MAX back into revenue service?

I predict after ET not. It's apparent even with MCAS turned off, the cockpit does not return to peace and tranquility where average ability pilots can regain control and land. It's apparent from the ET interim report that a lot more was going on in the cockpit, and that was it was beyond the two pilots to get it back together, mainly due to excess speed and aerodynamic forces making proper trim next to impossible without some, as yet, untrained yoyo, manoeuvre.

I would suggest no regulator would be willing to pass the MAX back into service based on a patch and minor training update.

G

[Capn Bloggs]

the aircraft was not controlled with pitch AND trim as per the Unscheduled Stab Trim memory items. Nobody has questioned the validity of this statement.
Nothing in the Memory items like that (as per the report, page 30). If the runaway continues after AP is switched off, is says to switch off the trim. Nothing about "counter trim with control column switches, return aircraft to pitch neutral then switch off trim" as you are alluding to. And even if they had "disengaged the autothrottle", what would that have achieved? Nothing unless you then pull off a fistful of thrust...

Then you pull out the two page AD memo from Boeing and recall what it said: at the bottom of page two "Electric stabiliser trim can be used to neutralise...".

[Freehills]

73,
I’ll predict that one of major findings in both of these accidents is that everybody forgot just to fly the aircraft.
The B737 is a very simple aircraft with lots of bells and whistles, most of which are nice to have, not must have.
An enthusiastic Boeing instructor once took me to 35,000 ft in the simulator at the end of a training session then reached up to the overhead panel and turned everything off.
The aircraft still flew.
Dont think they do much of that stuff anymore.

mr picky points out that you mean the simulator kept on simulating. Not quite the same thing as a copilot doing that in flight.

[alf5071h]

73qanda, ATCWhatcher,

:ok: putting the event in context and human factors :ok:

also with, onsoutherntip re interpretation of FDR trim command and tail trim movement - they may differ; see post https://www.pprune.org/10440231-post27.html and the back links.

Adding to some of the ‘historic’ concerns, would the slightly smaller trim wheel in latter versions of the 737 reduce the effective torque which could be applied in grabbing the wheel as part of the runaway trim drill - and applying manual trim to recover ?

[Sunfish]

For the benefit of the “MCAS is just there to satisfy a paper regulation” mob; the aircraft control characteristics regulations require that the stick force increase with increasing attitude. This is not a “paper regulation” but a real world need for the change in attitude to be proportional to force in other words the required control inputs as applied by the pilots don’t reduce or worse reverse with changes in attitude.

To put that in automotive terms some of you might understand; oversteer is not allowed.

[pontifex]

I have grown slightly cross eyed following the huge volume of posts concerning the tragic events with the 737 MAX. One item that seems to have been mentioned just once (or thereabouts) is that things only started to go pear shaped immediately following flap retraction. Surely the clue should have been obvious to any adequate pilot and the previous configuration restored. As far as I understand things that would have saved the day. I have done a fair amount of 737 work but that was back in the day when they worked like normal aeroplanes (737 200& 400) so I may be wrong. This principle, however, has saved my life twice and I don't pretend to be anything other than an average operator. Am I wrong?

[astonmartin]

They set a lower alt in the window, so not trying to climb to F320
But they stayed in ‘level change’ mode all the time. That means that the autothrottle kept the engines at climb thrust all the time.

Both altitude and speed were uncontrolled.

[Albino]

Nothing in the Memory items like that (as per the report, page 30). If the runaway continues after AP is switched off, is says to switch off the trim. Nothing about "counter trim with control column switches, return aircraft to pitch neutral then switch off trim" as you are alluding to. And even if they had "disengaged the autothrottle", what would that have achieved? Nothing unless you then pull off a fistful of thrust...

Then you pull out the two page AD memo from Boeing and recall what it said: at the bottom of page two "Electric stabiliser trim can be used to neutralise...".

You need to go and read step 2 again. It wasn't completed, at any point after the MCAS AND.

What would disconnecting the autothrottle have achieved? Well you could set thrust to something more sensible and fly the aircraft.

You mean page 2 of the memo that gave specific operating instructions to crew? It even included a note (obvious to most with any common sense!) to put the aircraft in trim, then cut out the stabs.

[Vinnie Boombatz]

Interesting that media have not interviewed the survivor crew. Maybe Boeing financed some scholarships for their kids?
They could provide first hand descriptions of what was going on, and how hard it was to deal with it.

Edmund


The Indonesian preliminary report (https://knkt.dephub.go.id/knkt/ntsc_aviation/baru/pre/2018/2018%20-%20035%20-%20PK-LQP%20Preliminary%20Report.pdf), para. 1.18.1, starting on pg. 19 (pg. 28 of PDF), has a narrative of the flight prior to the Lion Air accident.

The FDR data for that flight is plotted as Fig. 7 on pg. 16 (pg. 25 of PDF). The time scale is a bit odd (about 11 minutes 10 seconds per major division), and there are no numbers on most of the vertical axes.

The plot is also for the whole flight, although dealing with MCAS occurs over about 10 minutes very early in the climb. Hence the scale makes it hard to see the details of that portion.

https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/1057x545/jt43_trim_0111b88ee6f51cfa4f96ceb762084ebccc67057c.jpg
portion of FIg. 7 from Indonesian report

Here are vertical velocity and altitude plots of ADS-B data for that flight made using data (https://blog.flightradar24.com/blog/wp-content/uploads/2018/10/JT43-Granular-ADS-B-Data.csv) posted on-line by FlightRadar24 (https://www.flightradar24.com/blog/flightradar24-data-regarding-lion-air-flight-jt610/).

https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/584x341/jt43_vertical_velocity_16393a6a7a885b84da29ef9163be4fc9e3051 d96.jpg

https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/583x345/jt43_altitude_0692c2fae8758211ec9f9ee846727ba0bcc0468f.jpg

There are quite a few cycles of MCAS activation before the pilot cut out the stab trim, with one really steep descent. The bottom of that descent is about where the FO made the first PAN PAN call, per the narrative.

[GordonR_Cape]

I have grown slightly cross eyed following the huge volume of posts concerning the tragic events with the 737 MAX. One item that seems to have been mentioned just once (or thereabouts) is that things only started to go pear shaped immediately following flap retraction. Surely the clue should have been obvious to any adequate pilot and the previous configuration restored. As far as I understand things that would have saved the day. I have done a fair amount of 737 work but that was back in the day when they worked like normal aeroplanes (737 200& 400) so I may be wrong. This principle, however, has saved my life twice and I don't pretend to be anything other than an average operator. Am I wrong?

AFAIK the captain was focused on the autopilot around the time of flaps retraction, and the co-pilot was the one who made the correct call to hit the trim cutoff switches. That should have saved them, if all the right procedures had been followed timeously. Unfortunately neither thought to reduce the airspeed, which could have unloaded the horizontal stabiliser and permitted manual trimming, until it was much too late for any further options.

[FullWings]

From one of the media reports:
...“If I had been flying a MAX with stickshaker activation at liftoff after the Lion Air accident, shutting off the trim would have been accomplished in a matter of seconds, not minutes,” says one U.S.-based MAX pilot. “I probably would have activated the stabilizer trim cutout switches before the gear was even up. Why that didn’t happen on the Ethiopian flight is a mystery to me.”
So, this MAX pilot’s first response to a stall warning (which could be genuine) is to deactivate the trim. This is a terrible indictment of the awful kludge which the airframe and control systems are on the MAX, that something like an incipient low-level stall comes second in priority to MCAS. The even sillier thing is that if it was a genuine stick shake, you’ve now disabled the system that was going to help you recover... :rolleyes:

[coaldemon]

I feel for the crew in these circumstances as they appear to have been overloaded to the extreme. Everyone is looking back with hindsight but a couple of things that I have seen in the Preliminary report:
1. It looks like a bird has hit and sheared off the AoA vane. It settles at 75 degrees Up and the aircraft is 15 nose up so the counterweight is holding it down. Then repeatedly trying to put in the Autopilot with Stick shaker going was only going to make a bad situation go even worse. Not a recommended procedure I have found anywhere in the Boeing Manuals for any aircraft. Very similar to a Ryanair event a few years ago in an 800. Crew manually flew it around and landed it.
2. I can't see where any complete checklists were done. None at all. Just the Stab Trim cut-outs thrown to cut-off by the FO when the Captain was trimming the aircraft back to neutral. If the FO had waited for the call for the checklist and actioned it with the Captain they may have been in a better position closer to neutral. Remember that MCAS in the old software form stops when you start to trim it back with the electric trim. When you stop you have 5 seconds so then is a good time to do the checklist and throw the switches. From what I can see there were two full applications of MCAS prior to them putting the Stab motors back on.
3. It appears that while in manual mode the Stab was trimmed even further nose down. I think this may have been inadvertent by the FO but made a bad situation even worse. It also made it more difficult to then manually trim back and they gave up. As someone has already mentioned you need to put a lot of force (around 50 lbs from memory) and have some coordination to wind it back at high speed. Or you pull the power back and slow down which brings us to
4. The Take off power was not at any stage pulled back and they went through VMO within about 2 minutes. From there they kept accelerating. All the way to 500 kts
5. Then to put the system back to normal then meant that MCAS was still inputting to the circuit. That was it. No chance of recovery

One of the things that Manufacturers need to realise is that a lot of their customers do not have English as their first language. (Frankly some of the Airbus manuals I have had to read with Franglish take this to another level as well). If the guys had read all the info on MCAS and understood it would things have been different? With stick shaker going on during departure in the Heavier machines you never select flaps up until you confirm what has happened and you are well clear of terrain. To take the Flaps up at 1000 ft in this situation knowing that the shaker was going was an interesting move most likely reflex to the quickly accelerating aircraft.

