737 Stuck Manual Trim Technique

[meleagertoo]

Inability to operate the manual trim on a 737 is a hot topic just now.

During my 737 type conversion (3-400 series, UK, 1998) we were shown a techniqe for trimming manually even when aerodynamic loads were too large to allow normal movement of the wheel.

A large out-of trim input was provided and an attempt to turn the wheel manually proved it to be immovable. Recovery was for both pilots to pull the column back to give an appreciable pitch up, if only a few degrees, and then relax the pull. The resulting controlled pitch down released enough load on the stab to allow a bit of trim - perhaps less than half a turn initially, to be achieved. The procedure was repeated and with each repetition more and more manual trim was achieveable until a point was reached where normal though very stiff operation became possible.

I seem to recall this was a demonstration that manual trim remained available even in out of trim conditions way beyond those anticipated even in the worst concieveable runaway.

Is this a standard part of 737 conversions or was it an add-on by our very punctilious trainer? I'd be most interested to know how widely this technique is known because once seen, it would never be forgotten. I suspect the Ethiopian pilots hadn't seen this or there would be signs of pulls and bunts on the data, and possibly no acident to discuss either.

737 pilots - over to you....

[Capn Bloggs]

Covered here:
https://www.pprune.org/tech-log/619326-boeing-advice-aerodynamically-relieving-airloads-using-manual-stabilizer-trim.html

I suspect the Ethiopian pilots hadn't seen this or there would be signs of pulls and bunts on the data, and possibly no acident to discuss either.
It appears they couldn't stop the aeroplane flying into the ground, let alone get the nose high enough to do that...

[fdr]

Inability to operate the manual trim on a 737 is a hot topic just now.

During my 737 type conversion (3-400 series, UK, 1998) we were shown a techniqe for trimming manually even when aerodynamic loads were too large to allow normal movement of the wheel.

A large out-of trim input was provided and an attempt to turn the wheel manually proved it to be immovable. Recovery was for both pilots to pull the column back to give an appreciable pitch up, if only a few degrees, and then relax the pull. The resulting controlled pitch down released enough load on the stab to allow a bit of trim - perhaps less than half a turn initially, to be achieved. The procedure was repeated and with each repetition more and more manual trim was achieveable until a point was reached where normal though very stiff operation became possible.

I seem to recall this was a demonstration that manual trim remained available even in out of trim conditions way beyond those anticipated even in the worst concieveable runaway.

Is this a standard part of 737 conversions or was it an add-on by our very punctilious trainer? I'd be most interested to know how widely this technique is known because once seen, it would never be forgotten. I suspect the Ethiopian pilots hadn't seen this or there would be signs of pulls and bunts on the data, and possibly no acident to discuss either.

737 pilots - over to you....

The wording in the FCTM, P 8.17 is rather different to the technique discussed, the nicest thing that can be said is that it is understated and leaves a great deal to the imagination. It may just be that we are all separated by a common language, but being kind, perhaps the FCTM leaves a great deal to the creativity of the TCI/TRI etc. The technique is great sport, not so sure it adds confidence in the strength provided by certification standards. Conceptually, both pilots needed on the controls to deal with a fault that is not impossible to occur seems to be untidy at best. Expecting the crew to undertake aerobatics without having a tail wheel and another set of wings over the top painted in chequers seems to be out of place. There is a silver lining however, that is that the operators should be able to charge more for the disneyland ride that is considered to be appropriate.

If a runaway trim event was about as remote as me winning the lottery, there wouldn't be a problem, it would be hypothetical, and the matter would be just a curious gedankenexperiment, but the recent events suggest it is not, and the 50 years that this has been accepted as a solution may speak loudly to the state of the art. Had Orville suggested to Lt Selfridge that one of the plans of recovery was to follow the wright flyers FCTM in such a manner, the selfless Lt would have probably stayed landside, after all, that was before the time of airline coffee, pretzels and peanuts being served airborne.

FAA Part 142, manual trim use, Yes, manual trim use post stabiliser runaway, No. Yo-yo? Nope. Jack stall from military training only.

[.Scott]

If the trim cannot be brought to within operating range quickly enough, the next option is to roll the plane to invert it - after turning the seat belt signs on. :eek:

[meleagertoo]

Pity, I thought I'd asked a straightforward question, I'll try again.

How many have and have not seen this demonstrated in the sim?

[bzh]

First bring the power back.... 94% power with the nose down will make it impossible to use manual trim, for unreliable airspeed 4deg nose up and 80% power will give you strait and level with flaps out 10deg/75%

[IcePack]

meleagertoo, long time ago but yes i have used that technique. Not exactly taught it at the time but you were supposed to know about "unloading" the airframe. If I remember correctly it was really the only way to get the trim moving manually with the stab run to full down, without rupturing yourself.(737-300)

[sycamore]

What are the flap limiting speeds..? Does the MCAS operate when the flaps are `UP`,or When the flap lever is moved to the `UP` POSITION...?

[BEagle]

..and Boeing expects to carry passengers in these wretched things?

[Derfred]

First bring the power back.... 94% power with the nose down will make it impossible to use manual trim, for unreliable airspeed 4deg nose up and 80% power will give you strait and level with flaps out 10deg/75%

Well, your premise is ok, but your figures are not. Boeing's memory items are 4deg/75% (flaps up) and 10deg/80% (flaps extended).

And that won't give you level flight, it will give you a speed not below minimum, not above maximum, at any weight, and will give you a climb at low level and a descent at high level. In other words, it will give you safe flight without reference to other instruments.

For the OP, no, I've never been trained an unloading technique in the simulator. I've only read about it in my spare time.

[stilton]

We used to practice manual trimming in the
B727 during sim sessions

Required coordination by both pilots and the loads were significant but it was doable


Only once used it in real life after de-icing the stab froze up in cruise but soon freed up
as we descended into warmer air

[Nomad2]

Too much speed can spoil your chances in an unreliable airspeed or 'stab out of position' upset.

But what to do in that first second just after you recognise that you have a problem?

On my last type, a factory pilot told me that the manufacturer designed it in such a way, that if you just put the N1 needles at 12 O'clock, you'll neither go too fast or too slow to get in trouble.

This was on an Embraer, but is there a similar 'rough guide' for the Boeing?

[Capn Bloggs]

But what to do in that first second just after you recognise that you have a problem?

On my last type, a factory pilot told me that the manufacturer designed it in such a way, that if you just put the N1 needles at 12 O'clock, you'll neither go too fast or too slow to get in trouble.

This was on an Embraer, but is there a similar 'rough guide' for the Boeing?
For a UAS, you would do the UAS memory items, which include a pitch attitude and an N1, as pointed out by Derfred in his post above.

[KRH270/12]

Inability to operate the manual trim on a 737 is a hot topic just now.

During my 737 type conversion (3-400 series, UK, 1998) we were shown a techniqe for trimming manually even when aerodynamic loads were too large to allow normal movement of the wheel.

A large out-of trim input was provided and an attempt to turn the wheel manually proved it to be immovable. Recovery was for both pilots to pull the column back to give an appreciable pitch up, if only a few degrees, and then relax the pull. The resulting controlled pitch down released enough load on the stab to allow a bit of trim - perhaps less than half a turn initially, to be achieved. The procedure was repeated and with each repetition more and more manual trim was achieveable until a point was reached where normal though very stiff operation became possible.

I seem to recall this was a demonstration that manual trim remained available even in out of trim conditions way beyond those anticipated even in the worst concieveable runaway.

Is this a standard part of 737 conversions or was it an add-on by our very punctilious trainer? I'd be most interested to know how widely this technique is known because once seen, it would never be forgotten. I suspect the Ethiopian pilots hadn't seen this or there would be signs of pulls and bunts on the data, and possibly no acident to discuss either.

737 pilots - over to you....

What you discribe is Pilot training, thats not done any more...

These days we train operators!

They get airborne with a minor sensor fault and instead of identfying the nature of the failure unverstandig it and flying the aircraft (pitch/power) they operate as usual A/P On, LNAV, flaps up turning HDG bugs talking to ATC etc.

[fdr]

What you discribe is Pilot training, thats not done any more...

These days we train operators!

They get airborne with a minor sensor fault and instead of identfying the nature of the failure unverstandig it and flying the aircraft (pitch/power) they operate as usual A/P On, LNAV, flaps up turning HDG bugs talking to ATC etc.



What is described is also a design that is not compliant with the requirements of Part 25. There is no justification that can be made that an aircraft needs to be handled in such a manner with the failure of a system that is both possible and part of the design requirement to have no adverse effects on failure... Forget about MCAS, how on earth is the procedure in the FCTM reasonable or acceptable. This is not an acro, it is a transport category aircraft.

[Centaurus]

how on earth is the procedure in the FCTM reasonable or acceptable.

If done properly and no doubt Boeing's test pilots did measured tests, then if it saves your life then it's acceptable..Competence as a pilot is preferable of course. But evidence suggests all pilots are not necessarily competent.

[GordonR_Cape]

What you discribe is Pilot training, thats not done any more...

These days we train operators!

They get airborne with a minor sensor fault and instead of identfying the nature of the failure unverstandig it and flying the aircraft (pitch/power) they operate as usual A/P On, LNAV, flaps up turning HDG bugs talking to ATC etc.

AFAIK checklists were introduced to standardise training, and avoid risky seat-of-the-pants flying. Pitch and power is rarely part of standard flying. Unfortunately those checklists don't cover multiple simultaneous warnings, let alone the underlying AOA faults. Ironically, a very short AOA disagree checklist would have helped a lot, but this output was not even included as standard on the flight display. Instead the pilots had to fall back on several half-baked checklists, emergency ADs, and intuitive diagnosis.

[Nomad2]

Thanks Bloggs.

So what N1 do you set on Boeing then?

[KRH270/12]

AFAIK checklists were introduced to standardise training, and avoid risky seat-of-the-pants flying. Pitch and power is rarely part of standard flying. Unfortunately those checklists don't cover multiple simultaneous warnings, let alone the underlying AOA faults. Ironically, a very short AOA disagree checklist would have helped a lot, but this output was not even included as standard on the flight display. Instead the pilots had to fall back on several half-baked checklists, emergency ADs, and intuitive diagnosis.

No its not, i got. about 13k h on the 737 and all the hefty non normals start like this -> A/P OFF, A/T OFF

and then??? Its good old pitch and power, thats not Seat-of-the-pants-flying, its basic flying Skills that are required.

its pitch and power that keeps you airborne...

I agree with you that Boeing messed this one up big time. And i am not blaming the Crew here.

But when most big non normals like engine failures, windshear, runaway stab., TCAS RA, EGPWS warnings, stall recovery require manual flight manual throttle.... you better have well trained pilots on that flight deck rather then minimum trained operators....

[Capn Bloggs]

So what N1 do you set on Boeing then?
:
Well, your premise is ok, but your figures are not. Boeing's memory items are 4deg/75% (flaps up) and 10deg/80% (flaps extended).

In mine, it's 80% in both cases, same deck angle.

[Derfred]

:


In mine, it's 80% in both cases, same deck angle.

Ok, I’m quoting 737. Cheers

[Porto Pete]

Pity, I thought I'd asked a straightforward question, I'll try again.

How many have and have not seen this demonstrated in the sim?

I had 10 years on type at an operator with a reputable training department and this is the first I've heard of this technique.

[OldnGrounded]

. . . has anyone actually used the "roller coaster" or "yo-yo" procedure on a revenue flight?

[astonmartin]

. . . has anyone actually used the "roller coaster" or "yo-yo" procedure on a revenue flight?

I’ve done it during testflights and it is doable. Calling it ‘Yoyo’ would be an exaggeration.

[Roger_Murdock]

Ostrower has a copy of the 1982 FCTM with a description of "roller coaster" technique:

https://theaircurrent.com/wp-content/uploads/2019/04/1981-737-roller-coaster-recovery-1240x1903.jpg

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

[GordonR_Cape]

Ostrower has a copy of the 1982 FCTM with a description of "roller coaster" technique:

https://theaircurrent.com/wp-content/uploads/2019/04/1981-737-roller-coaster-recovery-1240x1903.jpg

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

I find it moderately interesting that the case chosen for evaluation is runaway nose up trim, which is an urgent stall hazard. Presumably nobody in 1982 could visualise the hazards of runaway nose down trim, perhaps due to the limited range of trim travel allowed by the autopilot in the flaps down condition. As the article notes, assumptions made five decades ago, are still propagating through today's 737 flight controls.

[OldnGrounded]

I’ve done it during testflights and it is doable. Calling it ‘Yoyo’ would be an exaggeration.

Thanks. How much air would want below you to have reasonable confidence in recovering in time?

[ProPax]

Recovery was for both pilots to pull the column back to give an appreciable pitch up, if only a few degrees, and then relax the pull. The resulting controlled pitch down released enough load on the stab to allow a bit of trim - perhaps less than half a turn initially, to be achieved. The procedure was repeated and with each repetition more and more manual trim was achieveable until a point was reached where normal though very stiff operation became possible.

How long did it take to reach that point? Doesn't sound like a quick procedure.

[dingy737]

First bring the power back.... 94% power with the nose down will make it impossible to use manual trim, for unreliable airspeed 4deg nose up and 80% power will give you strait and level with flaps out 10deg/75%

4 Set the following gear up pitch attitude and thrust:

Flaps extended . . . . . . . . . . 10° and 80% N1

Flaps up . . . . . . . . . . . . . . . . 4° and 75% N1

[Double Back]

Not active any more but I never forgot the Convair accident due to a reversed trim:
https://www.flightglobal.com/news/articles/ntsb-crashed-convair-580-had-reversed-elevator-trim-cables-326251/
The last weeks It crossed my mind I might have tried to trim even more nose down, in a desperate last attempt to see if the nose would come up...Which in this case would only have sped up the outcome of course...
Remember, those guys were loosing it big time, they were desperate...
Many accidents I have played back in my mind ( a kind of survival procedure for me to deal with terrible accidents), with me making the right decisions and saving the day.
But there are a few cases where I cannot find a realistic better outcome. Like JAL123. I think this MCAS affair is close to that, although technically it was survivable. But You would have to get immediately into the right direction of thinking.
How many times in YOUR career the SIM had to be stopped because Your crew was going down the drain, following a completely wrong lead? I was stopped at least once if I remember correctly....

[FlexibleResponse]

fdr said
What is described is also a design that is not compliant with the requirements of Part 25. There is no justification that can be made that an aircraft needs to be handled in such a manner with the failure of a system that is both possible and part of the design requirement to have no adverse effects on failure... Forget about MCAS, how on earth is the procedure in the FCTM reasonable or acceptable. This is not an acro, it is a transport category aircraft.

Forget about MCAS, how on earth is the procedure in the FCTM reasonable or acceptable.

The design defect of immovable manual trim wheel in the pitch control system under some conditions was obviously acceptable to the FAA 50 years ago to allow certification of the B737 aircraft type.

Grandfather rights on existing certification of the B737 aircraft type has somehow allowed this defect in the flight control system to continue to exist in the modern era.

The high authority automatic MCAS system combined with the low authority manual electric trim system for the pilot to counteract the MCAS, has now shown up this "hidden" design defect in a most dreadful way.

The design defect of the immovable trim at high aerodynamic loads has been festering for 50 years awaiting a system that would reveal it to be a fatal design flaw.

[meleagertoo]

How long did it take to reach that point? Doesn't sound like a quick procedure.
Not too long. It was a while ago but I'd think 4 or 6 repeats from full stab deflection before manual trim became usable without it.
It certainly was neither violent nor extreme manoeuvering, you're only pulling to as much of a normal climb attitude as you can reasonably acheive and then relaxing back to level flight. Pax would find it a bit of an undulationperhaps like flying through wave but to call it "yo-yo' is a big exaggeration. Even roller-coaster greatly overstates it although it illustrates the shape of the thing, if you like.

Next time you're in the sim ask to try it. It's quite a gentle flightpath as you're pulling big forces on the yoke at first.
I'm surprised it disappered from the FCOM though. Mr Boing's gonna regret that decision...

Min height to do this at? 500 feet if you had to - not that you'd choose to do of course. There should be no diving or descent involved, just undulations up from and back to whatever altitude you started from. If you had height to spare ypu might use a bit of descent but it wouldn't be to my taste, I'd not want the nose below the horizon with extreme down-trim simply because of the recovery, and also to avoid airspeed buildup which would surely be obvious to most.

[HalinTexas]

Has anyone read the preliminary report here? They used the electric trim 30 seconds before the crash. MCAS responded again. Airspeed was about 350 KIAS.

So, it would seem to me that if the electric trim could move the wheel, and that it can be stopped and overridden by hand power, that manual trim should have worked. 350KIAS should NOT be too fast for manual trim. Since they followed and summarily rejected the QRH and improvised, then who is at fault, or at least share fault? There was no reason to turn the electric trim switches back on, but since they did, they should have used it! If they had, they could have saved the airplane. I'll give the Lion Air guys a bit of a pass, but not much. They have a horrible reputation in the training department.

But what do I know. Six airlines in four countries on the B737 and I teach on it. Read the reports. Read them with a skeptical eye. They are surprisingly incomplete.

[Capn Bloggs]

Since they followed and summarily rejected the QRH and improvised, then who is at fault, or at least share fault?
The report clearly states, after they turned off the stab trim, "At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough."
Then there were momentary electric trim inputs; I think they realised that they didn't have enough pitch control and decided to try the electric trim again. What would you have done? Just sat there with the switches off because that was the end of the QRH drill and slowly speared in?

There was no reason to turn the electric trim switches back on, but since they did, they should have used it! If they had, they could have saved the airplane.
I think it was a great idea switching them back on. A great pity though that they didn't follow through by trimming against the continued MCAS trim.

[HalinTexas]

I would have recognized a runaway trim. Held the electric trim back until I didn't need so much control force. At the same time I'd call for the "Runaway Stab Trim" QRC/QRH. Used to be a memory item.

Both accidents used the trim to stop the motion, but NOT to reverse the trim. Anyone that hand flies the airplane much knows that you have to trim the hell out of Boeings, and trim some more. I suspect some serious training deficiencies, along with lack of experience.

I'm not buying that they could trim manually. They were doing less than 350KIAS. I suspect they didn't pull the handle out to crank it.

[Capn Bloggs]

Anyone that hand flies the airplane much knows that you have to trim the hell out of Boeings
Therein lies a major part of the problem. Some operators actively discourage hand flying, others virtually prohibit it.

Crews with little general aviation experience just aren't getting enough practice to survive these types of events, and it's not their fault.

[LNAV VNAV -]

Pity, I thought I'd asked a straightforward question, I'll try again.

How many have and have not seen this demonstrated in the sim?

i did my 737NG type rating at Boeing in Seattle in 2004 and I was not shown this technique.

[DaveReidUK]

I'm not buying that they could trim manually. They were doing less than 350KIAS. I suspect they didn't pull the handle out to crank it.

Trim force required isn't just dependent on IAS.

[Cows getting bigger]

Since they followed and summarily rejected the QRH and improvised, then who is at fault, or at least share fault? There was no reason to turn the electric trim switches back on, but since they did, they should have used it! If they had, they could have saved the airplane.

I'll subscribe to your shared responsibility argument. The legal people will split that down into percentages from the following:

1. Aerodynamic development that led to poor static stability at high AOAs.
2. Inadequately deigned software add-on (MCAS) to hide comply with static instability issue.
3. Single point of failure (AOA gauge) in safety critical flight control system.
4. Inadequate training and documentation.
5. Poor Boeing assessment of systematic failures that led to Lion Air crash - initial AD.
6. Failure by Lion Air #1 to articulate and capture problem after first, non-fatal event.
7. Regulatory oversight, lack of?
8. Two slightly dull/average/unlucky crews faced with multiple inputs.

I'll wager that the crew 'percentage' will not be the biggest number.

[GordonR_Cape]

Trim force required isn't just dependent on IAS.

Time to repost this (or similar) article link every time someone also asks about:
- how do manual trim wheels, cables and the jackscrew work
- why the horizontal stabiliser is loaded via opposing elevator aerodynamic forces
- alternative techniques for unloading the HS jackscrew (roller coaster)
- why didn't the pilots do X or Y?
- can the plane fly inverted?
- why was this certified?
See: https://theaircurrent.com/aviation-safety/vestigal-design-issue-clouds-737-max-crash-investigations/

Edit: +1 for Cows getting bigger

[Caygill]

Just out of curiosity, looking at the initial report for the last minutes:
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.

How do you recover without unloading (diving) the aircraft?

[737 Driver]

I'm not buying that they could trim manually. They were doing less than 350KIAS. I suspect they didn't pull the handle out to crank it.

The problem was not just the airspeed but also the extreme out-of-trim state combining to put an excessive load on the jackscrew. Once the aircraft is at or near neutral trim, manually trimming is a pain but doable. However, you absolutely need to keep ahead of it.

Even if it was possible to manually trim in their state, the crew may not have been aware of just how much force it would take. The ops manual does not provide much guidance on this. Since the Captain presumably had all his hands full with the yoke, the FO probably tried the crank handle but either could not turn it or simply did not apply enough force.

[DaveReidUK]

Just out of curiosity, looking at the initial report for the last minutes:
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.

How do you recover without unloading (diving) the aircraft?

Can anyone confirm that electric trim (if enabled) could provide enough force to be able to drive the stab back from full AND at Vmo and any elevator deflection ?

Kind of sounds like it might be a certification requirement, or at least something that Boeing would have flight-tested at some stage in the last 50 years, though probably best not tried at home.

(no criticism intended or implied of the crew's decision to disable stab trim per the checklist)

[GordonR_Cape]

Just out of curiosity, looking at the initial report for the last minutes:
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.

How do you recover without unloading (diving) the aircraft?

This situation has been discussed elsewhere (|including by myself), and the conclusion seems to be that there are very few options left. A gradual reduction in engine thrust, to slowly reduce airspeed below 250kts is a theoretical possibility. However we do not know what effect the reduction in thrust would have on nose down pitch, due to the underslung engines. In any case, this is morbid curiousity, and should hopefully never again be encountered, particularly under these exact circumstances.

Edit: DaveReidUK There seems to be little clear data on the trim forces of a loaded horizontal stabiliser in that flight regime. More research may be needed, if the accident investigation justifies it.

[astonmartin]

Thanks. How much air would want below you to have reasonable confidence in recovering in time?
That depends on elevator authority. And I understand the phenomenon of ‘elevator blowback’ could have played a role....

[Double Back]

Trimming electric plus manual at the same time, wasn't that the reason of the Alaska Airlines crash?
https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261

See how much debating is going on in both threads, see how much we have learned more about the system in the last weeks.
Those poor fellas had to find a solution in just minutes with a situation that was running out of hand big time, causing confusion and CCR breakdown. I wouldn't point a finger yet at the guys up front. Most likely I'll never will.
Let's face it, I admit honestly I wouldn't like to have been in that scenario.
Although I've have never flow 737's but nearly all of the 747 versions, I wonder if I would have made the day with the right decisions.

[sycamore]

What trim changes occur if you pop the speedbrakes..? Nose-up..?
Then select `flaps` to lowest setting,then retrim..?As Ibelieve the MCAS only operates when the flaps are selected `up`..?

[FlightDetent]

gents, anyone able to asnwer these: https://www.pprune.org/showthread.php?p=10441180
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 the re-activation (after the 5 sec denial period) of MCAS software routine could override a live, running trim command from the elec thumb switches? help appreciated.

[GordonR_Cape]

gents, anyone able to asnwer these: https://www.pprune.org/showthread.php?p=10441180
help appreciated.

The only facts that are known (from DaveReidUK) is that one turn of the wheel equals about 0.07 trim units. That is not a misprint, 15 rotations per unit of trim.

Conversely MCAS trims down at 0.27 units per second, or 3.5 rotations of the wheel per second! That is a lot of manual winding, for every 9 second activation.

The rest will have to be officially answered by Boeing engineers.

[Old as Dirt]

I would have recognized a runaway trim. Held the electric trim back until I didn't need so much control force. At the same time I'd call for the "Runaway Stab Trim" QRC/QRH. Used to be a memory item.

Both accidents used the trim to stop the motion, but NOT to reverse the trim. Anyone that hand flies the airplane much knows that you have to trim the hell out of Boeings, and trim some more. I suspect some serious training deficiencies, along with lack of experience.

I'm not buying that they could trim manually. They were doing less than 350KIAS. I suspect they didn't pull the handle out to crank it. The stab in an extreme nose down position with the elevator in a nose up position at 350KIAS would put a significant force on the stab toward the nose down position. Perhaps if the stab and elevator were closer to a trimmed condition trimming at 350 might not be a problem. High speed high deflection - different story.

[fab777]

What is described by the OP was taught to me (But not demonstrated ) when flying a PC6 jumpship, to defeat the classic killer of landing empty with full aft trim and forgetting to set it to half fwd for a full load take-off. Albeit a smaller plane, the PC6 has a full moving stabiliser and is subject to the same problem. This has claimed a number of lives on the dropzones.
Never heard about it on the B737 though.

[capngrog]

[QUOTE=HalinTexas;10441177
There was no reason to turn the electric trim switches back on, but since they did, they should have used it! If they had, they could have saved the airplane.
.[/QUOTE]

In my limited understanding of the B-737 MAX MCAS/trim workings, I believe that once the trim Cut Out switches are opened, the only way to trim the stabilizer is via the manual trim wheels. My friends with Boeing experience say that this is a slow and physically taxing operation. To re-trim the horizontal stabilizer quickly would require closing of the trim Cut Out switches, but, of course, that would allow the MCAS to re-initiate the nose down trim action. The pilots would have had a very small window of opportunity (maybe 5 seconds) in which to close the Cut Out Switches, trim ANU, and open the Cut Out switches before MCAS could resume commanding AND.

Just as a matter of interest, I quote from the Boeing 707 Stratoliner Flight Manual, Revision 11-8-60, entitled "Stabilizer Trim Emergency Operation":

"If the stabilizer electric trim becomes inoperative, the manual trim can be used. Due to the flight loads imposed in an out of trim condition, it may be necessary to release the control column to a low force position and retrim while in an "unloaded" condition. If the airplane is much out of trim , this action will have to be repeated until correct trim is obtained."

The manual also stated that the procedure to "Raise Nose" if the stabilizer was jammed nose down was to deactivate the inboard spoilers and raise the outboard spoilers by operating the speed brake lever.

I don't remember where or how I obtained this manual, but I've had it for 30 years or so.

Cheers,
Grog

[sycamore]

I did ask the question about airbrakes/speedbrakes in #49,but no-one has bothered to answer.
It should be incumbent on pilots to know the effects of secondary controls...usually Lesson #2 in Basic training..
Likewise with power changes,,and flap selection in this case would have stopped the MCAS.....`Aviate` is the first consideration !!!

[FlexibleResponse]

Will Boeing fix the stuck manual trim problem?

Will the FAA de-certify the B737 series aircraft until the stuck manual trim problem is resolved?

Or perhaps, the subject will be quietly buried, to wait for a future opportunity for the problem (inability to manually trim the stabiliser throughout the whole flight envelope) to re-emerge?

[yanrair]

Pity, I thought I'd asked a straightforward question, I'll try again.

How many have and have not seen this demonstrated in the sim?
Was trained this in1969 and have trained it ever since. Also seen it trained up to five years ago. Since then? My problem with current training is the loss of the knowledge base developed over many years as new trainers, themselves new train the newer guys and things get forgotten

[yanrair]

I’ve done it during testflights and it is doable. Calling it ‘Yoyo’ would be an exaggeration.
exactly Aston
its just pull unload-trim while unloaded. And it’s only needed when grossly out of trim which shouldn’t happen

[yanrair]

Just out of curiosity, looking at the initial report for the last minutes:
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.

How do you recover without unloading (diving) the aircraft?
I think the answer is that they didn’t find themselves badly out of trim. It happened over many minutes?? To unload you don’t dive- you release back pressure to zero and trim NU before you get into a dangerous nose down scenario

[yanrair]

In my limited understanding of the B-737 MAX MCAS/trim workings, I believe that once the trim Cut Out switches are opened, the only way to trim the stabilizer is via the manual trim wheels. My friends with Boeing experience say that this is a slow and physically taxing operation. To re-trim the horizontal stabilizer quickly would require closing of the trim Cut Out switches, but, of course, that would allow the MCAS to re-initiate the nose down trim action. The pilots would have had a very small window of opportunity (maybe 5 seconds) in which to close the Cut Out Switches, trim ANU, and open the Cut Out switches before MCAS could resume commanding AND.

Just as a matter of interest, I quote from the Boeing 707 Stratoliner Flight Manual, Revision 11-8-60, entitled "Stabilizer Trim Emergency Operation":

"If the stabilizer electric trim becomes inoperative, the manual trim can be used. Due to the flight loads imposed in an out of trim condition, it may be necessary to release the control column to a low force position and retrim while in an "unloaded" condition. If the airplane is much out of trim , this action will have to be repeated until correct trim is obtained."

The manual also stated that the procedure to "Raise Nose" if the stabilizer was jammed nose down was to deactivate the inboard spoilers and raise the outboard spoilers by operating the speed brake lever.

I don't remember where or how I obtained this manual, but I've had it for 30 years or so.

Cheers,
Grog
that’s exactly what you did on 707. for jammed STAB AND. you opened left spoiler cutoffs =INBOARD spoilers which raised outboard only. Then you split the flaps and lowered only the inboard flaps. Both gave nose up trim.

[yanrair]

Just out of curiosity, looking at the initial report for the last minutes:
1. they find them-self at least 4-5 degree out of trim, cut power to trims trims.
2. the aerodynamic forces and loading is so great that they're unable to operate the trim wheels.
3. they are a 2-3000 feet above ground.

How do you recover without unloading (diving) the aircraft?
I think the answer is that they didn’t find themselves badly out of trim. It happened over many minutes?? To unload you don’t dive- you release back pressure to zero and trim NU before you get into a dangerous nose down scenario

[ecto1]

I did ask the question about airbrakes/speedbrakes in #49,but no-one has bothered to answer.
It should be incumbent on pilots to know the effects of secondary controls...usually Lesson #2 in Basic training..
Likewise with power changes,,and flap selection in this case would have stopped the MCAS.....`Aviate` is the first consideration !!!

Speedbrakes being so close to the CP will not induce a big pitch moment in either direction.

They will kill quite a lot of lift, meaning they will cause the aircraft ROC diminish or even turn the other way all things equal, not what the pilots were looking for.

[ecto1]

I am also quite uncomfortable with the fact that the pilots struggle to attain the pitch up attitude they wanted. Why let stab have more power than elevator by design?

FDR shows unused elevator travel, so it was a force problem.Feel system being 100% artificial (up to the point in which the hydraulic system does not have enough power to lift the elevator), it leaves two possible scenarios:

1) Feel system may overpower a human (I hope not). If it can, it is in this situation (a lot of airspeed, a lot of deflection, boost because of stall (false)). If it does, why not reduce its power a bit?
2) Elevator could not fight the aerodinamic forces (possible). It may be possible to enlarge the balance tab / increase the size of the hydraulic actuators at the expense of elevator speed?

Not saying those are sensible modifications, only trying to understand that specific design decision (which by the way is quite popular among other manufacturers, but far from standard).

[Mac the Knife]

So many stories of potentially dangerous situations arising from autotrim (particularly those that fail to inform the operator that trim is way beyond expected limits). Autotrim is a nice thing to have - saves constant retrimming as fuel is pumped around and SLF move around the aircraft.

Good to have trim-wheels that clack-clack as they rotate, but I'm sure that that repeated noise moves into the background.
Not good when manual operation of trim wheels virtually becomes cosmetic because of aerodynamic resistance away from the middle-ground. And not good when "grab and hold" is virtually guaranteed to take the skin off your palm.

There is so much (often life saving) automation now that it takes a constantly "aircraft-aware" crew to know what and why the aircraft is doing what it is doing. But automation was designed to reduce this need (and often does). Rather too often for my taste, a minor (and perhaps transcendent) anomaly, leads to a cascade of alarms which the operator has to define and prioritise very quickly indeed using memory items and paging through the vast amount of information not instantly available on the various displays.

Nor is this confined to aircraft [although there is no comparison in complexity], modern automated anaesthetic machines can on occasion lead to the same confusion (although it is much easier to turn all the automation off and revert to manual). The same will apply to increasingly automated cars.

Ever since the days when some sensible fellow decided to put wheel-shaped knobs on the "undercarriage down" levers, research has continued on making the wo/man-machine interface more intuitive and giving it more "common-sense" but it is very far from complete. Writing software, as I sometimes have to do, 80% of the time goes into imagining and dealing appropriately with corner cases and black-swans.

It isn't easy and there is always another black-swan hidden unseen and waiting to be triggered - it has to be hypothesised and the appropriate information provided and acted upon (either by the machine or the operator). Automation isn't tough.

Just supposing that on AF447 a sensible girl's voice had said, "Hi guys. I've just lost all my airspeed indicators. Everything else seems to be OK, so I've turned off the autopilot and suggest that you just fly pitch and power until I get the ASIs back."

Do you think Bonin would have firewalled the throttles and hauled back on the side-stick?

Somehow it doubt it

Mac

[safetypee]

Mac,
But ‘sensible girl’ (AF447) did not know, could not know, that all sources of speed were corrupt; that was the underlying problem that the situation was beyond the comparator system’s (allowable) certification specification.

In many ways this is similar with the 737 accidents. The crews were presented with a tactile warning of approach to stall, low speed awareness of the same condition, and several alerts from other systems which at the time might not appeared to be related. What would ‘sensible girl’ say, based on those features, and having to consider individual or combined failures.

And again, with flaps up when the trim started to move - MCAS was operating as designed, and again MCAS continued to move trim according to the ‘allowable’ as-designed system. ‘Sensible girl’ thinks OK, and without means of cross comparing AoA, because with only two installed it is impossible to determine which one is correct (another comparator issue). Thus there was no means by which to enter the system logic to identify design weaknesses and conclude that AoA was the initiating factor, and thus correctly alert the crew.