As someone else has said that is why Airline Crew get paid well and why training should be more about the things that will cause you large harm and how you react rather than some of the tick the box exercises.

Does the aircraft need to be redesigned. Nope. The software does need to be changed and Boeing need to be a lot more rigorous in how they approach these critical systems. I have flown the MAX and it is a nice aircraft to fly. Lets see where the media take the world with this one.

[KRH270/12]

From one of the media reports:

So, this MAX pilot’s first response to a stall warning (which could be genuine) is to deactivate the trim. This is a terrible indictment of the awful kludge which the airframe and control systems are on the MAX, that something like an incipient low-level stall comes second in priority to MCAS. The even sillier thing is that if it was a genuine stick shake, you’ve now disabled the system that was going to help you recover... :rolleyes:

So true! And with the flaps extended there is no need to worry about MCAS.

But still the Most important question is:

Why did they not use electric Stab trim to get back into an in trim condition without any control column pitch forces and then Hit the cutout switches???

[EDLB]

so will the software fix, and slightly updated training, be enough to get the MAX back into revenue service?

I predict after ET not. It's apparent even with MCAS turned off, the cockpit does not return to peace and tranquility where average ability pilots can regain control and land. It's apparent from the ET interim report that a lot more was going on in the cockpit, and that was it was beyond the two pilots to get it back together, mainly due to excess speed and aerodynamic forces making proper trim next to impossible without some, as yet, untrained yoyo, manoeuvre.

I would suggest no regulator would be willing to pass the MAX back into service based on a patch and minor training update.

G
+1

The 737 safety philosophy means that it turns into a conventional stick and rudder aircraft once you turn the AP off. And that with redundant left and right seat set of controls. The PF assumes in AP off mode that he has full authority on the flight controls and surfaces. There are automatic flap retract in over speed left but that does not reduce his controll over the aircraft.
If you brake that philosophy by introducing “features” overriding PF control inputs they need to be full FBW worth with all fail safe features needed for a FBW control.
I do not see how Boeing can implement that easily into the 737 MAX.

With the two accidents it came out, that the manual trim wheel can not be actuated manually in a high elevator deflection and high speed situation. That aerobatic manovering is the cure for that can unlikely be certified for a transport category aircraft.
With 50 years of 737 operation that was not a big problem because nobody was as stupid as the MCAS system and gave full 5 seconds of AND trim in an already peculiar nose down situation close to the ground.

In a fighter jet in such a case you might invert the aircraft and rollercoaster the stuck trim out. But that is not a solution for a transport category aircraft.

[SLF3]

Only The opinion of SLF, but the issue is not MCAS. The issue is the position of the engine relative to the wing. MCAS is a bandaid on an open wound to get around a rational regulatory requirement.

Boeing should not have proposed the Max, and the FAA should not have accepted it. It is a fundamentally flawed design.

i remember reading an article when the neo was announced which postulated that Boeing would not be able to match it with an upgrade of the 737 because it would require a redesign of the undercarriage to get the necessary ground clearance for the engines. So the design issue was obvious to that much maligned species, a journalist, from the start. Boeing and the FAA knew.

This goes way beyond MCAS. It is about the engineering conscience of Boeing and the independence and competence of the FAA.

[SMT Member]

Let's not forget why MCAS was born: To make the Max feel the same as the NG at the extreme end of the envelope, thus allowing for a common type rating and 1-hour CBT conversion course. This in turn allowed Boeing to use the common rating as a marketing tool.

There are rumours afloat, that the contracted Boeing signed with SW had a clause saying Boeing would pay SW 1 million USD for every aircraft delivered, if sim training was necessary to convert from NG to Max. That's 280 million good reasons why a bean counter and lawyer driven company would come up with an idea such as MCAS.

To my mind there is 'simple' set of possible solutions to this problem:

1: Ditch MCAS
2: Restore stability and stall characteristics to an acceptable level through sound aerodynamic means
3: Forget about the common type rating; this is not your grandfathers 737 so stop pretending it is

[Airbanda]

Woof woof, it's dark here....

So the dog that hasn't barked, as far as I know, is this:

Aside from the three-crew Lion Air flight that preceded the mishap flight, where are all the crews who might have experienced an AoA failure that triggered MCAS at flaps-up, and handled the situation safely?

For this to happen means that one of the AoA sensors has to be bad from the start, that it has to be bad enough to call a spurious stall warning, and it has to be the sensor that is driving MCAS on this flight (the last being a 50:50 chance). How often has this happened in the MAX's history? I have not seen a single such account in this long thread (I stand corrected if I missed one).

Clearly, that number would provide some valuable context to the two occurrences when the result has been fatal.

Was about to post same question. Have other incidents been reported?

[bill fly]

Can anybody report whether any kind of functionality checks are being performed on the grounded fleet?
eg. Wiring/ FOD/ AoA etc. Plenty of time now for that..

[Gegenbeispiel]

The B737 is a very simple aircraft with lots of bells and whistles, most of which are nice to have, not must have.


The original B737 may have been that, the MAX is not. If it were. you wouldn't need MCAS to certify.
AFAIK, the MAX is certified as a B737 amendment. That may be wrong. If MCAS is necessary to certify, the aerodynamics are radically different.

[Derfred]

Was about to post same question. Have other incidents been reported?

Well, one was, just a few minutes ago:

I’ve had a false stick shaker on the B737 during rotation at take-off once. I agree with others that this is a huge distractor. After confirming that it is false, and change of controls, it is not only distracting, but also annoying.

The poster hasn’t stated what caused the stick shaker at rotation, it could have been rogue AOA, but it could also have been something else.

Also didn’t state whether it was a MAX and caused MCAS.

[DaveReidUK]

they went through VMO within about 2 minutes. From there they kept accelerating. All the way to 500 kts

No, they didn't "keep accelerating". They flew at or around Vmo for almost 3 minutes. It was only in the last 30 seconds of the flight, as they were rapidly losing altitude, that airspeed got anywhere near 500 kts.

[George Glass]

Gergen,
I beg to differ. MCAS is only there to ensure the control column force required to increase pitch does not decrease at high angles of attack.
It is a certification requirement. The aircraft will fly perfectly happily without it.
Disconnect and fly the aircraft.

[abdunbar]

+1

The 737 safety philosophy means that it turns into a conventional stick and rudder aircraft once you turn the AP off. And that with redundant left and right seat set of controls. The PF assumes in AP off mode that he has full authority on the flight controls and surfaces. There are automatic flap retract in over speed left but that does not reduce his controll over the aircraft.
If you brake that philosophy by introducing “features” overriding PF control inputs they need to be full FBW worth with all fail safe features needed for a FBW control.


With the two accidents it came out, that the manual trim wheel can not be actuated manually in a high elevator deflection and high speed situation.



Your first point is the heart of the matter. When faced with any aircraft control problem, the pilot needs to be able to quickly revert the aircraft to a configuration in which he knows what he is dealing with. In the old style mechanically controlled planes such as the 737, this was easily achieved with the autopilot disconnect button. Further, old guys like myself, grew up with these systems. I started flying transport category aircraft when an autopilot was simply a wing leveler and pitch or altitude hold. Manual flight was routine for climbs and descents. My generation needed to be encouraged to embrace auto flight as it matured. We were spring loaded to dump it and manually fly if we got behind. As the years moved on we started to have new/younger pilots whose only experience was systems, auto flight and flight management computers that could handle all phases of flight except initial takeoff. We were encouraged to use these systems fully to reduce workload and to increase our ability to maintain a lookout for traffic, terrain, volcanic cloud, cb, whatever. This advancement was wonderful but it also came with a problem. Over time, hand flying skill and instrument scan was degraded, especially in those who did not have a lot of experience hand flying in vertigo and anxiety inducing circumstances. This resulted in a disability where autoflight could, depending on the individual, become a crutch rather than a tool. The pilot with this disability needed, in any crisis, to first get auto flight operating. This is not a big problem in most circumstances but is a very big problem when the issue is basic aircraft control.

To your second point. I do not know if this is a fact and it seems like it should have been a certification issue if it is. I would not accept any simulator demonstration but would expect that it has been demonstrated in the actual aircraft that the manual, hand crank, stab trim is operable throughout the envelope of the aircraft, speed up to Vmo, altitude, thrust setting, g loading, Cg. If this was not done, it is a problem. If there is a speed limit to manual stab operation, the pilots should be told, even it is just a note that it was not demonstrated to work in excess of Vmo , or whatever speed it was tested to.

[Richard C]

Well, one was, just a few minutes ago:



The poster hasn’t stated what caused the stick shaker at rotation, it could have been rogue AOA, but it could also have been something else.