“Good to have trim-wheels that clack-clack as they rotate, but I'm sure that that repeated noise moves into the background.”
Yes, but why was this feature used in the orrigional design? History, but we forget hard lessons learnt.
Was this feature (and others) robust enough to alert the crew against MCAS, or did the failure condition to which the crew should be alerted overcome all warning systems’ and the crew’s ability to deduce the nature, severity, and consequences of the failure?

Back to the drawing board.

[fdr]

exactly Aston
its just pull unload-trim while unloaded. And it’s only needed when grossly out of trim which shouldn’t happen

Quite, however it doesn't reconcile with being a certified aircraft.

What rule permits

two pilots to be on the controls at the same time?
a necessity to match speed to trim error speed by an abnormal untaught, manoeuvre?
a design that incorporates a trim change that exceeds the certified trim error under 25.255, (10 seconds v 3 seconds)?

What is the minimum altitude for conducting said manoeuvre?

Respectfully, the out of trim standards are inadequate, on brand A or B in the real world, and public safety is hardly being preserved. As an industry, this is pretty untidy.

[yanrair]

Thanks Bloggs.

So what N1 do you set on Boeing then?
220 kts 60% N1 6 deg pitch.

[yanrair]

Just supposing that on AF447 a sensible girl's voice had said, "Hi guys. I've just lost all my airspeed indicators. Everything else seems to be OK, so I've turned off the autopilot and suggest that you just fly pitch and power until I get the ASIs back."

my view too. And the girl knew that pitch power and groundspeed did not equate with stall. 450 kts g/s at the time.
And the pilots should have seen this too. Everything is in the right place except for a lot of distracting warnings.

[yanrair]

Speedbrakes being so close to the CP will not induce a big pitch moment in either direction.

They will kill quite a lot of lift, meaning they will cause the aircraft ROC diminish or even turn the other way all things equal, not what the pilots were looking for.
On the NG Speedbrakes cause small pitch up but not too significant. Can’t see that they are relevant to recent incidents

[nooluv]

Could this type of problem happen with an Airbus A 320 etc? If not why not?

[MurphyWasRight]

Just supposing that on AF447 a sensible girl's voice had said, "Hi guys. I've just lost all my airspeed indicators. Everything else seems to be OK, so I've turned off the autopilot and suggest that you just fly pitch and power until I get the ASIs back."

my view too. And the girl knew that pitch power and groundspeed did not equate with stall. 450 kts g/s at the time.
And the pilots should have seen this too. Everything is in the right place except for a lot of distracting warnings.


An interesting idea would be an 'automation jumpseat pilot/flight engineer' with access to ALL of the sensors (from air speed to gps etc) both 'raw' and corrected, automation state, alarms and pilot butt cheek tension. (Well maybe not the last )

This device would be totally independent, 'read only' with no ability to manipulate controls, it's sole role would be to correlate all the data and offer an opinion when asked (or possibly swear if it detected something really scary?)

Since it would be advisory only it would not need to meet the highest level reliability standards. This would allow for more complex functions that would not be easy to certify to the highest level.

It would not be subject to sensory overload or other human foibles and would be able to incorporate history and trends; AoA was 15, one second later it is 75 strongly suggests that is a root problem.

It could also be provided with a system model to allow testing scenarios to determine the best match for the observed warnings and data.

[Loose rivets]

You know, if I was young again and offered a nice new MAX, I'd feel a lot happier if MCAS was not 'connected' to anything except one of the afore mentioned nice voices. "MCAS, lower the nose . . . lower the nose . . . This is your MCAS speaking." I would then decide how my charge was to be flown.

While in this dream state, I could become the boss of Boeing. 'We're going to have to bite the bullet on this one. What's it going to cost us to hinge the Horizontal Stabilizer at the front?'

The strange thing is, I'm not kidding, though I imagine I wouldn't be the one to make the calls.

[The Mad Russian]

I don’t usually post here, however seems there’s pool of knowledge (some historical) regards the B737 trim system in this thread. The following observation for your interest..

A simulator experiment … Try this in the sim if you get chance, requires some ‘mishandling’ and in this order:

- Conduct GA (Flap 15) with A/T disengaged – set full TOGA N1
- ALT ACQ at say 2500’ AGL manual flight, leave thrust at TOGA N1
- Electric Trim forward for 10-12 seconds continuously (agreed not a normal trim run by any means, quite difficult to force yourself to run electric trim AND for this period)
- Speed continues to accelerates +/- 220-230 KIAS, SFP1 simulation in flap load relief to F10 (from F15)
- Close thrust levers to idle, aircraft will now pitch down, attitude below horizon, KIAS further increases.
- Elevator full aft required to arrest nose drop (which may not be possible)

Now ‘try’ to apply ANU electric trim, stab trim motor will NOT run ANU unless the elevator is moved to a neutral position. With aft elevator input removed the stab trim ‘progressively’ starts to run ANU with control wheel thumb switches held in ANU throughout this maneuver.

This effect occurs in a similar fashion with two different Level D B737-800 FFS devices it’s been tried in, one FFS is a SFP1 simulator the other straight -800.

Would have to assume from that the stab screwjack loading and it’s effect on the trim motor is part of these particular FFS’s aero modeling? Only these Level D devices or other B737-800 FFS too?

[FlightDetent]

In short: (on your FSTDs) When mis-trimmed ND, the electric trim ANU would not engage as long as there is back-pressure on the yoke to keep the A/C from diving?

[The Mad Russian]

Correct (with these FSTDs)...., in the circumstances described, the electric stab trim will not run ANU until aft elevator loading is reduced/or elevator/control column moved towards a neutral position.

[oggers]

...interesting. But the data from ET320 shows that at VMO and mis-trimmed ND, the electric trim worked normally in the ANU direction immediately before they set the switches to cutout.

[The Mad Russian]

I'm no expert on FSTD qualification, I'm sure someone who is much more knowledgable will be along soon.... would the aero loading effect observed in these two 737-800 Level D certified devices be subject to QTG / MQTG (manufacturer data?) or other approved data source for the simulation aero package ?

[meleagertoo]

I'd be surprised if sim modelling goes as far as that.
I think we're at risk of losing sight of the wood for the trees.
The angst and indignation that the trim system behaves in the way it does presupposes that Boeing could and should have anticipated that an aircraft could ever get into such a bizarre part of the flight envelope in the first place. The fact that , afaik, this is the first time in 60 years there's ever been an accident attributed to the previously well known jackstall shows that it is so vanishingly unlikely to occur that its hardly fair to have anticipated it. Indeed, Boeing considered it so unlikely they removed mention of the roller-coaster technique from the manual. That certainly looks like an error now, but no one raised theis as a critical failing before these accidents so no one elase had the awareness of it either.

Any aircraft is likely to become uncontrollable if mishandled as comprehensively as the Mad Russioan's interesting post - and 'm sure we could all come up with endless different gross-mishandling scenarios resulting in an accident. Thais doesn't, in my mind, equate to a design flaw of any great proportions as some are suggesting. Aircraft can and will bite if mishandled. You can't design that out of them, and of course it was a measure to mitigate against this that resulted in MCAS in the first place.

I see considerable parallels between the Air France stall crash and this one. In both cases an errant indication was not isolated or properly dealt with leading pilots to mishandle the aircraft to such an extent that they flew it from a perfectly recoverable situation into one that was extremely difficult to recover from, and didn't realise what they had done. There was none of the indignant howlings we hear today saying that Airbus should be sued into penury and it's directors jailed for manslaughter over the AF accident because they failed to anticipate anyone would point the nose at the moon and trim the aircraft into a deep stall with full power on - but what's the difference?
Neither of these accidents would be credible if postulated before the event, you'd be laughed out of town for suggesring such a thing might happen - so I'm rather sympathetic towards Boeing's stance on the trim matter. Some aspects of MCAS are another thing altogether of course, but again how could Boeing have anticipated anyone would fail to carry out necessary drills, fail to reduce power after levelling out, and fail to trim the aircraft sufficiently? They aren't psychic, no one could possibly have inagined this situation in advance so blaming them so harshly as some are doing seems to me a somewhat OTT application of 20/20 hindsight.

[FlightDetent]

The Mad Russian's profile has the shapes and sounds of the Rostov accident. While there is little if any connection on why and how, the "what" i.e. being unable to trim (fast) enough or overcome with the elevator a speed-dive to ground is identical.

With regards to the observed SIM behaviour: sounds like a training device quirk. If it was correctly replicating a jack-screw siezure due excessive loads, someone would have needed to code that behaviour into the simulation software - meaning it must had been a recognized and documented state in the first place. By all accounts, it is not.

Now, in this thread and elsewhere I read about
- (a) elec trim not able to go all the way to extreme NU/ND (but able to come back from within that range)
- (b) manual trim that does not have enough leverage in the mechanism to move THS under major mis-trim and simultaneous elevator load (the yo-yo recovery technique)

WILD SPECULATION: If either or both of the above two got incorrectly programmed for the SIM, a scenario that The Mad Russian describes could ensue.

[The Mad Russian]

Indeed this scenario described was observed whilst 'further exploring' UPRT 'stall/upset during go-around' training. The 'quirk' or 'effect' was quite a surprise to the 3x TREs present (at least one of which had flown most 737 Variants back to the -200) in the sim on this occasion, to the extent that the scenario was flown several times to ensure what we'd witness was indeed what we'd witnessed as an effect. Later on another FSTD (same FSTD manufacture).

Interesting all same... perhaps indeed a line of code from the 737s ancestry or perhaps indeed not valid data, albeit within the flight envelope (I.E. not the wrong side of the stickshaker or with excessive bank angles etc).

[MurphyWasRight]

Indeed this scenario described was observed whilst 'further exploring' UPRT 'stall/upset during go-around' training. The 'quirk' or 'effect' was quite a surprise to the 3x TREs present (at least one of which had flown most 737 Variants back to the -200) in the sim on this occasion, to the extent that the scenario was flown several times to ensure what we'd witness was indeed what we'd witnessed as an effect. Later on another FSTD (same FSTD manufacture).

Interesting all same... perhaps indeed a line of code from the 737s ancestry or perhaps indeed not valid data, albeit within the flight envelope (I.E. not the wrong side of the stickshaker or with excessive bank angles etc).
Interesting experiment would be run the scenario and see if AND does work, which my understanding is that it should not due to column cutout switches. If it does the SIM has this backwards somewhere. Also to notice is whether electrical trim re-appears all at once or begins to work slowly at some point.

The sim probably does include aeroloads on the trim system, the video of pilots unable to manually trim while 2.5 out of trim suggests that it does. Also appeared to have good modelling of the 'spring' in the long control cables.
How/if these loads affect the (simulated) trim motor is an open question although it certainly could and would not need to be part of a predefined error package/scenario.

[MurphyWasRight]

and didn't realise what they had done.

and didn't realise what they MCAS had done.


Neither of these accidents would be credible if postulated before the event, you'd be laughed out of town for suggesring such a thing might happen - so I'm rather sympathetic towards Boeing's stance on the trim matter. Some aspects of MCAS are another thing altogether of course, but again how could Boeing have anticipated anyone would fail to carry out necessary drills, fail to reduce power after levelling out, and fail to trim the aircraft sufficiently? They aren't psychic, no one could possibly have inagined this situation in advance so blaming them so harshly as some are doing seems to me a somewhat OTT application of 20/20 hindsight.

Agreed, before Lion Air suggesting that a new undocumented feature relying on a single sensor would have a death wish would have indeed been laughable.

Truly tragic is the CYA manner the AD was written, rather than simple and forcefull checklist for MCAS misbehave.

Would be interesting to hear why mention of the 'yo yo' technique was removed along the way.

Additional point:
A true trim runaway (stuck relay/whatever) at high speed could get into this state before the pilots recognized and cut out the trim motors, so hard to see how this is unimaginable. About 5 seconds or so appears to do the trick.

[meleagertoo]

Or a lawyer read it and said, "Hey, get THAT out of there. Nobody is going to certify that in today's environment!"
Total topsy-turvey irrational logic, typical of so much of the irrational criticism here.
You cannot remove the fact that this procedure was once published, that is an established fact. Removal of it from recent manuals cannot change the reality that is already proven. History tells us there never was anything seen wrong with the trim system or it's procedures in the 60 years before this - suddenly finding something there now is far too close to 20/20 far-too-clever hindsight.

[PerPurumTonantes]

Total topsy-turvey irrational logic, typical of so much of the irrational criticism here.
You cannot remove the fact that this procedure was once published, that is an established fact. Removal of it from recent manuals cannot change the reality that is already proven. History tells us there never was anything seen wrong with the trim system or it's procedures in the 60 years before this - suddenly finding something there now is far too close to 20/20 far-too-clever hindsight.
Having dealt with a scenario like this in certification (different industry, still safety related), it's a perfectly reasonable point. A lawyer and a paranoid engineer going through the manuals may have suggested deletion. The fact that it had been published doesn't matter, their point would be "we can't recommend this as a procedure any more"

At the end of the day we don't know why it was removed so it's speculation on both sides.

[The Mad Russian]

[QUOTE=MurphyWasRight;10447583]Interesting experiment would be run the scenario and see if AND does work, which my understanding is that it should not due to column cutout switches. If it does the SIM has this backwards somewhere. Also to notice is whether electrical trim re-appears all at once or begins to work slowly at some point.

Useful discussion of stab screwjack loading here: https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-range.html

Would suggest that the effect we observed was correct for stab in (gross mis trimmed) AND position (stab leading edge UP) and aft elevator applied. We didn't try AND electric trim, just ANU electric to avoid impending terrain impact with our particular scenario.

During the described scenario, the reactivation or 'release' of the stab trim wheels was 'progressive' as the aft elevator back pressure/position from aft stop was released, certainly not a 'switch' like effect.

An aside, both the devices mentioned also have a faults for 'stab trim brake failure', this runs the stab according to aerodynamic loading on the stabiliser. A slow and insidious failure... requires NNC memory item for 'if runaway continues' ... stab trim wheel 'grasp and hold', very easily stopped with the palm of the hand on the opposite trim wheel for this simulated fault. I note this in passing, as not all FFS that I've used have such an expansive fault list.

[GordonR_Cape]

MurphyWasRight

Agreed, before Lion Air suggesting that a new undocumented feature relying on a single sensor would have a death wish would have indeed been laughable.

Truly tragic is the CYA manner the AD was written, rather than simple and forcefull checklist for MCAS misbehave.

Would be interesting to hear why mention of the 'yo yo' technique was removed along the way.

Additional point:
A true trim runaway (stuck relay/whatever) at high speed could get into this state before the pilots recognized and cut out the trim motors, so hard to see how this is unimaginable. About 5 seconds or so appears to do the trick.

To their credit, I would assume that the runaway trim procedure was written considering the entire flight envelope. Statistically this would be more likely to occur at altitude, rather than close to the ground, where the aircraft spends a limited time. Not a great assumption, but in the normal scenario, there would be more time for recovery procedures.

The fact that MCAS triggered shortly after takeoff, made the outcome diabolical, when the other factors came into play. If MCAS triggered at altitude, the outcome would probably be more benign, with time for the yo-yo unloading technique.

Perhaps this lack of foresight led to the blandness of the emergency AD. Prior to ET302, almost nobody would have believed that the same outcome could be triggered by two consecutive AOA sensor failures at the same stage of flight, and disaster still not be prevented by the suggested actions.

[MurphyWasRight]

MurphyWasRight

To their credit, I would assume that the runaway trim procedure was written considering the entire flight envelope. Statistically this would be more likely to occur at altitude, rather than close to the ground, where the aircraft spends a limited time. Not a great assumption, but in the normal scenario, there would be more time for recovery procedures.

The fact that MCAS triggered shortly after takeoff, made the outcome diabolical, when the other factors came into play. If MCAS triggered at altitude, the outcome would probably be more benign, with time for the yo-yo unloading technique.

Perhaps this lack of foresight led to the blandness of the emergency AD. Prior to ET302, almost nobody would have believed that the same outcome could be triggered by two consecutive AOA sensor failures at the same stage of flight, and disaster still not be prevented by the suggested actions.

It can also be argued that checklists and training should consider the worst possible time for an occurrence. How often do you get engine out drill in sim while cruising along?
Takeoff/landing is much more dynamic than cruise so more likely for something to fail so statistics could be misleading.

Sadly the AOA sensor failures were not at same stage of flight, Lion Air had a bad sensor for the entire penultimate flight, which if corrected would have prevented the Lion air accident.
ET had an event at takeoff, either a bird strike or a latent fault literally shaken loose.
Both of course lead to disaster shortly after takeoff when MCAS was unleashed.

Hard to get past the feeling that the 'blandness' (good description btw) was part of an effort to preserve the "no changes no training" company line on the MAX.

[meleagertoo]

"Blandness"

It is surely essential that checklists and ADs are bland, that is part of their nature. It is not appropriate to used nuanced language in these, just bare statements of fact. It is up to pilots to nuance them, where they do it in crewroom discussion or in flight.
The AD following the Lionair accident has been criticised for understating the effects and environment caused by the associated additional warnings, a 'mere' list of contrary indications, stick shaker, apparently unconnected warnings etc understating the confusion and bedlam of the real event.
Guys, we're Professional pilots, it's up to us to use our Professional systems knowlege and imagination to read past Boeing's list of cold facts to picture what the reality is like. It is most certainly not appropriate for Boeing to go injecting emotions or human preceptions/reactions into a checklist.
Surge-Limit-Stall doesn't start with 'If there's a big scary noise from the engine that makes you jump...' does it? Where is the nuanced language in the V1 reject actions? Or a rapid depressurisation? It's just a list of facts. If you're not imaginative enough to read between the lines and visualise and prepare for the BANG! and WHOOOSH! deafening noise and agonising barotrauma that might go with it then stick to reading the daily mail on a train, why would/should Boeing patronise you with emotional language?



To be fair I suspect most of those calling for such explanations aren't Professional pilots. At least, I sure hope so!

[FlexibleResponse]

came across this thread, relevant quote from it below. Obviously no way of knowing if genuine or not, but given what else has been posted on the difficulty of operating the manual trim wheel, it does sound plausible.


Shutdown caused Boeing crash. - Page 4 - International Skeptics Forum (http://www.internationalskeptics.com/forums/showthread.php?t=335236&page=4)

Quote...

"I agree it's a flawed design. And I used to work there. I'm glad I don't now.

Regarding the trim wheels: When the NG was being introduced, I happened to be the Lead Engineer in charge of them and a whole lot of other stuff. There were some issues. The new display system created a pinch point between the dash and the wheel. We had to make the wheel smaller. And the new trim motor resulted in the wheel, which is directly connected to the stabilizer by a long cable, springing back when electric trim was used. It was an undamped mass on the end of a spring. We had to add a damper.
Result: Depending on the flight conditions, the force to manually trim can be extremely high. We set up a test rig and a very fit female pilot could barely move it.
As I said, I'm glad I'm no longer there."

Alchad

https://www.pprune.org/showthread.php?p=10453797

And what is Boeing going to do about the stuck/jammed manual trim problem?

[MurphyWasRight]

"Blandness"

It is surely essential that checklists and ADs are bland, that is part of their nature. It is not appropriate to used nuanced language in these, just bare statements of fact. It is up to pilots to nuance them, where they do it in crewroom discussion or in flight.
The AD following the Lionair accident has been criticised for understating the effects and environment caused by the associated additional warnings, a 'mere' list of contrary indications, stick shaker, apparently unconnected warnings etc understating the confusion and bedlam of the real event.
Guys, we're Professional pilots, it's up to us to use our Professional systems knowlege and imagination to read past Boeing's list of cold facts to picture what the reality is like. It is most certainly not appropriate for Boeing to go injecting emotions or human preceptions/reactions into a checklist.
Surge-Limit-Stall doesn't start with 'If there's a big scary noise from the engine that makes you jump...' does it? Where is the nuanced language in the V1 reject actions? Or a rapid depressurisation? It's just a list of facts. If you're not imaginative enough to read between the lines and visualise and prepare for the BANG! and WHOOOSH! deafening noise and agonising barotrauma that might go with it then stick to reading the daily mail on a train, why would/should Boeing patronise you with emotional language?


To be fair I suspect most of those calling for such explanations aren't Professional pilots. At least, I sure hope so!
My bolding in above quote.

Totally agree that emotional language has no place in a checklist.

However proficiency at reading between the lines might be especially difficult for pilots with English as a second language,certainly hard to test for.

I believe that lack of systems knowledge is a key issue, to train and test the ability to apply it in real situations is a thorny problem.
It is probably up there with lack practice of manual flying skills as real concerns.
.
The 'blandness' comment on the emergency AD had to do with the possible attempt to minimize the MCAS issue to maintain the claim that existing procedures were sufficient.
What was missing was the clear 'list of facts' and actions, with some of the critical items presented as a note at the end.

I am not at all a pilot but have a lot of experience in analysing problems from an outsider viewpoint.

[fgrieu]

On 2019-09-15, AFP quotes Boeing (https://www.afp.com/en/news/15/boeing-acknowledges-flaw-737-max-simulator-software-doc-1gm9761) as stating:
Boeing has made corrections to the 737 MAX simulator software and has provided additional information to device operators to ensure that the simulator experience is representative across different flight conditions

changes will improve the simulation of force loads on the manual trim wheel

Do we have an authoritative source on if the changes make the simulator's wheel harder or softer, by what amount, and what part of the flight envelope are affected?

[RVF750]

I can confirm that Mechatronix NG simulator we have does not have loading to the trim wheels. Very disconcerting when you try the scenario and the F/O can wind in full Nose down on you.

And no, it's not recoverable in that state. Very sobering.

[e1229]

I can confirm that Mechatronix NG simulator we have does not have loading to the trim wheels. Very disconcerting when you try the scenario and the F/O can wind in full Nose down on you.

And no, it's not recoverable in that state. Very sobering.

360+ hours, 207+ flights to test. Ok. I really would like to know how many of those flights included removing one AoA probe at a random time (physically, not software disable), how many were done in the dark during rain, how many were done with some kind of heavy turbulence, how many were done acting like AF447, how many was done going nose down at high speed.

I know, test flights are there to collect parameters that you can analyze, replicate in the sim, and so on.

But given that MCAS was (not) really tested before and nobody even knew it was a new thing, I hope that Boing has gone to the limits to prove that it is fixed and that all those "undertrained, third world, below average, slow procedure followers" will be able to "just keep flying" if MCAS is active again. Or, even worst, it doesn't activate anymore when it was necessary (since I consider it existed to do something important and wasn't created just to keep engineers doing something in the spare time).

[Romeo E.T.]

Pity, I thought I'd asked a straightforward question, I'll try again.

How many have and have not seen this demonstrated in the sim?

Practice this procedure during sim training on the B727-200 conversion, and again during command upgrade training
Also practiced this when transitioning to the B737-200
but this practice was not in the programme when transitioning to the B737-400 and B737-800

[safetypee]

‘Also practiced this when transitioning to the B737-200
but this practice was not in the programme when transitioning to the B737-400 and B737-800.’

Would the procedure have worked in the simulation of the later aircraft, perhaps not #90. If not then why no questions / safety report to Boeing ; who knew, when, and why no FAA intervention; certification or training. What are the effects of increased tail area on this drill.
Would - will the procedure work in later aircraft; i.e. would crew’s in these aircraft have similar difficulties in managing a trim runaway, as did those in the Max accidents when using the runaway drill for MCAS trim problems.

[RobertP]

If done properly and no doubt Boeing's test pilots did measured tests, then if it saves your life then it's acceptable..Competence as a pilot is preferable of course. But evidence suggests all pilots are not necessarily competent.
Flight crew error statistics support your statement, but what is the cure?

[infrequentflyer789]

Flight crew error statistics support your statement, but what is the cure?

If we're looking at statistics, might I suggest the 737-NG as the cure ?

Pretty much the same aircraft as the MAX, same type rating, no extra flight crew training required, about same price, similar size and load capability, etc. etc.

Rate of flight crew error (well proven over two decades) causing non-survivable crash is roughly two orders of magnitude lower than that of the MAX. Flew for a decade without a crew-error crash.

[Fly Aiprt]

If we're looking at statistics, might I suggest the 737-NG as the cure ?

Pretty much the same aircraft as the MAX, same type rating, no extra flight crew training required, about same price, similar size and load capability, etc. etc.

Rate of flight crew error (well proven over two decades) causing non-survivable crash is roughly two orders of magnitude lower than that of the MAX. Flew for a decade without a crew-error crash.

And fatal crash rates even better than the A320/321/319 family ;-)

[Zeffy]

https://www.seattletimes.com/business/boeing-aerospace/faa-will-move-first-to-approve-the-737-max-to-fly-again-possibly-within-weeks/

FAA will move first to approve the Boeing 737 MAX to fly again, possibly within weeks
May 23, 2019 at 4:00 pm Updated May 23, 2019 at 4:35 pm
By Dominic Gates
Seattle Times aerospace reporter

FORT WORTH, TEXAS — During a break from an international gathering of air safety regulators from around the world, the head of the Federal Aviation Administration (FAA) made clear Thursday that his agency will move first to lift the order grounding Boeing’s 737 MAX and that such clearance could come as early as late June.

“When we get to the point where we can lift this order, we will do it alone,” said Acting FAA Administrator Dan Elwell, explaining that because the U.S. certified the original design, it must be first to certify the Boeing software fix for the flight control system that went awry on the fatal Lion Air and Ethiopian Airlines flights.

Safety regulators elsewhere will make their own decisions after looking at the FAA’s data, he said. Some will accept it, while “other countries have already decided they will not only review our work but look at some other things of interest to them.”

Relations between foreign aviation-safety agencies and the FAA have been strained by two MAX crashes in five months, the FAA’s slowness to ground the planes and subsequent questions about the rigor and independence of the agency’s certification process.

“There will be some kind of lag,” he said. “Every country has their own process. They never just blindly accept what we do.”

Ali Bahrami, the FAA’s head of aviation safety, said some countries are seeking more detail on the basis of the assumptions that go into the FAA’s system safety analysis.

Elwell said the FAA must finish its system safety analysis of the problematic flight control system, called MCAS (Maneuvering Characteristics Augmentation System), and conduct a series of flight tests followed by a “robust analysis” of the data the test flights generate.

He resisted citing any timeline for this work, saying that “the safety of the 737 MAX, that’s my only target.”

However, he also said that once Boeing submits its finalized software update, “we generally think our work should take about three to four weeks.”

Boeing is expected to submit its final software fix within days. The manufacturer said last week its update was completed, and it was expected to be submitted by now. So this suggests that if no further delays happen, it’s possible the FAA could give clearance to fly by the end of June.

The MAX operators in the U.S. — American, Southwest and United — would then need some time to install the update on their grounded aircraft and to do mandated training with all their 737 pilots before putting the MAX back in passenger service as early as late August.

Elwell warned that if FAA technical specialists find issues with Boeing’s fixes, that could cause more delay.

Separately, a Technical Advisory Board consisting of FAA and NASA specialists who are not working directly on the project will independently review the FAA’s certification of the MCAS fix and “if they find something they want us to look closer at, we’ll do it,” Elwell said.

Elwell insisted that “the public can trust that the FAA will not let the 737 MAX fly again in the U.S. until it is safe to do so.”

He said his agency is dedicated to making the U.S. “the safest possible airspace in the world” and pointed to the safety record of the past two decades: 90 million flights by U.S. registered airliners, carrying 7 billion passengers, with just a single fatality, after an engine blowout broke a passenger window on a Southwest Airlines jet last fall.

“Aviation is still the safest mode of transportation on the planet,” Elwell said. “Once the 737 MAX is safely flying again, it might take some time, but I think the public will become comfortable.”

In interviews Thursday, Elwell reiterated his view expressed in Congressional hearings that once the accident investigations in Indonesia and Ethiopia are complete, the cause of the two accidents will be revealed as “a chain of events” and that “the procedures the pilots did or didn’t do” as well as the maintenance of the aircraft will have to be scrutinized.

Elwell’s comment about potential maintenance issues is likely a reference to the Lion Air accident. In the two flights of that same jet immediately prior to the crash last October, the sensor that triggered MCAS gave false signals — one sensor was replaced — and caused severe flight control problems, though the plane was still cleared to fly.

However, Elwell said Boeing’s MCAS flight control software is “the issue that links these two horrific accidents.”

“We are going to mitigate that,” he said.

Elwell said after the meeting of regulators from 33 nations ended that the gathering had been “comprehensive and constructive.”

“When we broke, there was a great buzz” among the delegates, said Elwell. “I definitely got the impression that what they had heard was extremely helpful to them.



Dominic Gates: 206-464-2963 or [email protected]; on Twitter: @dominicgates.

[Zeffy]

https://boeing.mediaroom.com/2019-05-23-Boeing-Statement-on-Federal-Aviation-Administration-Global-Regulators-Meeting

Boeing Statement on Federal Aviation Administration Global Regulators Meeting
CHICAGO, May 23, 2019 – We appreciate the FAA's leadership in taking this important step in bringing global regulators together to share information and discuss the safe return to service of the 737 MAX. Our team, our airline customers, and regulators place the highest priority on the safety of the flying public. Once we have addressed the information requests from the FAA, we will be ready to schedule a certification test flight and submit final certification documentation.

Contact
Boeing Communications
312-544-2002
[email protected]

[Longtimer]

If, as it has been said, the force to turn the manual trim wheel (if the MCAS goes amuck) is higher than the crew can overcome, it would seem that the aircraft can not be certified until that problem is solved.

[safetypee]

Ref Boeing 737 Detailed Technical Data (http://www.b737.org.uk/techspecsdetailed.htm)
This indicates that the horizontal stab tail areas have increased in latter variants of the 737, approx 29 up to 33 sq m.
What effect might this have on the ability to move the stab with the manual trim wheel.

Longtimer, not so much a MCAS issue after modification, but still an important problem for tail trim runaway.

The recent Boeing statement (#98) does not have the same ‘ring’ of confidence (early return to service) that previous statements had.

Possibly a reflection on yesterday’s regulatory meetings.
Elwell confirmed that Boeing’s final application for changes to the MAX’s maneuvering characteristics augmentation system (MCAS) has not been received. Once the package is in FAA’s hands, “we will perform our final risk assessments and analysis, taking into account findings of the [Technical Advisory Board] and any information we receive from our international counterparts

[BEagle]

The natural instinct of a pilot facing an uncommanded descent is to apply as much aft control column movement as he/she can manage. But if high control column forces are applied in this situation, is there a risk that this would compromise the ability of applying nose-up trim using the manual trim system? Whereas going against instinct and slightly relaxing control column forces might permit the manual trim system to be used?

I once flew an airliner type which used aileron and spoiler for roll control. If either system jammed, it was possible to unlock the control column in the roll sense, so that whichever system hadn't jammed could still be used - aileron only from the left seat or spoiler only from the right seat. However, if the aircraft was rolling when the control jam was experienced, opposing it with the control column (the natural reaction) could prevent the 'unlock' system being used. It once happened to me during flight; fortunately the procedure was well-known and practised quite often in the simulator. Landing using spoiler only was quite difficult though, as the spoilers only operated when the control column was significantly displaced - giving a sort of 'sloppy neutral' feel.

[ImbracableCrunk]

Has it been explained why Boeing changed the cut-out switches to Pri and B/U? It seems like a lot of our problems would be solved if we could get the electric "manual" trim back without re-enabling MCAS, etc.

[hans brinker]

Has it been explained why Boeing changed the cut-out switches to Pri and B/U? It seems like a lot of our problems would be solved if we could get the electric "manual" trim back without re-enabling MCAS, etc.

In all current abnormal/emergency procedures affecting trim, you switch both off (don't ask me why), so changing them to primary and backup seemed like a good thing (not to me)....

[Loose rivets]

This indicates that the horizontal stab tail areas have increased in latter variants of the 737, approx 29 up to 33 sq m.
What effect might this have on the ability to move the stab with the manual trim wheel.

My question on one of the other threads might fit well here. 47' 1" and 33 sq m is a vast flying surface to screw from the wrong side. It's so instinctively wrong that I assume there must be a good reason it's hinged at the rear.

It's not good enough to cry that it's been flying for so long it must be okay. There's Toronto for a start, and if anything spells how difficult it is to unload the surface, that flight spells it out.

https://www.pprune.org/rumours-news/621879-max-s-return-delayed-faa-reevaluation-737-safety-procedures.html#post10478963

[PEI_3721]

Loose rivets,
‘I assume there must be a good reason it's hinged at the rear.’
A logical view, but the reason probably lost in the 707 records, and a situation where today’s 737 engineers wish it wasn’t so.

Re; tail area increase.
From an aerodynamic view, the increased area was required for the longer, heavier aircraft, more thrust, etc. The forces might be higher, but the overall balance of forces was maintained.
From an engineering view, if the balance was disturbed with significant trim displacement, then the individual higher forces on components could be a problem (hinge moments).

The classic 737 had a problem with trim runaway; it was difficult to trim the horizontal stab with opposing elevator applied. The force imbalance was resolved by unloading the combined ‘stab - elevator’ with a roller coaster manoeuvre, the trim wheel being moved when the elevator was inline with the tail - reduced elevator reaction. This was the basis of the original certification and the forces required to balance the smaller aircraft.

The larger aircraft have increased stab area, the forces are still balanced, but individually could be higher. The need for the trim runaway manoeuvre dipped below the training horizon, possible with a self satisfied ‘it hasn’t happened yet’ (but still the same risk).
But the risk might not be the same.

The trim runaway drill requires pilot recognition and intervention to electrically isolate the trim, and then recover normal trimmed flight using the trim wheel. If the forces involved are higher than the classic, then more nose up pitching moment might not be available due to revised aerodynamic, mechanical, or physical limits, i.e. unable to overcome the higher stab nose-down pitching moment, elevator hydraulics suffer jack stall, or pilot strength. If so then the trim runaway manoeuvre might not be practical.
The crew’s involvement could reduce this problem by holding the trim wheel and with the speed of isolating the trim before reaching the limit condition - not necessarily the stab limit, but the point where the elevator is ineffective. Thus the basis of certification did not change, but the assumptions within the trim runaway drill did. Apparently these were not overtly recognised, but recall the EASA query about the full range of trim in the NG, this also introduced speed; higher speeds higher forces.