Also didn’t state whether it was a MAX and caused MCAS.

If you had the shaker on rotate, you wouldn't be raising the flaps in a hurry so at least MCAS wouldn't start retrimming the plane at low altitude.

[MemberBerry]

You need to go and read step 2 again. It wasn't completed, at any point after the MCAS AND.

One could argue that you can skip step 2 when the A/P is not engaged.

I don't think the runway stabilizer memory items cover all possible runway situations properly, especially when MCAS is involved. A step 2.5 asking you to try to bring the trim back to neutral using the thumb switches, before applying the cutoff switches, wouldn't hurt, in my opinion.

And having in mind that the current version of MCAS will re-activate in 5 seconds, it should also tell you to use the cutoff switches as soon as possible after you bring the trim to neutral, in under 5 seconds after your last electric trim use. With the new MCAS version that will hopefully no longer be needed.

There are plenty of things the accident crew could have done better, and they clearly made mistakes. I think using the cutoff switches before bringing the trim to neutral was one of their smallest mistakes, if you can even consider it a mistake.

Boeing and the FAA claiming, after the Lion Air crash, that the existing procedures for dealing with a runway stabilizer are sufficient to address the MCAS issues is a much larger mistake, in my opinion.

And the elephant in the room is that manual trimming with the trim wheels can be extremely hard, or even impossible to do, when you apply a lot of nose up elevator depending on the airspeed.

In addition to the MCAS fixes, I think this is one of the problems the FAA and Boeing need to address, not only for the MAX, but for previous models as well.

Unfortunately I don't see an easy solution for that particular problem. Some complex changes might be needed. For example an additional electric trim circuit and motor as a backup for the main one.

[Richard C]

Gergen,
I beg to differ. MCAS is only there to ensure the control column force required to increase pitch does not decrease at high angles of attack.
It is a certification requirement. The aircraft will fly perfectly happily without it.
Disconnect and fly the aircraft.

That seems to be the problem - you can't disconnect MCAS without defeating the trim motors and there now appears (from the ET report) to be a problem in retrimming manually with a lot of back-stick. The other way would be to run down a stage of flap, which should stop MCAS interfering but it's hard to see a procedure which called for that getting approval.

[Derfred]

One could argue that you can skip step 2 when the A/P is not engaged.

Seriously?

Aircraft is trimming badly forward when you don’t want it to. Try trimming it back then trim cutout. If that doesn’t work then trim cutout anyway. You’re a pilot.

[MemberBerry]

Seriously?

Aircraft is trimming badly forward when you don’t want it to. Try trimming it back then trim cutout. If that doesn’t work then trim cutout anyway. You’re a pilot.








I'm not saying it's a correct argument, personally I don't think you should skip step 2, but I've seen some people arguing that. So there is some confusion about those memory items.

But, in any case, the problem is you have only 5 seconds to use the cutout switches before MCAS does it again. If you delay that by only a few seconds, you end up with an out of trim aircraft. No matter how you look at it, that is not ideal.

And the Ethiopian crew did trim it back partially before using the cutout switches. They probably felt the trim they applied was sufficient to make the aircraft controllable enough at that point, and didn't want to risk applying more with the stick shaker active.

And assuming it's not MCAS, but a regular trim runaway that can't be stopped or reversed with the thumb switches, you will be out of trim after using the cutout switches. Both on the MAX and also on older models. Not easily being able to then correct the trim with the trim wheels in that situation is a big problem.

My point is that, even if you don't skip step 2, and I don't think you should skip it, you can end up in the same situation they did, depending on the type of runaway you are experiencing.

[gmx]

2. In the event of AOA failing nose up and MCAS activating (25% odds), there is an overwhelming fatality rate. There are no known survivors other than the preceding Lion air flight, and unfortunately that airframe was destroyed the very next day, so there is little evidence to strip down and examine (apart from the FDR).
Does this provide some context on the relative scarcity of such occurrences?
​​​​​​A disconcerting mystery is why the crew of the preceding LionAir flight didn't feel like they had miraculously dodged an insidious malfunction, and instead handed the aircraft to the next crew with little warning of the mortal danger that lay ahead. And why the airline allowed the vehicle back into the air after an emergency had been declared on that preceding flight, without fully understanding the nature and source of the flight control issues experienced.

For some reason I'm less concerned about the automated flight control issue than the fragility of the safety processes enacted in the event of a declared emergency. If that Lion aircraft had been grounded immediately following the pre-accident flight ...

[Albino]

One could argue that you can skip step 2 when the A/P is not engaged.

Just to confirm, I'm talking about 'Control airplane pitch manually with control column and main electric trim as needed'

This is pretty basic stuff.

[Ian W]

I agree that such data would be very useful, but suggest two reasons why it has not been forthcoming:
1. If AOA fails nose down (50% odds), there will be no stick shaker or stall warning or MCAS activation, and it would probably be a non event, written up for maintenance, or reported to the NASA hotline. Conversely if AOA fails nose up on the 'non-MCAS' side (25% odds), there will be stick shaker activation, but it will not be flight critical, and the fault will be repaired. In neither case will the airframe be examined in any detail.
2. In the event of AOA failing nose up and MCAS activating (25% odds), there is an overwhelming fatality rate. There are no known survivors other than the preceding Lion air flight, and unfortunately that airframe was destroyed the very next day, so there is little evidence to strip down and examine (apart from the FDR).
Does this provide some context on the relative scarcity of such occurrences?
As was stated before the AoA vanes are not new equipment and are the same on all the NGs and probably the Classic. There are vast numbers of these flying and as you state they would be just maintenance issues, but all those issues go into analytics and Boeing would have known their failure rate on designing the Max. In knowledge of that failure rate they felt failures were improbable to highly improbable. They also felt that a crew given significant uncommanded nose down trim would immediately trim back nose up and a second uncommanded nose down would result in the crew trimming back nose up then switching off the Stab Trim. It was certainly not expected that a crew would attempt to fly with significant pull force and _not_ trim back. As someone upthread stated trimming is second nature. So add to your probabilities extremely rare failure of AoA vane and Full expectation that 99.9% of PF would trim back to in trim if MCAS did operate incorrectly giving significant uncommanded nose down trim and after 2 or at worst 3 trim back would switch off Stab Trim.

[Rananim]

The MCAS put the aircraft into an almost (or totally) unrecoverable situation at low altitude and no BS about untrained inexperienced pilots is worth a pinch of rocking horse poo.

Sunfish

I cannot concur here.
The Boeing software design error is proven and accepted. Thats not the point here though.This crew did not fly the plane. Single side UAS after takeoff is not difficult.The stick shaker is a huge distraction but they are commercial aircrew acutely aware of the Lionair precedent.They know about MCAS and how it can be triggered in manual flight with flaps UP.Like all good aircrew they will have formulated a plan of action which will help them focus and overcome the danger of the stick shaker and its effect on the human brain's ability to think.
They will brief on what they will do....for every departure!
ISFD and FO ASI are functioning and in agreement.The Captain need only hand control to the FO and instruct him to fly a manual visual pattern at 1500 keeping takeoff flap
setting and land immediately..Right hand on the stick,left hand on the thrust levers,feet guarding the rudders.Fly the plane.
Boeing UAS NNC not applicable here! Just land the plane.

[CodyBlade]

Good info here:

https://theaircurrent.com/aviation-safety/vestigal-design-issue-clouds-737-max-crash-investigations/

[Richard C]

Good info here:

https://theaircurrent.com/aviation-safety/vestigal-design-issue-clouds-737-max-crash-investigations/

Thanks for the link - very disturbing info.

[PaxBritannica]

Humble SLF here, wondering if there's a general rule about speed/autothrottle in a runaway stabiliser situation?

The emergency AD issued by the FAA (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/83ec7f95f3e5bfbd8625833e0070a070/$FILE/2018-23-51_Emergency.pdf)doesn't appear to say anything about speed. Is this just a matter of common sense among pilots, or would the PF have felt that it was sensible to keep the speed high to counter nose-down and hopefully gain altitude? Did he disobey the AD?

[MemberBerry]

Just to confirm, I'm talking about 'Control airplane pitch manually with control column and main electric trim as needed'

This is pretty basic stuff.

Yes, and I agree. But then you could then argue it shouldn't even be included in the memory items, and all the discussion about step 2 is irrelevant here.