The Max has different aerodynamics / thrust, etc, (need for MCAS), so again whilst there was a change in force, but the balance was maintained. This could imply that the trim runaway recovery limit had less margin in crew intervention - time for recognition and action - ineffective elevator for less trim deviation.

The lack of factual evidence from incidents in the NG does not identify any change from the classic runaway drill, but the simulator training tests do (video).
Regrettably, evidence from the Max accidents appears to confirm these difficulties, which could be greater than in the NG (note Max simulator inaccuracies), particularly the effect of speed.

If the suppositions above have value, then the trim runaway drill in the Max requires urgent crew intervention - recognition and isolation, and simultaneous control of speed, and possibly altitude constraint.
Thus the revisited certification question is if the crew participation is realistic for a trim runaway in the Max; a change from the NG.
With AoA input to MCAS clearly it was not, but MCAS will be modified eliminating that specific failure; but the trim runaway condition remains.

1: Yes the human will manage with yet more training, recognise and act quickly. (Currency, memory recall, surprise, experience)

or

2: The accidents identify the realistic expectation of crew intervention for trim runway - time to recognise, time to act, startle, range of piloting experience. (Irrespective of MCAS / AoA distractions)

A judgement; but who judges ?

[krismiler]

https://youtu.be/ZtHBz2-YpWE

[yanrair]

Loose rivets,
‘I assume there must be a good reason it's hinged at the rear.’
A logical view, but the reason probably lost in the 707 records, and a situation where today’s 737 engineers wish it wasn’t so.

Re; tail area increase.
From an aerodynamic view, the increased area was required for the longer, heavier aircraft, more thrust, etc. The forces might be higher, but the overall balance of forces was maintained.
From an engineering view, if the balance was disturbed with significant trim displacement, then the individual higher forces on components could be a problem (hinge moments).

The classic 737 had a problem with trim runaway; it was difficult to trim the horizontal stab with opposing elevator applied. The force imbalance was resolved by unloading the combined ‘stab - elevator’ with a roller coaster manoeuvre, the trim wheel being moved when the elevator was inline with the tail - reduced elevator reaction. This was the basis of the original certification and the forces required to balance the smaller aircraft.

The larger aircraft have increased stab area, the forces are still balanced, but individually could be higher. The need for the trim runaway manoeuvre dipped below the training horizon, possible with a self satisfied ‘it hasn’t happened yet’ (but still the same risk).
But the risk might not be the same.

The trim runaway drill requires pilot recognition and intervention to electrically isolate the trim, and then recover normal trimmed flight using the trim wheel. If the forces involved are higher than the classic, then more nose up pitching moment might not be available due to revised aerodynamic, mechanical, or physical limits, i.e. unable to overcome the higher stab nose-down pitching moment, elevator hydraulics suffer jack stall, or pilot strength. If so then the trim runaway manoeuvre might not be practical.
The crew’s involvement could reduce this problem by holding the trim wheel and with the speed of isolating the trim before reaching the limit condition - not necessarily the stab limit, but the point where the elevator is ineffective. Thus the basis of certification did not change, but the assumptions within the trim runaway drill did. Apparently these were not overtly recognised, but recall the EASA query about the full range of trim in the NG, this also introduced speed; higher speeds higher forces.

The Max has different aerodynamics / thrust, etc, (need for MCAS), so again whilst there was a change in force, but the balance was maintained. This could imply that the trim runaway recovery limit had less margin in crew intervention - time for recognition and action - ineffective elevator for less trim deviation.

The lack of factual evidence from incidents in the NG does not identify any change from the classic runaway drill, but the simulator training tests do (video).
Regrettably, evidence from the Max accidents appears to confirm these difficulties, which could be greater than in the NG (note Max simulator inaccuracies), particularly the effect of speed.

If the suppositions above have value, then the trim runaway drill in the Max requires urgent crew intervention - recognition and isolation, and simultaneous control of speed, and possibly altitude constraint.
Thus the revisited certification question is if the crew participation is realistic for a trim runaway in the Max; a change from the NG.
With AoA input to MCAS clearly it was not, but MCAS will be modified eliminating that specific failure; but the trim runaway condition remains.

1: Yes the human will manage with yet more training, recognise and act quickly. (Currency, memory recall, surprise, experience)

or

2: The accidents identifies a realistic expectation of crew intervention for trim runway - time to recognise, time to act, startle, range of piloting experience. (Irrespective of MCAS / AoA distractions)

A judgement; but who judges ?
Remember the stab on the 707 was much larger than the 737 and the elevator was manually powered- I.e. not powered! 737 is hydraulic. Yet using the correct technique the 707 could be flown safely with runaway stab. Jammed stab. Any which way stab. But we all knew how to fly it and knew that stopping the runaway was paramount.
So the 737with it’s powered elevator and smaller stab, and the fact that you can trim back electrically BEFORE switching off electrical power means it shouldn’t really be that hard. Why the guys on the last two fatal accidents didn’t will be revealed but I’m betting on lack of training leading to lack of basic flying skills, system knowledge and airmanship
cheers
y

[Loose rivets]

Professor Simon mentions 8,000 feet for the simulator crew to action the Roller Coaster recovery, but remind me, just how much height did the ET flight have before it started ingesting rocks? Remember, the jackscrew had gone a long way soon after the autopilot disconnect.

Is much known about that particular vested interest issue? Frankly, I became hostile to that quasi-politition after his first public display.

We've discussed before the ability of a simulator to truly represent such a set of scenarios.

And, the shock factor, along with general psychological factors. And of course, the bazillion other arguments. I'm still with the 'could have done better but huge mitigation' camp.

[yoko1]

Professor Simon mentions 8,000 feet for the simulator crew to action the Roller Coaster recovery, but remind me, just how much height did the ET flight have before it started ingesting rocks?

The more relevant question is how far could the pilot have driven the stab with his yoke switch before they cut out power to the trim motor? Get the stab in the right place first, and no yo-yo maneuver required. The first Lion Air 610 crew and the Captain of the second Lion Air 610 had no problem with opposing the MCAS input with trim. It was only the second Lion Air flight First Officer and the Ethiopian Captain who did not seem to understand that they could still trim with the yoke switch.

[yoko1]

Well, they both "blipped" it, and we still don't know why...was it functional? Was it jammed? Or had they forgotten how to trim, as so many have opined?

If you are referring to the Ethiopian flight, there are plenty of examples from the FDR output that shows a pilot trim input followed by stab movement - there just weren’t enough pilot inputs to counter the MCAS inputs. There are too interesting “blips” at the end. However, by this time the aircraft had exceeded Vmo and there is no guarantee that anything is going to work as it is supposed to once outside the certified envelope.

I think it is much more informative to look at both Lion Air flights. On the first flight, both pilots (there was a transfer of aircraft control) successfully countered the MCAS input with the yoke trim switch until they turned off the stab cutout switches. On the second Lion Air flight (the accident aircraft), the Captain flew for something like 7-8 minutes and maintained aircraft control. At some point he transferred control to the First Officer, and I would suggest that this is the “inflection point” we see in the FDR output where the pilot inputs no longer keep up with the MCAS input. The Captain was likely heads down in the QRH at this point and didn’t realize his First Officer was losing the battle with MCAS.

As I pointed out previously, the evidence strongly indicates that 3 of the 5 aviators who acted as the flying pilot with a malfunctioning MCAS were actually able to keep the plane flying. Unfortunately, two of them were not. Given more time to work the problem, I think it is reasonable to ask whether either of the accident crews would have eventually gotten to the same solution as the first Lion Air crew.

[FlightDetent]

I asked before: If the crew on MAX is holding the yoke thumb rocker for trim, and the MCAS comes for the second push after the cooling off period, will it override the pilot's elec command? And we do not know.

Boeing tells us while MCAS is active the thumb switch will kill it, and I trust them. The question above is about a priority rule in a different scenario, another mode. - and we do not know, only assume.

The connection here is that we see a blip of ELEC TRIM switch on the traces, but we really have no way of knowing what was the commanded input of the crew on the rockers. Or do we? Having read those statements about AoA disagree not plugged in by mistake, and underperforming pilots being the only problem, I have an axe to grind now.

Come on, you self-certified the ND inputs to 1x 0,6 units and then went to build it with a recurring open loop of 2,5 units?! Thus the possibility of crew's inputs being voted out by the internal logic needs to be investigated. Given what we learned, is it really a lower probability of that logic being FUBAR, than a young, proud enthusiastic captain who flies a MAX 3 weeks after a deadly crash with the solution splashed all over the news and the internet not pressing the rocker switch??

[FlightDetent]

For the record, I am on 737 driver's team with respect to the notion that our responsibility is to make sure our side of the street gets cleaned immaculately.

Yet for all we know, the Ethiopean captain may have been here with us in the LionAir thread, even contributing. Until the full truth comes out unpolished, their souls won't rest in peace in fear of such grief and tragedy recurring.

[Loose rivets]

The more relevant question is how far could the pilot have driven the stab with his yoke switch before they . . .

Yes, but it's not the question I asked. The graph of the series of thumb switch input blips - plural - is one of the main puzzles, that and leaving the power so high, but for the moment, the height above terrain re Professor Simon's Youtube statement is, or was, the issue.

[boofhead]

80% of accidents are due to pilot error. Always have been and, apparently, always will be. A mechanical defect might be the initial cause, but in most cases a competent pilot can still safely fly the airplane to a landing. Runaway trim is not limited to the 737 it can happen on any aircraft with electric trim and there are procedures written to correct this fault that any pilot who deserves to be appointed as PIC should know and be able to implement. With the degradation in pilot skills we see happening in every country now, due to the shortage of trained pilots, we should expect more of these types of accidents.
Blaming the aircraft does not help. The ability of a manufacturer to make changes to the design is restricted due to tort pressure/regulation inertia and unlikely to happen, even in this case. If a design is changed there will be multiple court cases saying "See? We told you the design was bad!"
The days when we could expect a normal crew to do a normal job are almost gone. The newbies are not taught as well, are not as experienced when taking the left seat and apparently are guilty of not knowing what they do not know so will continue to fall behind in competence, leading to an increase in pilot error accidents.
It is a different world we are entering. Get used to it.

[safetypee]

boofhead,
You might wish to read the links below and consider alternative views of error,
‘… that ‘human error’ should not be used to explain adverse outcomes.
Instead we should try to understand why the same behaviour usually makes things go right and occasionally makes things go wrong.’

https://static1.squarespace.com/static/53b78765e4b0949940758017/t/5718100f27d4bde89977d93f/1461194775995/Besnard-Hollnagel-2012--Myths-industrial-safety-Tech-Report.pdf

http://www.iploca.com/platform/content/element/24312/ErikHollnagel-SafetyMyths.pdf

[yoko1]

I asked before: If the crew on MAX is holding the yoke thumb rocker for trim, and the MCAS comes for the second push after the cooling off period, will it override the pilot's elec command? And we do not know.

Boeing tells us while MCAS is active the thumb switch will kill it, and I trust them. The question above is about a priority rule in a different scenario, another mode. - and we do not know, only assume.

The connection here is that we see a blip of ELEC TRIM switch on the traces, but we really have no way of knowing what was the commanded input of the crew on the rockers. Or do we?



We have at our disposal three separate FDR outputs (2 Lion Air, 1 Ethiopian). In each and every one of these outputs, automatic trim inputs (STS, MCAS) and pilot trim inputs are shown on separate traces. On yet another trace, stab position is shown. This is how we can tell that 1) the pilot trim was working, and 2) that this input stopped and countered MCAS every single time it was used. So yes, we actually do know.

As far as whether the pilot trim was taken directly from the rocker switch on the yoke or somewhere else, I don't know, but I submit that it does not matter. The only way for pilots to input trim through the electric stab motor is through the yoke rocker switch. I know some other aircraft have different setups for this, but not the 737.

Again, what is clear from these outputs is that at least 3 of the 5 pilots who actively controlled the aircraft during a MCAS malfunction were able to hold their own against these unwanted stab inputs. Two did not resulting in subsequent loss of control.

The issue as to why two of these pilots (particularly the Ethiopian Captain) lacked the basic flying skills the other three possessed should certainly be a key area of investigation.

[FlightDetent]

Thanks for clearing that for me. Those FDR traces, what is their data pick up sensor? I thing the yoke switch itself would be overkill, but if it is only a subroutine in the code ....

[boofhead]

boofhead,
You might wish to read the links below and consider alternative views of error,
‘… that ‘human error’ should not be used to explain adverse outcomes.
Instead we should try to understand why the same behaviour usually makes things go right and occasionally makes things go wrong.’

https://static1.squarespace.com/static/53b78765e4b0949940758017/t/5718100f27d4bde89977d93f/1461194775995/Besnard-Hollnagel-2012--Myths-industrial-safety-Tech-Report.pdf

http://www.iploca.com/platform/content/element/24312/ErikHollnagel-SafetyMyths.pdf


So it is not relevant why they failed to follow the correct procedures? It is not reasonable to expect a person occupying the left seat of an airliner with hundreds of people in the back relying on him to know what to do for a situation that is included in the emergency procedures checklist and that he has been trained on, to do it correctly?

[PEI_3721]

yanrair, # 107
You appear to have overlooked the main point; perhaps the explanation of the difference between balance and absolute force lacked clarity (# 105 https://www.pprune.org/10479475-post105.html).

All aircraft are in balance, irrespective of size or power controls (a simplistic analogous description of a beam balance *). If a system is disturbed or breaks, the ‘twang’ of the more heavily loaded (force not weight) tends to be more difficult to restore.

You similarly overlook the argument that as the aircraft variants have developed, the time available to recognise and act with trim runaway may have reduced. If so, there are situations where it is unreasonable to expect the crew to achieve the performance required for the severity of outcome. The safety margin is in knowing how and when the situation is sufficiently understood to act.

Aviation should not bet on anything, nor shrink behind terms such as basic skill, knowledge, or airmanship without explanation of what these entail and the context in which they are being used. The misuse of these or the assumptions in them - that every pilot will have the same understanding and ability to act, may well be at the root of the Boeing trim problem.

* https://dictionary.cambridge.org/dictionary/english/beam-balance NB aerodynamic notes.

P.S. instead of quoting lengthy posts in full, select the relevant section, or link the post as a reference under its # designation. How to do that: - knowledge, basic skill.

[yanrair]

. 80% of accidents are due to pilot error. Always have been and, apparently, always will be. A mechanical defect might be the initial cause, but in most cases a competent pilot can still safely fly the airplane to a landing. Runaway trim is not limited to the 737 it can happen on any aircraft with electric trim and there are procedures written to correct this fault that any pilot who deserves to be appointed as PIC should know and be able to implement. With the degradation in pilot skills we see happening in every country now, due to the shortage of trained pilots, we should expect more of these types of accidents.
Blaming the aircraft does not help. The ability of a manufacturer to make changes to the design is restricted due to tort pressure/regulation inertia and unlikely to happen, even in this case. If a design is changed there will be multiple court cases saying "See? We told you the design was bad!"
The days when we could expect a normal crew to do a normal job are almost gone. The newbies are not taught as well, are not as experienced when taking the left seat and apparently are guilty of not knowing what they do not know so will continue to fall behind in competence, leading to an increase in pilot error accidents.
It is a different world we are entering. Get used to it.
We can’t and mustn’t get used to more crashes
Train pilots properly. Two possible outcomes from LION AND ET final reports>>>
1 The MCAS inputs + airspeed issues were totally manageable (even if bad design) with well trained pilots. So cause of crash is poor pilots / training issues, with MCAS a contributor MCAS now fixed. Leaves only world wide pilot training issue - nightmare!
2 MCAS + UAS STICK SHAKERS ETC beyond any normal regular line pilot even from major word class airlines. MCAS Is now fixed. Won’t happen again..sigh of relief. Carry on.
I believe 1. to be the true story.
But.......who will write the reports? National authorities of the affected airlines.
Y

[phylosocopter]

afaik, this is the first time in 60 years there's ever been an accident attributed to the previously well known jackstall shows.

does that not make you wonder just a tiny bit ?
is it not possible that had any previous accident been attributed to jackstall neither of these accidents would have happened?

[yoko1]

Or...

3 The MCAS inputs were barely manageable...six out of seven pilots exposed to an MCAS failure did not know what to do, and four of the seven are now dead. The problem was childsplay, however, for yanrair, 737 Driver, boofhead, and a few others... from their armchairs. Boeing built the airplane, Boeing came up with the training, Boeing concealed the existence and behavior of MCAS, and now Boeing SAYS it is fixed, even though there was nothing wrong with it in the first place.

I don't think anyone here is saying MCAS wasn't the problem and doesn't need to be fixed. However, as we all know aircraft accidents almost always have multiple causes so it is not a matter of it being an either/or fix. There has been a consistent trend over the past decade or so implicating crew skills and/or knowledge in commercial airline accidents. The skills a crew brings to a particular flight will be a direct result of their training, experience, and environment. Some of these are under the control of the pilots in question, but much of it depends on the training and corporate cultures of their employers. By laying all/most of the fault for these accidents at the feet of Boeing is, in effect, giving a pass to all the airlines out there who want to keep their pilot hiring and training costs to an absolute minimum. I seriously doubt MCAS will ever be the cause of another commercial airline hull loss, but I willing to bet that inadequately trained flight crews will be.