It's not exactly the same situation but, I looked again at Mentour's video that demonstrates the runaway stabilizer memory items. They already have the A/P disconnected when the runaway starts, and the thumb switches are not working at all during the runaway. He does try to use the thumb switches to control the trim, but then so did the Ethiopian crew.

https://youtu.be/xixM_cwSLcQ?t=17m18s

This is how it went (some small details omitted):

17:18 - runaway starts
17:28 - Mentour (PF) - "I'm not doing that"
17:40 - F/O (PM) identifies the issue as a runway stabilizer
17:50 - Mentour asks the F/O to perform the runway stabilizer memory items
17:55 - F/O - "control column: hold firmly"
17:57 - Mentour - "holding firmly"
17:59 - F/O - "auto pilot - disengage"
18:01 - Mentour - "autopilot is disengaged"
18:04 - F/O - "auto throttle - disengage"
18:07 - Mentour - "if you can do that for me please"
18:09 - F/O - "disengaged"
18:11 - F/O - "if it continues, I will go with the stab trim cutout switches"
18:13 - Mentour - "ok, let's evaluate this to see if it's moving"
18:20 - F/O - "memory items for the runaway stabilizer complete"
18:21 - Mentour - "yeah, let's evaluate"
18:25 - Mentour - "I have no authority of the trim at the moment"
18:29 - F/O - "roger"
18:32 - Mentour - "I can't control it manually, so it doesn't really work, so if you can continue with the memory items please"
18:37 - F/O - "memory items - stab trim cutout switches to cutout"
18:40 - Mentour - "Continue"
18:41 - F/O moves the switches to the cutout position
18:42 - F/O: "Cutout"

So, between the start of the runaway and using the cutout switches it takes them 83 seconds to perform the runaway stabilizer memory items. With no additional failures and alarms that can distract them and increase their workload. With that in mind, do you think the stabilizer runaway memory items are adequate for dealing with an MCAS failure induced by an AOA sensor failure?

My guess is the Ethiopian crew was aware they could be dealing with MCAS, so they actually skipped some memory items and other procedures to stop MCAS as soon as possible:

05:40:00 - first MCAS AND trim
05:40:12 - pilot ANU trim
05:40:20 - second MCAS AND trim
05:40:27 - the Captain advised the First-Officer to trim up with him
05:40:28 - pilot ANU trim
05:40:35 - the First-Officer called out “stab trim cut-out” two times. Captain agreed and First-Officer confirmed stab trim cut-out.
05:40:41 - third MCAS attempt to apply AND trim, but it doesn't affect trim anymore

They did all that in under 40 seconds.

It's funny. Until the preliminary report was released many people were arguing that the cut-out switches should be used as soon as possible when you are dealing with an MCAS failure. Now people say that you should first bring the aircraft is in perfect trim before doing it. So basically that you should use the cutout switches in a 5 second interval, not too soon, and not too late, or it's pilot error. I disagree. This is not a fighting video game when you have to mash the right sequence of buttons with the right timing to produce a "combo". That's not OK when the lives of hundreds of people are at stake.

[Capn Bloggs]

Just to confirm, I'm talking about 'Control airplane pitch manually with control column and main electric trim as needed'
So what are we doing here, flying by memo? Boeing should have revised the Stabiliser Runway memory procedure!

It knew it had a deathtrap on it's hands, why didn't it insert a line into the memory procedure about trimming to neutral and then switch off the stab trim?

All the background is lovely stuff, but Boeing, you're the experts, give me a couple of lines to hang my hat on and I will not crash the aeroplane. That's what memory items are for, are they not? Certainly, the current Stab Runaway is not appropriate in these cases where the stab had already lost the plot.

[DaveReidUK]

Humble SLF here, wondering if there's a general rule about speed/autothrottle in a runaway stabiliser situation?

The emergency AD issued by the FAA (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/83ec7f95f3e5bfbd8625833e0070a070/$FILE/2018-23-51_Emergency.pdf)doesn't appear to say anything about speed. Is this just a matter of common sense among pilots, or would the PF have felt that it was sensible to keep the speed high to counter nose-down and hopefully gain altitude? Did he disobey the AD?

The 737 FCOM Runaway Stabilizer checklist reproduced in the Preliminary Report (Appendix 3) has, as Item 3: "Disengage (and do not re-engage) the autothrottle".

[Just the fax maam]

The overall trim system now appears to be under scrutiny by several XAA's.

Also, what is more likely in the final dive of both crashes:

Pilots pulling with as much physical strength as they can muster to avert certain death did not think to also apply more than 2 brief blips of ANU trim to help...

Or

For the same reason manual trim is impossible in specific conditions, so is electrically operated ANU trim...

?

Seems to me that once the stab due to MCAS or runaway trim reaches a certain point it is unrecoverable without the old roller coaster manouvre few have been trained on or practiced. And possibly not just the Max.

I hope I am wrong of course, but this story may yet have further twists and turns to come.

[meleagertoo]

Let's not forget that the manual trim may only become immovable at or near max stabiliser travel at normal airspeeds.
It is more than a bit harsh to criticise Boeing when the pilots so mishandle (overspeed) the aircraft it is completely out of all parameters for the trim to work, and neither do they take any recovery action - ie slowing down.
Additionally, Boeing would not expect or anticipate a crew allowing the trim to get so far out of position, the rollercoaster method was a confidence demo to show that even if you did let the trim go to extremes it could never normally achieve in reality it was still recoverable. These pilots did let it get there.
If the pilots don't fly the aeroplane/procedures properly how can Boeing's procedures be expected to cope with that?
There's no certification need or requirement to have manual trim operable at full deflection above VMO - how could there be?

[FlightDetent]

Like a tiny little go-pro, recording a 10 minutes loop onto a titanium-encased SD card with a radio-isotope pinger. Good question why no such thing is already commonplace for at least 15 years. Asking out loud will not win you friends, but the answers are a great research material.

[Capn Bloggs]

It is more than a bit harsh to criticise Boeing when the pilots so mishandle (overspeed) the aircraft it is completely out of all parameters for the trim to work, and neither do they take any recovery action - ie slowing down.
So we're test pilots too now? No mention anywhere by Boeing of keeping the speed down, these guys were probably totally focussed on the MCAS issue, not your bog-standard UAS/80%. Ask yourself: when did you last pull off a handful of thrust at 1000ft above ground, straight after takeoff with the stick shaker going? I would suggest that some pilots don't even touch the thrust levers after takeoff normally, let alone have it in their muscle memory to do it when all hell has just broken loose.

I suspect watching the crew deal with the multitude of alarms and contradictory instruments readings, plus proximity to the ground, on the two Lionair and one ET flight would focus professionals minds a lot more on the human factors issues of these emergencies...
Any professional pilot would already have a very good visual concept of what happened here. Absolutely no need to watch someone dying, thanks.

[meleagertoo]

When all's said and done there was one thing and one thing only missing that on it's own would have totally prevented all this, from LionAir onwards.

I hope I'm not banned for using foul and profane language but the followiing contains adult concepts that some may find deeply offensive and disturbing.

AIRMANSHIP

[Albino]

So what are we doing here, flying by memo? Boeing should have revised the Stabiliser Runway memory procedure

It's in my memory items, right under disconnect autothrottle. Do you fly the 737? Next time you're in the sim put the stab forward to 2 units and leave it there. See how you get on, I doubt you'll consider it to be controlling the aircraft.

He does try to use the thumb switches to control the trim, but then so did the Ethiopian crew.

From the trace they blipped it a couple of times with one slightly larger correction before the cutouts were used. If i've got this wrong then I apologise but as I see it they retained full control of the stabilizer with electric trim at all times (apart from when they cut it out) and it would have overridden any MCAS AND command. After the initial AND command the aircraft is never put back into trim.

[meleagertoo]

So we're test pilots too now? No mention anywhere by Boeing of keeping the speed down, these guys were probably totally focussed on the MCAS issue, not your bog-standard UAS/80%. Ask yourself: when did you last pull off a handful of thrust at 1000ft above ground, straight after takeoff with the stick shaker going?


The last time I pulled a handful of power 1000ft-ish from the ground with stickshaker going was probably the last time I got one in the sim - as I accelerated towards flap limiting speed having already determined on which side the error lay, with correct pilot flying and confidence in my airspeed. How 'bout you?

You must know by now that MCAS didn't (couldn't) start it's tricks until flap was retracted...er...don't you?
Question is, would Test Pilot Bloggs actually retract flap in that situation? Even if you were climbing to 4-5000agl to complete the troubleshooting what would you be doing with the power at that point? Leaving it at climb thrust like these guys? Climbing at 200Kts, Flap 5 at 6000fpm and a pitch angle of 15degrees, with a stickshalker going???? But they were flying level-ish, not climbing!
Does Boeing actually need to tell you that?

See my post #3515 above...

[MemberBerry]

From the trace they blipped it a couple of times with one slightly larger correction before the cutouts were used. If i've got this wrong then I apologise but as I see it they retained full control of the stabilizer with electric trim at all times (apart from when they cut it out) and it would have overridden any MCAS AND command. After the initial AND command the aircraft is never put back into trim.

No, I agree, they didn't fully reverse the MCAS AND trim before using the cutout switches. I was just saying that they did use the switches in the ANU direction, to reverse part of the trim applied by MCAS, not that they fully reversed it.

I can only guess why they didn't fully reverse the AND trim applied by MCAS. Maybe it was the fear of MCAS doing it again, so they hurried to use the cutout switches. Maybe it was the fear of being close to a stall, and didn't want to make any large adjustments in the ANU direction.

Also, the trim adjustment speed available to MCAS is higher than the speed available to the pilots, 0.27 units/s for MCAS vs 0.18 units/s for the thumb switches. So, if MCAS trims for 9 seconds AND, you would then need to trim with the thumb switches for 14 seconds in the ANU direction to fully reverse the 2.5 units of AND trim introduced by MCAS. Anything less than that, and you will lose the fight at some point.