[JLWSanDiego]

Well put Yoko1

[Fly Aiprt]

We have at our disposal three separate FDR outputs (2 Lion Air, 1 Ethiopian). In each and every one of these outputs, automatic trim inputs (STS, MCAS) and pilot trim inputs are shown on separate traces. On yet another trace, stab position is shown. This is how we can tell that 1) the pilot trim was working, and 2) that this input stopped and countered MCAS every single time it was used. So yes, we actually do know.

Again, what is clear from these outputs is that at least 3 of the 5 pilots who actively controlled the aircraft during a MCAS malfunction were able to hold their own against these unwanted stab inputs. Two did not resulting in subsequent loss of control.

The issue as to why two of these pilots (particularly the Ethiopian Captain) lacked the basic flying skills the other three possessed should certainly be a key area of investigation.

It seems some people here are a bit jumping to conclusions.
Are we so sure that "we actually do know" ?
What makes you believe that they did lose control of the aircraft just for "lack of basic flying skills" ?
Of course you might be privy to facts that we don't know yet, but are we so sure that pilots with "basic flying skills" would have automatically fared better ?
I've seen so many qualified (and sometimes overconfident) pilots lose a big part of their flying skills when suddenly confronted with situation they are not trained for, that I'm getting wary of unsupported declarations.
What is unanswered to this date, is how one of those pilots with those "basic flying skills" would have clearly told the MCAS acting up from just the normal STS operation. How long would it take before the manual trim wheel becomes unmovable ?
I you do actually know, please feel free to share your information with us.
If not, well we're just in the armchair speculation realm...

[FlightDetent]

The MCAS kicks in, the nose gets heavier. You pull, and trim a bit. The MCAS kicks in again, the nose gets quite heavy, you pull and trim - more, for zero forces - to negate both of the MCAS inputs. If for nothing just to relieve the muscle tension.

Is it the shared view here, that neither of the doomed crew did the above? That they all instead of a good thorough spin just made a couple of "blips" and watched the A/C in VMC hit the ground? While pulling with possibly all four hands on the yokes, fighting the 4x increased elev feel computer and still neither of them touched the rocker switches to relieve that physical pressure, save for those blips?

[fdr]

"It must be possible to make a smooth transition from one flight condition to any other flight condition without exceptional piloting skill, alertness, or strength, and without danger of exceeding the airplane (https://www.law.cornell.edu/cfr/text/14/25.143) limit-load factor under any probable operating conditions"

"Approved operating procedures or conventional operating practices must be followed when demonstrating compliance with the control force limitations for short term application that are prescribed"

"When demonstrating compliance with the control force limitations for long term application that are prescribed in paragraph (d) (https://www.law.cornell.edu/cfr/text/14/25.143#d) of this section, the airplane (https://www.law.cornell.edu/cfr/text/14/25.143) must be in trim, or as near to being in trim as practical"

"must meet the trim requirements of this section after being trimmed, and without further pressure upon, or movement of, either the primary controls or their corresponding trim controls by the pilot or the automatic pilot"

"In the out-of-trim condition specified in paragraph (a) (https://www.law.cornell.edu/cfr/text/14/25.255#a) of this section, it must be possible from an overspeed condition at VDF/MDF to produce at least 1.5 g for recovery by applying not more than 125 pounds of longitudinal control force using either the primary longitudinal control alone or the primary longitudinal control and the longitudinal trim system. If the longitudinal trim is used to assist in producing the required load factor (https://www.law.cornell.edu/cfr/text/14/25.255), it must be shown at VDF/MDF that the longitudinal trim can be actuated in the airplane (https://www.law.cornell.edu/cfr/text/14/25.255) nose-up direction with the primary surface loaded to correspond to the least of the following airplane (https://www.law.cornell.edu/cfr/text/14/25.255) nose-up control forces:

(1) The maximum control forces expected in service as specified in §§ 25.301 (https://www.law.cornell.edu/cfr/text/14/25.301) and 25.397.

(2) The control force required to produce 1.5 g."


Other than the fact that the plane doesn't appear to meet these requirements, then blame the pilots at your gratuitous leisure, but know that under the conditions that the crew had, it is unreasonable to blame the pilots for the deficiencies that are evident in the certification standard, the application of the deficient certification standards, and the resultant unfortunate design choices, and finally, the reticence to train the flight crew on a known area of problematic compliance, the reason that MCAS was incorporated in the first place.

The crew are the result of the system that we have all collective responsibility for, the regulator, manufacturer, airline, TRTO's, and passengers. It is an example of the inherent resonance of the system, no particular failure was necessary by overt action, it was inherent in the assumptions of all users as to what the real world was doing, vs reality.

If you need to blame pilots for being the result of the problem, than know that it doesn't result in any increase in system safety as a consequence.

An old Persian saying:

"Arrogance is the capital stock of misfortune",
Pand-Namah Tasnif Saih Sa'di Sirazi, A Compendium of Ethics, translated from the Persian of Sheikh Sady of Shiraz, (1788)

The NTSB had the common courtesy of incorporating the human in the loop for Sully, yet now for ET and Lion it is apparent that it is only reasonable for a certain group of pilots to be considered to be human factors in the loop. That is ethically unjust and shows the inherent bias that exists in the observers and those that pass judgement from the safety of their laz-e-boys.

[boofhead]

I have had this problem (runaway trim) and it was difficult to fly the airplane but I am still here so it was not impossible. I did not give up and flew the airplane to the ground with full nose down trim and because of a broken trim cable, no way to reverse the problem. I also flew the 737 for thousands of hours (although never had the trim runaway on that aircraft). I am not an "armchair" pilot and I do know how to fly and how to perform an emergency checklist. I am appalled at the lack of professionalism shown by the pilots in the two 737Max aircraft and even more appalled at the way so many on this thread are preferring to blame Boeing rather than the real cause of the tragedies because of political correctness. If they get their way they would put Boeing out of business and who would benefit then?

No aircraft is immune from failures of some type, and it is the pilot's job to fly it nevertheless and to keep the people who are placing their trust in him/her safe by at the least maintaining an average level of skill and knowledge. Which is all it takes. You don't have to be a super hero.

Fix the real problem. The human element. Take it as a warning of what will happen if we continue to dumb down (to the lowest common denominator as has been suggested we should be doing). Maybe we should be replacing the pilots with computers. They could not do any worse.

[boofhead]

"It must be possible to make a smooth transition from one flight condition to any other flight condition without exceptional piloting skill, alertness, or strength, and without danger of exceeding the airplane (https://www.law.cornell.edu/cfr/text/14/25.143) limit-load factor under any probable operating conditions"

"Approved operating procedures or conventional operating practices must be followed when demonstrating compliance with the control force limitations for short term application that are prescribed"

"When demonstrating compliance with the control force limitations for long term application that are prescribed in paragraph (d) (https://www.law.cornell.edu/cfr/text/14/25.143#d) of this section, the airplane (https://www.law.cornell.edu/cfr/text/14/25.143) must be in trim, or as near to being in trim as practical"

"must meet the trim requirements of this section after being trimmed, and without further pressure upon, or movement of, either the primary controls or their corresponding trim controls by the pilot or the automatic pilot"

"In the out-of-trim condition specified in paragraph (a) (https://www.law.cornell.edu/cfr/text/14/25.255#a) of this section, it must be possible from an overspeed condition at VDF/MDF to produce at least 1.5 g for recovery by applying not more than 125 pounds of longitudinal control force using either the primary longitudinal control alone or the primary longitudinal control and the longitudinal trim system. If the longitudinal trim is used to assist in producing the required load factor (https://www.law.cornell.edu/cfr/text/14/25.255), it must be shown at VDF/MDF that the longitudinal trim can be actuated in the airplane (https://www.law.cornell.edu/cfr/text/14/25.255) nose-up direction with the primary surface loaded to correspond to the least of the following airplane (https://www.law.cornell.edu/cfr/text/14/25.255) nose-up control forces:

(1) The maximum control forces expected in service as specified in §§ 25.301 (https://www.law.cornell.edu/cfr/text/14/25.301) and 25.397.

(2) The control force required to produce 1.5 g."


Other than the fact that the plane doesn't appear to meet these requirements, then blame the pilots at your gratuitous leisure, but know that under the conditions that the crew had, it is unreasonable to blame the pilots for the deficiencies that are evident in the certification standard, the application of the deficient certification standards, and the resultant unfortunate design choices, and finally, the reticence to train the flight crew on a known area of problematic compliance, the reason that MCAS was incorporated in the first place.

The crew are the result of the system that we have all collective responsibility for, the regulator, manufacturer, airline, TRTO's, and passengers. It is an example of the inherent resonance of the system, no particular failure was necessary by overt action, it was inherent in the assumptions of all users as to what the real world was doing, vs reality.

If you need to blame pilots for being the result of the problem, than know that it doesn't result in any increase in system safety as a consequence.

An old Persian saying:

"Arrogance is the capital stock of misfortune",
Pand-Namah Tasnif Saih Sa'di Sirazi, A Compendium of Ethics, translated from the Persian of Sheikh Sady of Shiraz, (1788)

The NTSB had the common courtesy of incorporating the human in the loop for Sully, yet now for ET and Lion it is apparent that it is only reasonable for a certain group of pilots to be considered to be human factors in the loop. That is ethically unjust and shows the inherent bias that exists in the observers and those that pass judgement from the safety of their laz-e-boys.

That is a very dense statement I confess I do not know what you are trying to say, but I guess it is in defence of the pilots. I do not intend to attack those poor guys; they were obviously out of their depth and should never have been in a position to fly as crew in the first place. I would have to place the blame for that on their airline that did not see to it that their crews were qualified. It does not change the fact that both MAX accidents were pilot error, solely and completely. The failure of the MCAS was the initiator but both airplanes were flyable and the crews failed to fly them; giving up in one case and failing to control speed by reducing the throttles in the other. Any confusion was self-induced and in no way a fault of Boeing or the airplane design. Obviously if the MCAS system, which works in the background, had been explained, most pilots would not have understood and would be even more confused than they are now. There was no need to know why the trim was running away; all the crews had to do was follow the checklist. Narrowing down the MCAS system for attention after landing.

The aircraft does meet all regulatory requirements, the MCAS system was provided to make it fly like its brethren and had no effect on stall speed or handling when it was working properly and when it failed did not need any action other than as a trim failure, which is already a procedure covered in training and practiced regularly (or should have been). The MCAS failure did not bring those aircraft down; poor flying skills did that. If we don't address that as the biggest problem we will see many more failures that will kill many more people. They deserve better.

If you are suggesting that it is OK for a properly trained crew to lose control of their aircraft because they had an unusual situation on their hands then we might as well give up now and get those horses and oxen out of their stalls and hitched up to the wagons before we risk any more passengers in those dangerous sky chariots.

It is not that long ago that pilots with only a few hundred (or less) hours were flying aircraft like the Lancaster and Fortress in war, with parts blown off by cannon fire. You better believe those guys did not give up. You would not have heard them blaming Boeing.

[jumbomax11]

boofhead;

Be careful with guys like Boofhead, Yanrair and others!
Its always easy to say they should have done this or that and could have saved the aircraft easily due to better training and pilot skills!
It was the combination of failures which contributed to these accidents, beginning with AOA Sensor failure, the airspeed unreliable, stickshaker, stall warning and lots of red lights and warnings, all within a short time and in low altitude.
Then came the MCAS, which most did not know about and which was not mentioned by Boeing in the manuals.
In this situation your best strategy will fail and then you may forget or disregard things like speed or so
I bet, most of you guys couldn't save the aircrafts in this extremely complex and unexpected situation!
If you think about having the whole scenario in the simulator, early morning shift without briefing, most if not all crews would have failed to save this.
Of course now, after everybody discussed this at length you having a big advantage to the crews who lost their live.
And of course, not everbody is a Chuck Jaeger or a "Sully"
By the way, in my view the landing in the hudson was a "piece of cake" compared to the scenario of this two accidents!
In my view it is not enough by Boeing just to do some software changes, but the AOA sensor design with only two independant AOA's should have been overworked as well!

[fdr]

Boofhead; "The aircraft does meet all regulatory requirements, the MCAS system was provided to...."

nonsense.

The aircraft did not meet the rules under Subpart D, and that is the underlying issue. The general comments to date have been related to Subpart C, as there is a failure of the rules to provide adequate protection, just as was the case with AA587, where what was assumed by the industry was not so in reality. In all cases, a situation that requires both pilots on the controls to recover is not compliant, nor is having loads that exceed the momentary force loads to be applied by a single pilot, nor is it acceptable for the aircraft to require exceptional skill or strength.

(c) It must be shown that after any single failure of the stability augmentation system or any other automatic or power-operated system—
(1) The airplane is safely controllable when the failure or malfunction occurs at any speed or altitude within the approved operating limitations that is critical for the type of failure being considered;

must permit initial counteraction of failures of the type specified in §25.671(c) without requiring exceptional pilot skill or strength, by either the deactivation of the system, or a failed portion thereof, or by overriding the failure by movement of the flight controls in the normal sense.


and my favorite

(a) A warning which is clearly distinguishable to the pilot under expected flight conditions without requiring his attention must be provided for any failure in the stability augmentation system or in any other automatic or power-operated system which could result in an unsafe condition if the pilot were not aware of the failure. Warning systems must not activate the control systems.

Boof', you mention having control issues, so have I; I have landed a 4 engine aircraft without elevators, and I have landed an aircraft after a mid air collision. I don't believe that in either of those cases was it reasonable to have to rely on either the pilot skill or exceptionalism to survive. Both of those aircraft were military so the rules were different, however, after 20,000 additional hours on Boeings and Airbus, I don't believe that it is acceptable to rely on the pilots achieving something that has not been part of their training. Had they done so, then kudos, but don't shoot the messenger, the crews herein were the product of the training system that we have in the real world, and that is the way it is. It is not acceptable to assume that they would be a Chuck Yeager, Bob Hoover, Neil Williams or similar. What on earth do you expect from a 200hr co pilot in the way of support? What do you expect from a product of the current Part 61 syllabus, MCC shambles under FAR or EASA FCL? This is not regional, skin colour or religion based, we have just seen a fairly serviceable NG get seaplane time recorded, just as happens in Indonesia, Chukk, and various other places, including the Bahamas, etc.

The industry is adequate, not much better than that. You cannot bitch about a crew that is confronted with a complex issue that still confounds the manufacturer and regulator 9 months later, and state with a clear conscience that the problem begins and ends in the cockpit. If you show proof that the crew had been trained competently in runaway trim, of dealing with a stabiliser that was so far out of trim that it needed unloading to be reset, that the crew had sufficient altitude to unload a full nose down trim stab before impacting the ground, that the OEM told them of these latent defects in their aircraft design, that the airline had done so, that they had been checked to such a level?

I am angry; I am angry as I have flown Boeing products for nearly 40 years, and the only aircraft that had any discussion on stab airloads was not a Boeing. I have done out of envelope flight test of the B737 and was not aware of the issue. I am angry on behalf of the flight crew that you appear to assume should have skills well in excess of that trained and checked by the system. Personally, I have flown biplanes, WW2 aircraft, and heavy military singles as well as jets, I accept the constraints of those aircraft, as I now fly them as experimental, restricted or limited category, where the basis of their certification is understood by the words in the 21 Subpart H applicable statements. These aircraft do not provide the level of airworthiness that comes from Part 25, and that is fine.

Further comment:
The industry trains to a minimum standard, that is acceptable to the regulator. The airlines could train to higher standards, however, the competitive nature of the industry precludes undergoing astronaut type training for a regular line pilot. The line pilot gets to see components of a training matrix that covers the usual suspects, a fault with no FDE, faults with FDE and requiring reset of a system, faults that degrade performance, faults that degrade handling qualities. We get to practice ILS's which we do every day, and occasionally train on approaches that statistically end badly. We get to do RTO's, OEI's and the usual basics. Often these are assumed to be the limiting case but are not so. The pilots enter the system with varied background, from those that cleaned planes to go fly, or pumped gas for them, to those that the govt paid to do so, and those that could afford training by other funding. Sometimes the airlines HR department is the source of the feed stock and the processing of the new hire pilot. We see former military pilots in the same course as a baron pilot or a 200hr wet CPL/IR/ME ticket. The system trains these people to go fly low viz procedures down to CAT IIIB in short order, with LVTO and similar points of interest. The guys and girls generally do a credit to their background, and cope with what is thrown at them well. In many countries, they get paid less than subsistence wage and are or food stamps at that time. These people fly the high value payload, anyones loved ones from A to B in weather that includes thunderstorms, squalls, snow, hail, rain and shine. They turn up and undergo training as provided by the company. They are not responsible for what the company trains them on, they are the recipient of the training. If there is a deficiency in their training, don't blame the dead crew in the bottom of the smoking hole for not being trained to a level that would ensure that they can cope with unknown and unexpected events.