[Derfred]

Best as I can piece together from the report, the successful 11-second (approx) electric ANU trim from 0.4 to 2.3 units took place at 325-330 kts (05:40:28 to 39). Capt control column aft displacement during this time varied from 12 to 5 degrees.

The two “blips” of electric trim (suggested by some as failure of electric trim) from 2.1 to 2.3 units took place at 360-365 kts (05:43:11). Capt control column aft displacement during this time varied from 9 to 6 degrees.

Airspeeds deduced from the narrative based on the F/O’s airspeed (the presumed correct one). VMO for is aircraft is 340 kts. Control column inputs based on the FDR chart.

A question then becomes, is the difference between 325-330 kts and 360-365 kts enough to overwhelm the electric stab trim with these kind of control column displacements?

Obviously the second case is outside of design parameters, and therefore may not even be able to be tested in a simulator (unless the simulator is certified to 365 kts).

On another note: some have suggested that the “blips” would be due to severe G-forces resulting from each blip. I don’t buy it. G-forces are mapped in the FDR plot (vertical acceleration), and they are insignificant - certainly much less than the pilot-induced G-forces of the previous couple of minutes. And let’s get serious for a moment - is a bit of trim-G going to bother you if you’ve had two pilots pulling on the column for dear life for the past few minutes?

I’ve never hand-flown a B737 at 365 kts before, but I have hand-flown one at 320 kts plenty of times - and trimming is not an G-force inducing event at that speed.

[Derfred]

Anything less than that, and you will lose the fight at some point.

That’s not entirely true, as soon as MCAS starts trimming you can stop it with a reverse blip. You don’t need to wait for it to punish you for 9 seconds.

[MemberBerry]

To stop it yes. But your "blip" still needs to be 50% longer than the "blip" from MCAS, to fully reverse it.

For example if you let MCAS run for 2 seconds, your "blip" needs to be 3 seconds long to not just stop MCAS, but fully reverse what it did.

[PEI_3721]

yo gums, F16 Guy,
Slightly off topic, but an an analogy of the 737 situation.
The only F16 experience I have, apart from sitting in the prototype at Edwards, was to fly the T33 simulation with side stick, and fixed centre stick (equally effective).
In that time frame the problem of restricting flight envelopes was being evaluated (F16?); thus with increasing AoA, at some point the nose up control was restricted and commanded nose-down preventing limit excursion. However, a high g turning departure / flick with associated roll-coupling put the aircraft above the AoA limit - now what.
The aerodynamics place the aircraft beyond a limit, the software prevents recover (situation not known).

The converse, analogy with the 737 Max is that the software puts the aircraft beyond the limit, and the aerodynamics / mechanics prevent recovery (situation not known).

[Derfred]

To stop it yes. But your "blip" still needs to be 50% longer than the "blip" from MCAS, to fully reverse it.

For example if you let MCAS run for 2 seconds, your "blip" needs to be 3 seconds long to not just stop MCAS, but fully reverse what it did.

Correct, or you could do 3x 1-second "blips", each 4 seconds apart. Or 6x half-second "blips". Or instead of counting, just trim repeatedly and/or continually until the elevator force is neutral, like a pilot. Which he never did.

He did say one strange thing though: if it is correct in translation, he asked the F/O "to trim up with him". This was after the second MCAS. He had only responded to the first MCAS with a relatively short "blip" (2.1 to 2.4 units). The response to the second MCAS (presumably with the F/O "helping") was around 11 seconds and took it from 0.4 to 2.3 units (if only they'd kept going another 11 seconds).

So why did he need the F/O's help to activate main electric trim? It's a thumb switch. Was the stick-shaker that annoying he couldn't activate the thumb switch? Could this mystery have anything to do with the two fatally short "blips" near the end of the flight?

[Chronus]

Here is an interesting piece on the STM :


"• Boeing 737NG • Improve field reliability of the Horizontal Stabilizer Trim Motor (STM) • Solder joint fatigue of the memory chip • 6355C0001-01 to 6355C0001-02
""Joint investigation into the STM’s field reliability with Boeing, along with lessons learned from 737MAX qualification, have yielded design improvements to the Control PWA.".

The link is at:

file:///C:/Users/Tony/Downloads/Jay%20ONeal_Boeing%20737NG%20Stabilizer%20Trim%20Motor%20_A3 02_FINAL.pdf

[hans brinker]

This constant assumption by aircraft manufacturers that the pilots don't know f*** all about flying and insist on installing complicated systems to act as a safety pilot is crazy, how often do pilots stall airliners?? very very rarely is the answer, and if they were stupid enough to stall the aircraft, recovery is relatively simple, assuming some altitude is available. A message to Boeing and Airbus, please let the pilots fly the aicraft you build and stop confusing them with unnecessary and untimately dangerous technology.


Not that simple. As stated already hundreds of times, MCAS is required because of aerodynamic differences with the older model (bigger nacelle, further forward), making the required pull to increase AOA at high AOA too light (best way I can phrase it). You could blame Boeing for not designing a new aircraft, but based on all their other new designs i am sure it would have more, not less envelope protection.

[hans brinker]

But they stayed in ‘level change’ mode all the time. That means that the autothrottle kept the engines at climb thrust all the time.

Both altitude and speed were uncontrolled.

Agree, I meant they had the intent to level of and reduce speed. Because the never got to ALT hold and Speed mode (or whatever Boeing calls it) they remained at full thrust.

[Organfreak]

Here is an interesting piece on the STM :


"• Boeing 737NG • Improve field reliability of the Horizontal Stabilizer Trim Motor (STM) • Solder joint fatigue of the memory chip • 6355C0001-01 to 6355C0001-02
""Joint investigation into the STM’s field reliability with Boeing, along with lessons learned from 737MAX qualification, have yielded design improvements to the Control PWA.".

The link is at:

file:///C:/Users/Tony/Downloads/Jay%20ONeal_Boeing%20737NG%20Stabilizer%20Trim%20Motor%20_A3 02_FINAL.pdf

Sorry, link is bad. Looks as if it's a local file on your puter.

[Chronus]

Sorry, link is bad. Looks as if it's a local file on your puter.

Apologies for that, it is a pdf file on www.eaton.eu

Here is the slide :
Boeing 737NG • Improve field reliability of the Horizontal Stabilizer Trim Motor (STM) • Solder joint fatigue of the memory chip • 6355C0001-01 to 6355C0001-02 5 © 2018 Eaton. All Rights Reserved.. Background Part history • Eaton has been the provider of the Stabilizer Trim Motor used on the Boeing 737NG since 1996. • 6355B0001-02/-03:1996 - 2003 • 6355C0001-01: 2003 - 2017 • 6355C0001-02: 2017 - Present • 6355D0001-01: 2016 - Present • Unique to the 737MAX and not interchangeable with 6355B/C configurations 6 © 2018 Eaton. All Rights Reserved.. Background • Stabilizer Trim Motor (STM) exceeds Boeing’s reliability requirements. However, in partnership with Boeing and using Eaton’s continuous improvement process and operator feedback, design improvements have been made to further improve field reliability. • Primary failure mode is solder joint fatigue of the non-volatile memory (NVM) chip due to a combination of uncontrolled environmental conditions causing bending, vibration and thermal expansion stresses. • Eaton implemented a shimming procedure that will ensure the control printed wire assembly (PWA) is held flat, so that all component leads, including the NVM, are free from mechanical bending stress. This change is identified on 6355C0001-01 units as Modification 9 (“Mod 9”). • Boeing has performed an in-depth analysis of the Horizontal Stabilizer Trim System Wiring design to include ships wiring, switches and production breaks and splices. The results of the Boeing Study show that operators may reduce the No Fault Found test results for the STM by checking the airplane wiring and switching components prior to removal. 7 © 2018 Eaton. All Rights Reserved.. Solution • Joint investigation into the STM’s field reliability with Boeing, along with lessons learned from 737MAX qualification, have yielded design improvements to the Control PWA. • Modifications to the NVM chip package which is significantly more robust to vibration and thermal expansion. • Control PWA changes include NVM component replacement, component land pattern optimization, component height spacers, copper balancing of the PWB, reduction of hand soldering operations and addressing potential obsolescence concerns. • An upgrade of a 6355C0001-01 to a 6355C0001-02 will require a new Control PWA (the PWA itself can not be upgraded). • Long term lab testing of the 6355C0001-02 shows that the failure mode of solder joint fatigue of the Non-Volatile Memory (

[Organfreak]

THANK YOU!

[bill fly]

Just to confirm, I'm talking about 'Control airplane pitch manually with control column and main electric trim as needed'

This is pretty basic stuff.

Also Memberberry and Derfed,

This illustrates my point that the stab runaway checklist is unsuitable for the false MCAS operation case. Point two in the stab runaway checklist presumed that AP was on and that AP trim was the trouble maker, if runaway stops after disconnecting, so now try thumb trim etc.
You can’t just pick bits out of a drill and say “I’ll use this point now”.
What is needed is a QRH checklist with memory items to cover the specific fault, including possible accompanying distracting indications.
As MCAS logic is in the process of being modified, a checklist which might have covered the two fatal cases may well not be suitable for the new mod.
What these men were faced with was a checklist for a different situation, nevertheless recommended by Boeing - no time to reflect on its merits and no ground study of any other suitable procedure.
We can all sit here and sort out measures at our leisure, which those pilots couldn’t.
A new and case specific drill needs to be made before further ops.

[TryingToLearn]

He did say one strange thing though: if it is correct in translation, he asked the F/O "to trim up with him". This was after the second MCAS. He had only responded to the first MCAS with a relatively short "blip" (2.1 to 2.4 units). The response to the second MCAS (presumably with the F/O "helping") was around 11 seconds and took it from 0.4 to 2.3 units (if only they'd kept going another 11 seconds).

So why did he need the F/O's help to activate main electric trim? It's a thumb switch. Was the stick-shaker that annoying he couldn't activate the thumb switch? Could this mystery have anything to do with the two fatally short "blips" near the end of the flight?

If I turn a thunb switch which should turn a wheel and nothing happens, I release it before I cause further damage. Then I ask another person with another thumb switch if the other one is working... This is the only straight-forward strategy, the last straw...
I already raised the questions if the short blips are short because nothing happened. This woult be in line with the CVR. And maybe the Lion Air PF handed over control because he lost control of the el. trim?

So maybe either:
-> the motor overheatet after x cycles / went into thermal protection
-> Aerodynamic forces blocked the motor
-> The jackscrew got damaged (blocking ANU completely)
Both flights showed such blips before things went wrong completely. Such things will probably never show up in the simulator and you presumably won't try them out on test flights either...

Second mystery: Why were 3 AoA sensors damaged or 'misinterpreted' within 5 months? And why are there so many similarities in both maintainence logs? Is this the second bug they found? Data acquisition?

[silverstrata]

These incidents are simply a continuation of the basic 737 problem - that the design is too old, and would not pass modern certification. So we had...

Single rudder actuators, that had a tendency to turn the aircraft upside down.
Patched.
The same warning horn for config and high altitude, resulting in crews running out of oxy.
Patched.
Speedbrakes that caused elevator vibrations and flight control problems.
Patched.
Wing too close to ground for modern fan engines.
Patched.
Fuel pumps relocated into the center tanks, which overheated and exploded.
Patched (sort of).
Stab-trimmer becomes inoperative with high flight loads.
Forgotten about.
Elevators unable to be separated if jammed.
Forgotten about.
Anti-stall trimmers, which fly the aircraft into the ground.
Awaiting a patch.

But how many band-aids can you stick on a 60 year old design?

Silver

[gums]

Salute!

PEI. And Hans.....

Hans is describing my old VooDoo approach to the infamous “pitchup”. The stick got lighter and if you ignored the wing rock and buffet and then pulled more, then guess what? Duhhhhh. We had a manual limiter when not in AP control stick steering, and it took over 60 pounds to overcome. Then you hit the pusher.

The Viper control laws did not command any control surface opposite pilot input until AoA was above 30 digs or so. Then it removed your pitch and roll authority! It then applied anti-spin rudder. Meanwhile, your stab was fully deflected to get the nose down but could not help - you were in a deep stall. Engage and hold the pitch override switch and rock out of the stall. It was hard to get there, but after the new switch we could get out fairly quickly with 10,000 feet or so below. Maybe sooner if you had practiced, heh heh.

So bottomline, is unlike the MCAS, our FBW did not put in commands except as described above. It limited rates, gee and AoA. No matter how much you yanked and banked. About 35 pounds back stick and 17 pounds for roll.

Later, and we can move to Tech Log

Gums sends...

[MurphyWasRight]

Also Memberberry and Derfed,

This illustrates my point that the stab runaway checklist is unsuitable for the false MCAS operation case. Point two in the stab runaway checklist presumed that AP was on and that AP trim was the trouble maker, if runaway stops after disconnecting, so now try thumb trim etc.
You can’t just pick bits out of a drill and say “I’ll use this point now”.
What is needed is a QRH checklist with memory items to cover the specific fault, including possible accompanying distracting indications.
As MCAS logic is in the process of being modified, a checklist which might have covered the two fatal cases may well not be suitable for the new mod.
What these men were faced with was a checklist for a different situation, nevertheless recommended by Boeing - no time to reflect on its merits and no ground study of any other suitable procedure.
We can all sit here and sort out measures at our leisure, which those pilots couldn’t.
A new and case specific drill needs to be made before further ops.

Precisely.

Reading the emergency AD and revised runaway trim checklist issued after the Lion Air accident it is hard to avoid a conclusion that it was carefully crafted to address the newly revealed MCAS system while preserving the 'party line' that the existing checklist would have worked, hence no blame to Boeing.

Especially for english as a second language crews it would be difficult to 'read between the lawyerse lines' to extract the needed critical information, only some of which was in a 'note' not part of the flow.

Had a new clear and forcefull MCAS misbehave checklist been issued at that time we almost certainly would not be 3500 posts into a discussion of an event that cost 157 lives and billions of dollars.

Plenty of good suggestions here so I will add just one for what should have been in the checklist:

In case of a suspected MCAS issue momentary activation of up then down trim every 3 seconds will effectively disable the MCAS system.
The trim and other issues can be addressed in the normal manner while this sequence is continued.

[spornrad]

...He did say one strange thing though: if it is correct in translation, he asked the F/O "to trim up with him". This was after the second MCAS. He had only responded to the first MCAS with a relatively short "blip" (2.1 to 2.4 units). The response to the second MCAS (presumably with the F/O "helping") was around 11 seconds and took it from 0.4 to 2.3 units (if only they'd kept going another 11 seconds).
So why did he need the F/O's help to activate main electric trim? It's a thumb switch. Was the stick-shaker that annoying he couldn't activate the thumb switch? Could this mystery have anything to do with the two fatally short "blips" near the end of the flight?

Before the MCAS input the PF trims up twice with the thumb switch for appr. 3 s each. This results in appr 1 U uptrim stab movement, twice.
At 5:40:15 after the first MCAS ND he trims again up for appr. 3 s. The stab movement is barely visible now on the chart. Then, unusual:
At 05:40:27, the Captain advised the First-Officer to trim up with him.
Why? Is his switch not working correctly?
The trim up (together or) by the FO is the only long one in the entire FDR recording. It shows again a stab movement at appr 1 U / 3 s. It is followed by STAB TRIM CUTOUT.
Is it possible that the PF had a broken trimswitch?

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/403x522/et302_zoom_12a1b16bf287a639d10f7d3706a38bc53023f128.jpg

[wheelsright]

That’s not entirely true, as soon as MCAS starts trimming you can stop it with a reverse blip. You don’t need to wait for it to punish you for 9 seconds.

How do you know that?

[MurphyWasRight]

I think my first line of defense would be to leave the flaps at 1...or get them there. Completely agree on the instructions after the Lion Air crash.
As I said plenty of ideas on what should be in checklist and order of actions etc. I am sure that Boeing engineers/pilots would be able to provide the best one if given the mandate.

An interesting outcome of the inevitable legal discovery actions will be the internal Boeing discussions leading to the AD and revised checklist. How much pressure to "keep it in type" and similar.

[RickNRoll]

So we're test pilots too now? No mention anywhere by Boeing of keeping the speed down, these guys were probably totally focussed on the MCAS issue, not your bog-standard UAS/80%. Ask yourself: when did you last pull off a handful of thrust at 1000ft above ground, straight after takeoff with the stick shaker going? I would suggest that some pilots don't even touch the thrust levers after takeoff normally, let alone have it in their muscle memory to do it when all hell has just broken loose.


Any professional pilot would already have a very good visual concept of what happened here. Absolutely no need to watch someone dying, thanks.
that's the thing. What testing was done by Boeing to ensure this vital sequence of actions was debugged? The stick shaker was also present on other flights but was ignored by the AD. MCAS runaway was just the endgame of a series of events. That would have taken more time to fully test and document. It would have also been more complex, perhaps necessitating the grounding of the plane so that pilots could have more training. There was no time in that cockpit for the data of debate that are going on in the web.

[deltafox44]

You need to go and read step 2 again. It wasn't completed, at any point after the MCAS AND.

What would disconnecting the autothrottle have achieved? Well you could set thrust to something more sensible and fly the aircraft.

You mean page 2 of the memo that gave specific operating instructions to crew? It even included a note (obvious to most with any common sense!) to put the aircraft in trim, then cut out the stabs.
Not so. Step 2 is "Autopilot (if engaged) disengage". A/P was no longer engaged. So forget Step 2. Even if you don't, it says "Control pitch with column and trim". The pitch has been controled, the trim was back at the limit of green band though a significative column force remained.

Never is said to use electric trim to full trim before cutout, nor any warning that manuel trim might be impossible at higher mistrim/speeds

[deltafox44]

The takeoff ground speed, engine power, and pitch attitude in the climb, would probably all have been higher, to compensate for the lower air density (about 80% of sea level pressure). Not a pilot, but I can't think of any other differences, once they were airborne.
Less oxygen coming to the brain also. May be negligible, especially as they were used to this altitude, not higher than cabin altitude in flight.

[jimjim1]

"as soon as MCAS starts trimming you can stop it with a reverse blip."