Every day around the world, the system generally works. It could be better, but making it better is not the responsibility of the 200hr copilot or 4000 Captain, they are the result of the system not the cause. If you are able to deal with every situation that may come along, then great for you. A number of pilots can do that, many will get close, and many won't deal with situations that have not been trained.

38 years of safety and accident investigation in the military and airlines, and the main takeaway IMHO is to keep things simple, and to understand that crews faced with events often do not respond as they do in the simulator.

[Loose rivets]

Gosh.

That's all I could say for a moment. I don't think it's a case of having to choose between fdr and boofhead's posts, but one of again absorbing the vast width of the chasm between strongly held views.

fdr's post seems to give damning evidence that Boeing didn't come close to fulfilling the requirements but equally, boofhead shouts the truth. Nobody feels more strongly than I do for the ET FO, a kid living his dream, which suddenly turned into a nightmare. Still, it seems for one so inexperienced, he acquitted himself rather well. He'd have been a fine 3rd pilot, but to have this lad and a captain who's bulk experience seems to have been as FO on another type, then that aircraft was not carrying the much needed executives at the helm.

[Fly Aiprt]

Jumbomax11 and fdf,
Thank you for your posts, which reflect sound insight and airmanship.
Many other posts here, from people who according to their published pedigree, should really know better and be a bit less affirmative in their appreciation of the deceased crews. Especially since we don't know yet what exactly happened in the cockpits.
So many crystall ball quarterbacks, even though we still don't know exactly what this MCAS function could actually do.

And maybe Boeing didn't quite know either before the crashes.
300+ flight test hours seems quite a long time to correct a simple "it's just the pilots" event. Things might not be so straightforward after all...

[Loose rivets]

I don't want to leave this mornng's session having given the impression I'm biased to one 'side' or another. I'm not. I'm certain that Boeing will be held accountable for numerous shortfalls, but I'm equally certain the basic flying ability of some modern crews is woefully inadequate. They are just pressing on with their careers as best they can, it's the system that's wrong.
I can not imagine being in command of the MAX without the kind of background I had. Masses of empty sectors, and flying with people who loved to find out just what the aircraft would do. Neither of these scenarios happen much these days. Bums in seats and an electronic prefect connected to the fleet manager's office - where the SOP's line the shelves. Not my world, and not a background that can be simulated by a box on stilts.
In later copies of Handling the Big Jets, Davis (more or less) pleaded for crews to have an aircraft that they could throw around. A big stable electronic office teaches little.

[MurphyWasRight]

The MCAS kicks in, the nose gets heavier. You pull, and trim a bit. The MCAS kicks in again, the nose gets quite heavy, you pull and trim - more, for zero forces - to negate both of the MCAS inputs. If for nothing just to relieve the muscle tension.

Is it the shared view here, that neither of the doomed crew did the above? That they all instead of a good thorough spin just made a couple of "blips" and watched the A/C in VMC hit the ground? While pulling with possibly all four hands on the yokes, fighting the 4x increased elev feel computer and still neither of them touched the rocker switches to relieve that physical pressure, save for those blips?
(My boold in above, times are approximate due to FDR presentation).
Known facts from, report.
Airspeed at start of first MCAS input 250 kts.
MCAS applied 9 seconds ND trim the ET pilot applied 3 seconds NU trim 6 seconds later.
MCAS acitvated 5 seconds after that but was interrupted at 6 seconds by 9 seconds NU trim. (possibly interrupted by trim cutout)

Total MCAS 15 seconds ND total pilot NU 12 seconds left the aircraft severely out of trim and just under VMO in under 40 seconds and likely unrecoverable using manual/mechanical trim.

Above is not "blips" those occurred only at end when electric trim was re-activated.

[safetypee]

Loose rivets, # 135,
Your certainty about the technical aspects is not necessarily the same certainty about pilot performance. Technology, aircraft design, and manufacture, can be judged against hard requirements, whilst humans have no published requirements for their ‘construction’, and where output performance is judged by other, ill-defined humans, in situations seldom related to extreme events.

Returning to the thread topic - trim runway procedure. It appears that knowledge of the procedure and training has decreased in recent years, with new variant aircraft. Yet technical views (# 105 https://www.pprune.org/showpost.php?p=10479475&postcount=105 (https://www.pprune.org/showpost.php?p=10479475&postcount=105)) question the increasing difficulty or effectiveness of the procedure in these newer variants.
These together with the lack of definitive response with quantifying line experience, only add to the unknowns in this topic.
Many test flights, revised revisions of the proposed modification, identification of a simulator discrepancy, and an external review of the procedure across previous variants.

Little or no certainty in any of these.

Not exactly the distinction between science and fiction; but not to judge a book (or person) by its cover ;)

[LowObservable]

But.......who will write the reports? National authorities of the affected airlines.

Who are, of course, not "western".

The number of posts on these pages from boofhead, 737 Driver, yanrair et al., making the same point over and over again, must now be in the hundreds. (737 Driver averaged four-plus posts a day in his meteoric career, then abruptly vanished without a cry.) The accident aircraft were "flyable". Yes, but they quite clearly became less flyable by the second, as long as the crews failed to do the right thing. The crews did not follow correct procedures, Well, they were confronted with a rapidly worsening defect that they'd never been trained to recognize. Properly trained, competent pilots, not "children of the magenta line" should have coped anyway. Really? The simple fact is that as automated aircraft and simulator training have proliferated, and as the number of hours required to enter the right seat has declined, air safety has improved. The final accident reports will be a whitewash, err "westernwash". Hmm, cui bono here?

Why all this repetition? I am tempted to listen to the advice of that great strategist Auric Goldfinger: Once is happenstance, twice is coincidence, and...

[Fly Aiprt]

Returning to the thread topic - trim runway procedure. It appears that knowledge of the procedure and training has decreased in recent years, with new variant aircraft. Yet technical views (# 105 https://www.pprune.org/showpost.php?p=10479475&postcount=105) question the increasing difficulty or effectiveness of the procedure in these newer variants.


For those that performed trim runaway training in the sim, how was the exercice organized ?
Did the flight sim instructor throw in a surprise trim runaway in the middle of some other procedure, or was it just a matter of "now to the runaway trim", "Top, run the runaway drill !", "Good show, next exercice..." ?
Not exactly the same thing, is it ?
Additionally, any runaway would result in some degree of out-of-trim, otherwise that would not be a runaway. What degree of mistrim did you find manageable with the wheels ?
There must be a limit, albeit in the sim ?

[yoko1]

Yes, but they quite clearly became less flyable by the second, as long as the crews failed to do the right thing.



I would suggest that you have this backwards. The longer the pilots flew through this malfunction (i.e. by applying trim with the yoke switch to counteract MCAS), the easier it was to understand what was going on. After about the 20th or 30th time you have to put in nose up trim only to watch MCAS put in nose down trim, I think even the most minimally trained crew could figure out that perhaps turning off the trim cutout switches was the reasonable course of action. The first Lion Air crew got this right. The Captain of the second Lion Air got this right until he turned the aircraft over to his First Officer and mistakenly assumed that the FO would continue to offset the MCAS inputs. The Ethiopian flight seems to be the true anomaly with a Captain who was by all appearances uncomfortable with hand flying and an FO who really didn't have the experience to jump in there and assist the Captain.


The simple fact is that as automated aircraft and simulator training have proliferated, and as the number of hours required to enter the right seat has declined, air safety has improved.



While the overall safety stats has improved, crew errors are becoming an increasing factor in the accidents that do occur. Some of this is due to the same human factors that have been around since the Wright Brothers, but some can be attributable to an increasing reliance on automation as a substitute, as opposed to a compliment, to basic flying skills. The fact that Ethiopian Civil Aviation Authority had no problem granting a 160-hour pilot a license to act as First Officer in a 737 ought to give everyone pause.

[Smythe]

On the subject of trim, I saw that the FAA/EASA information on thumb switches on the MAX, which are trim limited, and that operations at the edge of the envelope would need to be manually trimmed.

Why would there need to be a limit on the thumb switch?

[LowObservable]

While the overall safety stats has improved, crew errors are becoming an increasing factor in the accidents that do occur.

The preponderance of the evidence, it's true, is that the modern, automated and multiply-redundant airplane breaks less often than its tab-and-cable ancestor. Also, since the 1950s, we've stopped expanding the commercial airplane's flight envelope and focused on making it more reliable and more efficient. We have not re-engineered the human being in the same way.

Nonetheless, there's no evidence that the rate of catastrophic "crew errors" (see below) relative to the number of flight cycles has increased. That suggests that the "magenta line" theory of declining skills may be flawed.

Moreover, what people call a "crew error" usually isn't. It's an indication that crew selection, training and maintenance of competency fell short of what was required to handle an off-nominal situation, and it's consequently related to the degree of abnormality that faced the mishap crew.

Now, I am not sure that even the FTFA-fundies here would argue that the unwarned-against activation of MCAS - a running-in-background gadget that commandeered the most powerful effector on the airplane - wasn't quite severely abnormal. And did it occur on a highly automated airplane? Negatory, sir. It afflicted a Topsy-developed hybrid of a simple 1960s servo-mechanical jet with a 21st-century digital overlay.

[hec7or]

LowObservable
A very astute post Sir, also, the fact that the modern equipment is very reliable in comparison to that of the original 1960 era prototype has the unintended consequence that crew only see non-normal events every six months in the simulator and very rarely see real live technical problems in the aircraft where they are faced with all the additional distractions provided by ATC/Cabin Crew/Pax/Ops/Environmental etc. I've yet to see a simulator that can accurately reproduce the non technical distractions.

[yoko1]

LowObservable
A very astute post Sir, also, the fact that the modern equipment is very reliable in comparison to that of the original 1960 era prototype has the unintended consequence that crew only see non-normal events every six months in the simulator and very rarely see real live technical problems in the aircraft where they are faced with all the additional distractions provided by ATC/Cabin Crew/Pax/Ops/Environmental etc. I've yet to see a simulator that can accurately reproduce the non technical distractions.

I don’t think we are terribly far apart in our assessment here. The increased use of automation has demonstrable safety benefits, however, more automation should actually increase the pilot training requirements, not lower them. It used to be that it was enough to know how to fly in a low automation world because that is all we had. Now we need to know how to fly in both high and low automation environments depending on how the circumstances play out. Unfortunately, in a continuing effort to minimize training costs, one set skills is increasingly being sacrificed because the other is viewed as good enough for most situations.

Believe me, I understand how it is natural for pilots to get defensive when suggestions of crew error are tossed about. However, as I have previously stated, a crew’s performance is intimately related to their training, experience, and environment - not all of which they have much control over. I think observations regarding the crew’s performance is really more an indictment of the system that put them in that cockpit than the individuals themselves. Oddly, bending over backwards to overlook crew performance issues is unwittingly playing into the hands of airlines who wish to minimize their pilot labor costs, both in the experience they demand and in the training they subsequently provide. I guess I just don’t get why on one hand it is very easy to heap scorn on Boeing for designing the MAX on the cheap and yet give a pass to airlines who want to hire and train pilots on the cheap.

[yoko1]

On the subject of trim, I saw that the FAA/EASA information on thumb switches on the MAX, which are trim limited, and that operations at the edge of the envelope would need to be manually trimmed.

Why would there need to be a limit on the thumb switch? I thought I saw this covered elsewhere, but here’s my understanding. First, the yoke trim switches are only limited in how far nose down they can move the stab. There is no limit on moving the trim BACK toward the “green band.” I suspect the reason for this has to due with the fact that the only time one would need to trim that far toward the forward limit would be in a certain unusual flap, airspeed and aft c.g. combinations. In generally, when an aircraft starts approaching its aft c.g. limit, the handling characteristics get a bit more sensitive about the pitch axis. I suspect that Boeing wanted to limit how quickly trim could be applied toward the nose down limit in this region.

[LowObservable]

Moreover, what people call a "crew error" usually isn't. It's an indication that crew selection, training and maintenance of competency fell short of what was required to handle an off-nominal situation, and it's consequently related to the degree of abnormality that faced the mishap crew.

Now, I am not sure that even the FTFA-fundies here would argue that the unwarned-against activation of MCAS - a running-in-background gadget that commandeered the most powerful effector on the airplane - wasn't quite severely abnormal. And did it occur on a highly automated airplane? Negatory, sir. It afflicted a Topsy-developed hybrid of a simple 1960s servo-mechanical jet with a 21st-century digital overlay.

Now, let's take this further. "Degree of abnormality" compared to what? If it's "compared to what crews are used to in non-Topsy, post-1980-certificated aircraft" then we have a genuine training challenge.

[edmundronald]

Boofhead; "The aircraft does meet all regulatory requirements, the MCAS system was provided to...."

nonsense.

The aircraft did not meet the rules under Subpart D, and that is the underlying issue. The general comments to date have been related to Subpart C, as there is a failure of the rules to provide adequate protection, just as was the case with AA587, where what was assumed by the industry was not so in reality. In all cases, a situation that requires both pilots on the controls to recover is not compliant, nor is having loads that exceed the momentary force loads to be applied by a single pilot, nor is it acceptable for the aircraft to require exceptional skill or strength.

(c) It must be shown that after any single failure of the stability augmentation system or any other automatic or power-operated system—
(1) The airplane is safely controllable when the failure or malfunction occurs at any speed or altitude within the approved operating limitations that is critical for the type of failure being considered;

must permit initial counteraction of failures of the type specified in §25.671(c) without requiring exceptional pilot skill or strength, by either the deactivation of the system, or a failed portion thereof, or by overriding the failure by movement of the flight controls in the normal sense.


and my favorite

(a) A warning which is clearly distinguishable to the pilot under expected flight conditions without requiring his attention must be provided for any failure in the stability augmentation system or in any other automatic or power-operated system which could result in an unsafe condition if the pilot were not aware of the failure. Warning systems must not activate the control systems.

Boof', you mention having control issues, so have I; I have landed a 4 engine aircraft without elevators, and I have landed an aircraft after a mid air collision. I don't believe that in either of those cases was it reasonable to have to rely on either the pilot skill or exceptionalism to survive. Both of those aircraft were military so the rules were different, however, after 20,000 additional hours on Boeings and Airbus, I don't believe that it is acceptable to rely on the pilots achieving something that has not been part of their training. Had they done so, then kudos, but don't shoot the messenger, the crews herein were the product of the training system that we have in the real world, and that is the way it is. It is not acceptable to assume that they would be a Chuck Yeager, Bob Hoover, Neil Williams or similar. What on earth do you expect from a 200hr co pilot in the way of support? What do you expect from a product of the current Part 61 syllabus, MCC shambles under FAR or EASA FCL? This is not regional, skin colour or religion based, we have just seen a fairly serviceable NG get seaplane time recorded, just as happens in Indonesia, Chukk, and various other places, including the Bahamas, etc.

The industry is adequate, not much better than that. You cannot bitch about a crew that is confronted with a complex issue that still confounds the manufacturer and regulator 9 months later, and state with a clear conscience that the problem begins and ends in the cockpit. If you show proof that the crew had been trained competently in runaway trim, of dealing with a stabiliser that was so far out of trim that it needed unloading to be reset, that the crew had sufficient altitude to unload a full nose down trim stab before impacting the ground, that the OEM told them of these latent defects in their aircraft design, that the airline had done so, that they had been checked to such a level?

I am angry; I am angry as I have flown Boeing products for nearly 40 years, and the only aircraft that had any discussion on stab airloads was not a Boeing. I have done out of envelope flight test of the B737 and was not aware of the issue. I am angry on behalf of the flight crew that you appear to assume should have skills well in excess of that trained and checked by the system. Personally, I have flown biplanes, WW2 aircraft, and heavy military singles as well as jets, I accept the constraints of those aircraft, as I now fly them as experimental, restricted or limited category, where the basis of their certification is understood by the words in the 21 Subpart H applicable statements. These aircraft do not provide the level of airworthiness that comes from Part 25, and that is fine.

Further comment:
The industry trains to a minimum standard, that is acceptable to the regulator. The airlines could train to higher standards, however, the competitive nature of the industry precludes undergoing astronaut type training for a regular line pilot. The line pilot gets to see components of a training matrix that covers the usual suspects, a fault with no FDE, faults with FDE and requiring reset of a system, faults that degrade performance, faults that degrade handling qualities. We get to practice ILS's which we do every day, and occasionally train on approaches that statistically end badly. We get to do RTO's, OEI's and the usual basics. Often these are assumed to be the limiting case but are not so. The pilots enter the system with varied background, from those that cleaned planes to go fly, or pumped gas for them, to those that the govt paid to do so, and those that could afford training by other funding. Sometimes the airlines HR department is the source of the feed stock and the processing of the new hire pilot. We see former military pilots in the same course as a baron pilot or a 200hr wet CPL/IR/ME ticket. The system trains these people to go fly low viz procedures down to CAT IIIB in short order, with LVTO and similar points of interest. The guys and girls generally do a credit to their background, and cope with what is thrown at them well. In many countries, they get paid less than subsistence wage and are or food stamps at that time. These people fly the high value payload, anyones loved ones from A to B in weather that includes thunderstorms, squalls, snow, hail, rain and shine. They turn up and undergo training as provided by the company. They are not responsible for what the company trains them on, they are the recipient of the training. If there is a deficiency in their training, don't blame the dead crew in the bottom of the smoking hole for not being trained to a level that would ensure that they can cope with unknown and unexpected events.