How do you know that?

I can't recall exactly but I have seen quite authoritative looking documents on t'interwebby that state it.

You can look for yourself at the LionAir preliminary report and notice the frequent truncated AND automatic trim pulses coincident with manual ANU trim pulses beginning. This was during the period when the captain was maintaining good trim on average for several minutes.

www.flightradar24.com/blog/wp-content/uploads/2018/10/2018-035-PK-LQP-Preliminary-Report.pdf

Edited to add:-
https://theaircurrent.com/aviation-safety/boeing-nearing-737-max-fleet-bulletin-on-aoa-warning-after-lion-air-crash/

Has an image of what appears to be a Boeing document that includes the text "The nose down stabilizer trim movement can be stopped and reversed by the use of the electric stabilizer trim switches ... but may restart ...". See the Orange marked section below.

https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/1084x768/b737_fcomb_3c0c00c3d86287f6874b685b3512b11ec857f01d.png

[deltafox44]

99.9% of PF would trim back to in trim if MCAS did operate incorrectly giving significant uncommanded nose down trim and after 2 or at worst 3 trim back would switch off Stab Trim.
99.9%, really ?

The pilots of the 2 last Lion Air flights did it. The Copilot in Lion Air crash and the Captain in ET302 did not. That's only 50% !

By the way, when speaking that an "average pilot" should be enough to succeed avoiding a crash, it implies that the crash probability is very near 50%, since by definition 49,99% of the pilots are higher than average and 49,99% under average :ooh:

[Airbubba]

Here's an explanation of the EASA position on the observation that the yoke trim switches on the MAX don't work throughout the entire speed envelope (with some highlighted text):

Explanatory Note to TCDS IM.A.120 – Boeing 737 Issue 10

EQUIVALENT SAFETY FINDING:
B-05/MAX: Longitudinal trim at Vmo
APPLICABILITY: Boeing B737-7/-8/-9 REQUIREMENTS: CS 25.161(a), CS 25.161(c)(3), CS 25.1301(a) and CS 25.1309(a) ADVISORY MATERIAL: N/A

STATEMENT OF ISSUE

The aisle stand trim switches can be used to trim the airplane throughout the flight envelope and fully complies with the reference regulation. Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts. In those cases, longitudinal trim is achieved by using the manual stabilizer trim wheel to position the stabilizer. The trim wheel can be used to trim the airplane throughout the entire flight envelope. In addition, the autopilot has the authority to trim the airplane in these conditions. The reference regulation and policy do not specify the method of trim, nor do they state that when multiple pilot trim control paths exist that they must each independently be able to trim the airplane throughout the flight envelope. Boeing did not initially consider this to be a compliance issue because trim could always be achieved, even during the conditions where use of the aisle stand trim switch was required. Subsequent to flight testing, the FAA-TAD expressed concern with compliance to the reference regulation based on an interpretation of the intent behind “trim”. The main issue being that longitudinal trim cannot be achieved throughout the flight envelope using thumb switch trim only.

EASA POSITION

Boeing set the thumb switch limits in order to increase the level of safety for out-of-trim dive characteristics (CS 25.255(a)(1)). The resulting thumb switch limits require an alternative trim method to meet CS 25.161 trim requirements in certain corners of the operational envelope.

The need to use the trim wheel is considered unusual, as it is only required for manual flight in those corners of the envelope.

The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope. Furthermore, the additional crew procedures and training material will clearly explain to pilots the situations where use of the trim wheel may be needed due to lack of trim authority with the wheel mounted switches.

The trim systems on the 737Max provide an appropriate level of safety relative to longitudinal trim capability.

Page 15 of 114

From: https://www.easa.europa.eu/sites/default/files/dfu/IM.A.120%20Boeing737%20TCDS%20APPENDIX%20ISS%2010.pdf

[AerocatS2A]

Not so. Step 2 is "Autopilot (if engaged) disengage". A/P was no longer engaged. So forget Step 2. Even if you don't, it says "Control pitch with column and trim". The pitch has been controled, the trim was back at the limit of green band though a significative column force remained.

Never is said to use electric trim to full trim before cutout, nor any warning that manuel trim might be impossible at higher mistrim/speeds
The AD does in fact say to trim the forces out before using the cutout. https://theaircurrent.com/wp-content/uploads/2018/11/B737-MAX-AD-1107.pdf

[locblue]

Why didn’t Boeing incorporate an MCAS cutoff switch or circuit breaker? Rather than cut out an otherwise perfectly functioning stab trim, just isolate MCAS.

[deltafox44]

Seems to me that once the stab due to MCAS or runaway trim reaches a certain point it is unrecoverable without the old roller coaster manouvre few have been trained on or practiced. And possibly not just the Max.
Please let's all forget the roller coaster theory. At 340 kt releasing aft column pressure would mean negative g's. So if you want to have the time to make the numbers of turns of the trim wheel you need to get trimmed again, you have the choice between an inverted loop or 180° roll before releasing pressure :ooh:

At the end of the flight they got -2g with still both pilots applying full aft force !

[ams6110]

Why didn’t Boeing incorporate an MCAS cutoff switch or circuit breaker? Rather than cut out an otherwise perfectly functioning stab trim, just isolate MCAS.

Because MCAS exists purely in software. There is no separate wiring or mechanism that is specifically "MCAS" it's just the electric stab trim.

[locblue]

Because MCAS exists purely in software. There is no separate wiring or mechanism that is specifically "MCAS" it's just the electric stab trim.

Perhaps therein lies the solution. I wouldn’t trust a “software update” from Boeing to well and truly fix this. They need to redesign MCAS such that it becomes a discrete and isolation-able input. Until, of course, the 737 is redesigned from scratch altogether.

[Flt.Lt Zed]

Why does Boeing not delete MCAS from their new B73 8/9s?. They have thousands flying around successfully without it.

[Airbubba]

"Furthermore, the additional crew procedures and training material will clearly explain to pilots the situations where use of the trim wheel may be needed due to lack of trim authority with the wheel mounted switches."

Some decades ago...

Speaking of decades, what was the date on that document?

The Explanatory Note is an addendum to this EASA Type Certificate document dated December 17, 2018:

https://www.easa.europa.eu/sites/default/files/dfu/EASA%20TCDS%20IM%20A%20120%20-%20rev%2017.pdf

According to a Reuters article the Note dates back to February 2016:

The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said.

https://mobile.reuters.com/article/amp/idUSKCN1RA0DP

[AerocatS2A]

Why does Boeing not delete MCAS from their new B73 8/9s?. They have thousands flying around successfully without it.
They needed it for certification.

[meleagertoo]

Please let's all forget the roller coaster theory. At 340 kt releasing aft column pressure would mean negative g's. So if you want to have the time to make the numbers of turns of the trim wheel you need to get trimmed again, you have the choice between an inverted loop or 180° roll before releasing pressure :ooh:


That's a very authoratative statement from someone who clearly hasn't even taken the trouble to find out what it actually involves!

[meleagertoo]

They needed it for certification.

Might a more comprehensive answer be that they needed it for certification without additional sim conversion training?

Is there any suggestion that an aircraft with those stall characteristics could not be certified at all? Doubtless someone here can advise.

[Loose rivets]

The gist is that it is required. You can't train around it.

By the way.Meleagertoo #3509 There's no certification need or requirement to have manual trim operable at full deflection above VMO - how could there be?
A rather famous ‘Jet Upset’ comes to mind. The possibly supersonic 727 Mind you, it took the undercarriage to save the day, so I suppose the T tail wouldn't have worked anyway.

[Loose rivets]

A ghostly ring in the Aviation VOICE article comparing the sales of Airbus and Boeing. I read the link with an increasing sense of our blindness when we try to look into the future. “Basic market forces are likely to reduce Airbus’s advantage eventually, but it is difficult to imagine a scenario that would cause a shift toward Boeing’s stated goal of a 50/50 balance.” https://aviationvoice.com/airbus-a320-neo-vs-boeing-737-max-2-201602121522/


abdunbar #3492 Super post. https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa-175.html#post10440654

My generation needed to be encouraged to embrace auto flight as it matured. We were spring loaded to dump it and manually fly if we got behind. As the years moved on we started to have new/younger pilots whose only experience was systems, auto flight and flight management computers that could handle all phases of flight except initial takeoff. We were encouraged to use these systems fully to reduce workload.I recall being incensed on behalf of younger pilots about the policy of forbidding crews to hand fly. The main reason given was passenger comfort.


MemberBerry #3497

And having in mind that the current version of MCAS will re-activate in 5 seconds, it should also tell you to use the cutoff switches as soon as possible after you bring the trim to neutral, in under 5 seconds after your last electric trim use.

Can we safely assume that this five seconds starts upon resetting the Stab cut-out switches? The delay might only apply after thumb switch use.
.
.

[FlightDetent]

If any of the insightful contributors could fill my blanks:

How much of trim displacement in units is one spin of the manual wheel on the MAX/NG?

About the yoke elec trim thumb rocker switches
- do they control the actuators/motor directly in analogue, or only send signals to some sort of FCS logical subunit?
- what is the logic for simultaneous inputs L+/-R?

Is there an authoritative answer, whether or not will the MCAS routune re-activation (after the 5 sec denial period) override a live, running trim command from the elec thumb switches?

[Lake1952]

Why didn’t Boeing incorporate an MCAS cutoff switch or circuit breaker? Rather than cut out an otherwise perfectly functioning stab trim, just isolate MCAS.
Because MCAS is not a powered device! It is software!

[FrequentSLF]

A simple question from an engineer, why a designer should put a pilot in such situation, why the designer cannot prevent and design a solid system? And why if he is not able to do so the blame is on the operator? A wrong design is a wrong design, no matter how much you train the operators

[threemiles]

Here's an explanation of the EASA position on the observation that the yoke trim switches on the MAX don't work throughout the entire speed envelope (with some highlighted text):


Explanatory Note to TCDS IM.A.120 – Boeing 737 Issue 10

EQUIVALENT SAFETY FINDING:
B-05/MAX: Longitudinal trim at Vmo
APPLICABILITY: Boeing B737-7/-8/-9 REQUIREMENTS: CS 25.161(a), CS 25.161(c)(3), CS 25.1301(a) and CS 25.1309(a) ADVISORY MATERIAL: N/A

STATEMENT OF ISSUE

The aisle stand trim switches (WHEEL) can be used to trim the airplane throughout the flight envelope and fully complies with the reference regulation.
Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts (EACH FOR ITSELF OR SOME OR ALTOGETHER?).
In those cases, longitudinal trim is achieved by using the manual stabilizer trim wheel to position the stabilizer.
The trim wheel can be used to trim the airplane throughout the entire flight envelope (SAID IN 1ST SENTENCE ALREADY).
In addition, the autopilot has the authority to trim the airplane in these conditions.(OK, BUT WILL IT? WHAT DOES THIS MEAN?)
The reference regulation and policy do not specify the method of trim, nor do they state that when multiple pilot trim control paths exist that they must each independently be able to trim the airplane throughout the flight envelope. (THIS IS WERE THE DINNER WAS BOUGHT. WHEN THERE ARE MULTIPLE METHODS OF TRIM, EACH MAY JUST COVER A BIT OF THE ENVELOPE?? THAT'S RIDICULOUS)
Boeing did not initially consider this to be a compliance issue because trim could always be achieved, even during the conditions AS STATED ABOVE whereuse of the aisle stand trim switch (WHEEL) was is required.
Subsequent to flight testing, the FAA-TAD expressed concern with compliance to the reference regulation based on an interpretation of the intent behind “trim”. The main issue being that longitudinal trim cannot be achieved throughout the flight envelope using thumb switch trim only.

EASA POSITION

Boeing set the thumb switch limits in order to increase the level of safety for out-of-trim dive characteristics (CS 25.255(a)(1)). The resulting thumb switch limits require an alternative trim method to meet CS 25.161 trim requirements in certain corners of the operational envelope.

The need to use the trim wheel is considered unusual, as it is only required for manual flight in those corners of the envelope. (STH BEING "UNUSUAL" IS STRANGE FOR A CERTIFICATION COMMENT)

The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides (THEY MEAN "REQUIRES") a compensating factor for the inability to use the thumb switches throughout the entire flight envelope. Furthermore, the additional crew procedures and training material will SHALL clearly explain to pilots the situations where use of the trim wheel may be needed due to lack of trim authority with the wheel mounted switches (THEY MEAN "THUMB SWITCHES" !!!).

The trim systems on the 737Max provide an appropriate level of safety (SHOULD SAY: COMPLY WITH CS25....) relative to longitudinal trim capability.

Page 15 of 114

EASA aircraft certification document written by an intern.
Never challenged by his/her/its boss to explain what the writing means.
Four terms for the same subject (wheel), totally confusing
Confusing wheel and thumb switch in the most important sentence.
Aviation document quality.

[Lost in Saigon]

Why does Boeing not delete MCAS from their new B73 8/9s?. They have thousands flying around successfully without it.



They needed z for certification.



Might a more comprehensive answer be that they needed it for certification without additional sim conversion training?

Is there any suggestion that an aircraft with those stall characteristics could not be certified at all? Doubtless someone here can advise.

It is not the stall charectoristics. The B737 MAX has pitch up tendencies which don’t meet FAA Static Longitudinal Stability certification standards. To meet the standard, MCAS was needed to reduce the pitch up tendency at high angles of attack.

Addtional sim training won’t exempt you from meeting the certification standard.



Sec. 25.173 Static longitudinal stability.

Under the conditions specified in Sec. 25.175, the characteristics of the elevator control forces (including friction) and the elevator control surface displacement must be as follows:

(a) A pull must be required to obtain and maintain speeds below the specified trim speed, and a push must be required to obtain and maintain speeds above the specified trim speed. In addition, if the elevator control forces are not dependent upon the hinge moments of the elevator control surface, it must also be shown that upward displacement of the elevator trailing edge is required to obtain and maintain speeds below the specified trim speed, and a downward displacement of the elevator trailing edge is required to obtain and maintain speeds above the specified trim speed. This must be shown at any speed that can be obtained except speeds higher than the landing gear or wing flap operating limit speeds or VFC / MFC , whichever is appropriate, or lower than the minimum speed for steady, unstalled flight.

(b) The airspeed must return to within 10 percent of the original trim speed when the control force is slowly released from any speed within the range specified in paragraph (a) of this section.

(c) The stable slope of the stick force versus speed curve may not be less than 0.5 pound for each three knots or exceed a value beyond which control of the airplane is difficult.

[threemiles]

This must be shown at any speed that can be obtained
except
a) speeds higher than the landing gear (VLO) or wing flap (VFE) operating limit speeds or VFC / MFC , whichever is appropriate,
or
b) lower than the minimum speed for steady, unstalled flight.



I read it that this must be shown only for speeds between minimum for steady, unstalled flight and VLO/VFE. MCAS operates when flaps are retracted. The rubber word "appropriate" may be the secret.

[Lost in Saigon]

I read it that this must be shown only for speeds between minimum for steady, unstalled flight and VLO/VFE.

Yes, that is true for condition (a).

I read it that condition (b) and condition (c) must also be met. (c) doesn’t mention a speed range so assume it is for all phases of flight.

[threemiles]

Yes, that is true for condition (a).

I read it that condition (b) and condition (c) must also be met.


Not to be shown for b)
within the range specified in paragraph (a) of this section

Seems to be true for c), though

[Majorbyte]

Gear Up.
Stick Shaker, no problem as the aircraft is in trim, flaps, etc. are all just fine. A-Thl is still in HOLD.
Aviate and navigate.
Call out "AIRPSEED UNRELIABLE MEMORY ITEMS".
Do the MI's which takes 10-15 sec if you are fast or 159 sec if slow and forget them which is usual here.
10 Deg Pitch 80% N1 and simply fly runway heading climbing slowly with slow increasing IAS.
CP calls for the NNC 10.1 and skip Step 7 for now if you wish as that will take too long to open the page. Just keep the pitch and power set above. No terrain, CB's, windshear, TCAS risk, etc.
PM makes the PAN call, reaches and opens the NNC QRH.
Step 9 leads to 10.
Step 10, leads to Step 11 & the FO has Control.
Step 12 would have not worked or maybe just for a while. When the AP drops, manual flying on a beautiful sunny morning. Easy as VMC, two AC power sources, lots of fuel, flaps and slats and gear that will extend normally and crew well rested.
Step 13 switch from Alt 1 to 2.
Step 14 would have taken painfully long as CP's and FO's usually fumble their way thru there. Eventually open NNC page PI-QRH.10.1 & 10.2 and you are finished in maybe 150 to 300 secs.
All the while with F5 and you want to burn fuel anyways.
After Take Off Checklist.
Now all under control, adivse ATC, swing north or south, prepare for an over weight landing, PA to the Seatbelted Cabin Crew and Pax. Even a visual return is no issue as they all grew up flying locally around Addis but FMC still available for the RNAV 07R.
F40, AB3, Max Reverse and expect maybe a brake cooling issue. That is also hard for many to figure out here the Brake Cooling and since over Max Landing Weight you'd need the QRH again for the landing distance,
NNC finished and you will be on the ground in 10 - 20 mins safe after pressing TOGA.
Just like the sim, but the sim sessions at ET are dramatically different and produce this outcome, plus the commercial pressure GET TO NBO ITIS reared its head for sure.
Notes:
They would have kept F5, MCAS remains dormant and you live for another day.
So it comes down to following the standard published Boeing procedures.
That will be exactly how Boeing's massive legal team will argue it for the next many years of litigation.
BUT NO IT WAS A COMPLETE DIVERSION FROM THE SOP, FOM, FCTM, AND QRH and JEP EMERGENCY PROCEDURES.

So in doing what they did, you enter the realm of being a Test Pilot.
In the sim, would have been a Fail for the actual actions taken on March 5th.

Learn from it my Pilot Friends.

so you're blaming both sets of pilots? do you work for Boeing by any chance?

[UnderDuress]

Nope don't work for Boeing but flew the 38M.
Prove me wrong.

[catch21]

Why isn’t there an “MCAS Active” warning or annunciator?