Every day around the world, the system generally works. It could be better, but making it better is not the responsibility of the 200hr copilot or 4000 Captain, they are the result of the system not the cause. If you are able to deal with every situation that may come along, then great for you. A number of pilots can do that, many will get close, and many won't deal with situations that have not been trained.

38 years of safety and accident investigation in the military and airlines, and the main takeaway IMHO is to keep things simple, and to understand that crews faced with events often do not respond as they do in the simulator.

Sir,
I have great respect for your experience. However, do you seriously believe that an "average" reader of this forum isn't already aware of all of this? The problem is not realizing the industry has pervasive issues, it is the improbable expectation that the people who caused the systemic failure will fix it. Aircrews aren't going to get more competent, but better automation design and a return to a reasonably honest and evenhanded certification process are certainly feasible goals, which would be hurried along a bit by the designation of some senior level scapegoats at the FAA and Boeing.

[Water pilot]

. I guess I just don’t get why on one hand it is very easy to heap scorn on Boeing for designing the MAX on the cheap and yet give a pass to airlines who want to hire and train pilots on the cheap.
I don't think the issue was that Boeing was doing anything on the cheap, it would have cost absolutely nothing more to have the MCAS system be a bit more failsafe-ish by comparing the two sensors. The basic issue is that Boeing promised something that was impossible, an aircraft functionally identical to the 737-NG but with larger engines in a different place. They ended up using software to simulate a 737 on an airframe that pretty much anybody could see would have different aerodynamic characteristics. They didn't do this to save money, they did it to save development and certification time in order to get a desperately needed product to market. The software fix was seductive -- it was elegant, simple, and Boeing had already used software to deal with a potential program-ending aerodynamic flaw in a previous model.

The desperate need for the MAX to be "just an upgraded NG" led to an engineering/management problem known as "the Emperor's new clothes." Anything that violated that basic assumption is not acceptable; they apparently went as far as to reorganize the test pilots out of the development program when they raised concerns. Using two sensors would have meant admitting that the Max was NOT an upgraded NG because if the sensors disagreed you had to turn off MCAS which meant that now you have different (and non conforming) flight characteristics. Rather than document the issue, they swept it under the rug and pretended that it wasn't there. This goes for what they told the pilots as well, which was nothing that would upset the party line. Refusing to acknowledge that the Emperor is naked even persists after the accident; this was not a computer failure or a programming flaw, it was a trim runaway like could happen on any 737. Why? Because the MAX is just an upgraded NG, that is why.

Now apparently even that approach has bitten them in the rear end, as by insisting that the accidents (!) were simply mismanaged trim runaways the obvious question is "how do you properly manage a trim runaway?" and the answers are not looking good for either the NG or the MAX. It doesn't help at all that the simulators (which is the only place to practice this very dangerous condition) apparently do not reflect how hard the procedure is in real life. At some point even the most dedicated Boeing FTFA supporter is going to have to stop suspending disbelief and admit that this was a pretty big engineering snafu, and not pilot error.

[fdr]

Ed, this forum is open presumably in the furtherance of aviation centric matters, which include safety, design, operation and training as some aspects. Opinion flows relatively freely and that freedom results in all views being presented, the loudest and most persistent being accorded column inches on the page.

The industry overall works, it has bad days and they are catastrophic for the people concerned, but less so for the industry at large. Passengers and shareholders have voted with their check books to drive the industry in the direction it has gone. That direction has resulted in an explosion of capacity, routes and frequencies, resulting in a demand for flight crew that places pressure on supply of trained personnel. Training standards meet financial bottom lines every day. The regulatory system has been under stress for a long time, and competition for competent staff places strain on the regulator capacity. They cope, as does everyone else.

The OEM is also in a competitive industry, and deals as best they can to produce a product that can compete. The engineers doing design have firewalls to assure the ODA DOA process remains functional. For the MCAS it appears to have slipped a cog. Each part of the system includes humans working under stress, and making deliberations under uncertainty. If we miss out in the imagination to cover all eventualities in a failure mode analysis before the fact, then that is the limit of being human.

Blaming flight crew for not being competent in a dynamic complex event does not improve the long term system reliability. Blaming a 200hr FO, or a 4000hr Capt for not being chuck yeager does not cure the problem. Simplifying procedures through strengthened risk analysis, and better system design flowing from more robust faikure mode analysis is a path forward but doesn't happen quickly. The industry will put a bandaid on the problem with specific fault mitigating training, and that will do in the short term along with better event centric rectification.

The training for all conceivable and inconceivable events for the crew doesn't get done within the cost base of the industry as it stands.

This forum has had numerous comments decrying the competency of the flight crew in these events, contending they are primary causation of the outcome. It is unfair to do that in this case IMHO, and beyond that, the assumption of goodness in those that consider that the fault would have been easy for a competent crew to deal with is potentially a risky assumption. We can hope that following comprehensive review, system redesign,the training that results will increase the likelihood of a successful outcome by any flight crew, not just the Yeagers out there. At that point, if the crew cannot cope with the same problem, then there is a possible crew issue. Before that point, the failure is global. The ability of training reinforcement to mitigate operational risks has a patchy record, we still plant planes in the rough at both ends of the runway, from all cultures and nationalities.

[Bidule]

I have had this problem (runaway trim) and it was difficult to fly the airplane but I am still here so it was not impossible. I did not give up and flew the airplane to the ground with full nose down trim and because of a broken trim cable, no way to reverse the problem. I also flew the 737 for thousands of hours (although never had the trim runaway on that aircraft). I am not an "armchair" pilot and I do know how to fly and how to perform an emergency checklist. I am appalled at the lack of professionalism shown by the pilots in the two 737Max aircraft and even more appalled at the way so many on this thread are preferring to blame Boeing rather than the real cause of the tragedies because of political correctness. If they get their way they would put Boeing out of business and who would benefit then?

No aircraft is immune from failures of some type, and it is the pilot's job to fly it nevertheless and to keep the people who are placing their trust in him/her safe by at the least maintaining an average level of skill and knowledge. Which is all it takes. You don't have to be a super hero.

Fix the real problem. The human element. Take it as a warning of what will happen if we continue to dumb down (to the lowest common denominator as has been suggested we should be doing). Maybe we should be replacing the pilots with computers. They could not do any worse.

If it was as obvious and simple as you try to convince us:
- why did ALL the CAAs ground the aircraft?
- why did Boeing already fly 300 hours of additional test flights?
- why has Boeing not yet provided any fix to the FAA, which was expected six weeks after the Lion Air accident, and then in April 2019, and then before the CAAs meeting last week (nothing yet arrived)?

When you give me reasonable answers to these basic questions, I shall then support you on the training which is an issue, everywhere in the world, but likely not the main issue for the two B737Max accidents.

Rgds

[yoko1]

At some point even the most dedicated Boeing FTFA supporter is going to have to stop suspending disbelief and admit that this was a pretty big engineering snafu, and not pilot error.

I don’t recall a single person denying that there was a huge problem with the MCAS design. This is not an either/or situation. It is NOT a case that all the fault lies with Boeing OR all the fault lies with the crew. There are issues with both. The MAX/MCAS design issues are being given the most intense scrutiny of any commercial aircraft that has been produced in recent history. I don’t think we need to worry that something is going to slip by the army of engineers, regulators, and lawyers that are circling the good ship Boeing. However, if in all the determination to pin these accidents on Boeing, and only on Boeing, we ignore the what the data is also saying about the level of crew proficiency, then we just help perpetuate a culture that is in a seeming race to the bottom to see how low airlines can set the bar for pilot training standards. I’m sure those airlines are more than happy for the cover as they funnel resources away from better training and into the pockets of investors and managers.

[Wrightwing]

I find it moderately interesting that the case chosen for evaluation is runaway nose up trim, which is an urgent stall hazard. Presumably nobody in 1982 could visualise the hazards of runaway nose down trim, perhaps due to the limited range of trim travel allowed by the autopilot in the flaps down condition. As the article notes, assumptions made five decades ago, are still propagating through today's 737 flight controls.
You seem to have missed the sentence "if nose up trim is required". Somebody in 1982, did in fact "visualise (sic) the hazards of runaway nose down trim".

[Loose rivets]

safetypee's reply to a post of mine where I'd more or less divided up the blame between Boeing and, not the pilots per se, but the system in which they flourish - or not.

Loose rivets, # 135,
Your certainty about the technical aspects is not necessarily the same certainty about pilot performance. Technology, aircraft design, and manufacture, can be judged against hard requirements, whilst humans have no published requirements for their ‘construction’, and where output performance is judged by other, ill-defined humans, in situations seldom related to extreme events.

Hmm . . . preaching to the converted. I was still a young man when I had to deal not only with an alcoholic and probably psychotic captain, for weeks, but while a management and training staff that promised and promised to remedy the situation, simply never did. This guy had a long career behind him but still managed to singe the passengers queuing behind the jet pipe and then take off three tonnes overweight in that little BAC 1-11. That's not a mistake. He was just not right, but the manager's lacking was wrong to the point of being sinister. If you've any ideas about Us being better than Them, I could fill in a year's worth of bizarre happenings leading up to me walking out of the best paid job I'd ever had. Ill-defined humans. That's a good term.

Despite spelling out that extraordinary situations can arise with any crew, I still maintain the ET crew were woefully inexperienced. It could be I'm plain jealous. It was 8,000 for PIC and 4,600 for FO when I moved over to the 1-11 after two years on Viscount. I clearly recall something 'clicking' at about 500 hours - at last I felt really at home on type.

Even with an experienced skipper, so much depends on their wellbeing and indeed, how they react when one day they are confronted with an extremely demanding emergency. Most of us need that other pair of experienced hands in those moments.

[boofhead]

If it was as obvious and simple as you try to convince us:
- why did ALL the CAAs ground the aircraft?
- why did Boeing already fly 300 hours of additional test flights?
- why has Boeing not yet provided any fix to the FAA, which was expected six weeks after the Lion Air accident, and then in April 2019, and then before the CAAs meeting last week (nothing yet arrived)?

When you give me reasonable answers to these basic questions, I shall then support you on the training which is an issue, everywhere in the world, but likely not the main issue for the two B737Max accidents.

Rgds

They did not ground the aircraft until forced to by the negative publicity and apparent anger from the public. They did not ground the aircraft because of a fault in the aircraft as it was accepted by those authorities including the FAA until the public pressure from those who were not qualified to apply it but were emoting and not analyzing nor applying scientific reasoning. For example the fact that the pilots of those aircraft did not follow the checklist for the emergency was hardly discussed but it should have been. Why did those crews fail so badly? Were they incompetent? Poorly trained? Inexperienced? To date none of those possibilities have been looked at, even cursorily.

Boeing is doing its job to thoroughly test the airplane. They could not just zip around the pattern and call it good, even if they were sure there was nothing wrong with the design or construction of the airplane. The public, driven by the blood in the water and wanting to bring down Boeing, would never tolerate that. Facts be damned. I still read that the MCAS system was put in the aircraft to prevent a stall when it has nothing to do with that. I read comments by pilots on this forum who buy into the ill-informed and emotive reporting by the media (when will we learn that they have nothing to contribute to the news but their twisted agenda?) that ignore the facts and join the pile-on to destroy the company that has done so much to make aviation the most successful and safe industry and public service in modern times. For what reason? Politics? Ignorance? Follow the leader?

Boeing is working on a fix. They could have provided it on day One. That fix is to leave it as it is. There is nothing they need to do and they will never find anything that would satisfy the great unwashed who do not understand the subject. The airplanes were always flyable. There was always a procedure to fly them safely with the MCAS system not working as it should. There were at least six ways to stop those airplanes from plummeting into the ground out of control. After the investigation is over Boeing will not be able to come up with a fix because there is not a fix available because there is not a design defect or construction error that needs to be fixed. It is like having a car hit a pothole on the road and the driver allows the car to cross the median and kill the people in the other lane by running into them head on. Was the fault the road maintenance crews? The people who issued that driver a license? The tire manufacturer? Or was it simply that the driver did not know how to handle that type of problem and lost control? My daughter nearly did that when she hit a patch of ice that had run over the road from a broken water main in the winter. She was lucky that the other driver immediately drove his car off the road into a ditch to avoid the head on accident because my daughter could not get her car back onto her side of the road. Two of my daughters were on board that car and I could have lost both of them. I could have kissed that other guy, a middle aged chap who had good reflexes, but I had to blame my daughter a little because her first instinct was to slam on her brakes which caused an instant loss of control. She should have steered the car through and braked on the other side. I also know that she was facing something way out of her experience and she did not panic. She got her car under control and nobody was hurt, But these pilots managed to kill over three hundred innocent people despite being trained and qualified, including how to handle this specific problem of runaway trim. There is a difference between blaming a driver of a car who had never been given training on how to handle a sudden skid or had never experienced it before and a professional who had been so trained but failed to recognize the problem and failed to act correctly. Who allowed himself to lose the plot and give up. I would have respect for someone who went down fighting as did the pilot of that FedEx 767, or the 747 pilot in Dubai, even the ValuJet pilot, rest their souls, but to throw a perfectly good airplane into the ground simply because he lacked basic flying skills is not acceptable to me.

Those pilots should not have been there. They did not know what to do. Whether that was their fault or the trainers, or the management, the regulators or the shortage of pilots that is making all of us lower the bar I don't know and if it is not examined and if something is not done to correct the problem when it is identified we can expect to see more of the same.

[reamer]

Couldn't agree more Boofhead

[Bidule]

They did not ground the aircraft until forced to by the negative publicity and apparent anger from the public. They did not ground the aircraft because of a fault in the aircraft as it was accepted by those authorities including the FAA until the public pressure from those who were not qualified to apply it but were emoting and not analyzing nor applying scientific reasoning. For example the fact that the pilots of those aircraft did not follow the checklist for the emergency was hardly discussed but it should have been. Why did those crews fail so badly? Were they incompetent? Poorly trained? Inexperienced? To date none of those possibilities have been looked at, even cursorily.

Boeing is doing its job to thoroughly test the airplane. They could not just zip around the pattern and call it good, even if they were sure there was nothing wrong with the design or construction of the airplane. The public, driven by the blood in the water and wanting to bring down Boeing, would never tolerate that. Facts be damned. I still read that the MCAS system was put in the aircraft to prevent a stall when it has nothing to do with that. I read comments by pilots on this forum who buy into the ill-informed and emotive reporting by the media (when will we learn that they have nothing to contribute to the news but their twisted agenda?) that ignore the facts and join the pile-on to destroy the company that has done so much to make aviation the most successful and safe industry and public service in modern times. For what reason? Politics? Ignorance? Follow the leader?

Boeing is working on a fix. They could have provided it on day One. That fix is to leave it as it is. There is nothing they need to do and they will never find anything that would satisfy the great unwashed who do not understand the subject. The airplanes were always flyable. There was always a procedure to fly them safely with the MCAS system not working as it should. There were at least six ways to stop those airplanes from plummeting into the ground out of control. After the investigation is over Boeing will not be able to come up with a fix because there is not a fix available because there is not a design defect or construction error that needs to be fixed. It is like having a car hit a pothole on the road and the driver allows the car to cross the median and kill the people in the other lane by running into them head on. Was the fault the road maintenance crews? The people who issued that driver a license? The tire manufacturer? Or was it simply that the driver did not know how to handle that type of problem and lost control? My daughter nearly did that when she hit a patch of ice that had run over the road from a broken water main in the winter. She was lucky that the other driver immediately drove his car off the road into a ditch to avoid the head on accident because my daughter could not get her car back onto her side of the road. Two of my daughters were on board that car and I could have lost both of them. I could have kissed that other guy, a middle aged chap who had good reflexes, but I had to blame my daughter a little because her first instinct was to slam on her brakes which caused an instant loss of control. She should have steered the car through and braked on the other side. I also know that she was facing something way out of her experience and she did not panic. She got her car under control and nobody was hurt, But these pilots managed to kill over three hundred innocent people despite being trained and qualified, including how to handle this specific problem of runaway trim. There is a difference between blaming a driver of a car who had never been given training on how to handle a sudden skid or had never experienced it before and a professional who had been so trained but failed to recognize the problem and failed to act correctly. Who allowed himself to lose the plot and give up. I would have respect for someone who went down fighting as did the pilot of that FedEx 767, or the 747 pilot in Dubai, even the ValuJet pilot, rest their souls, but to throw a perfectly good airplane into the ground simply because he lacked basic flying skills is not acceptable to me.

Those pilots should not have been there. They did not know what to do. Whether that was their fault or the trainers, or the management, the regulators or the shortage of pilots that is making all of us lower the bar I don't know and if it is not examined and if something is not done to correct the problem when it is identified we can expect to see more of the same.

What a wonderful post! You deserve a premium from Mr Boeing!

Just some extracts form your post:

"They did not ground the aircraft until forced to by the negative publicity and apparent anger from the public" Until the aircraft was grounded worldwide, the public was not involved nor reacting....

"They did not ground the aircraft because of a fault in the aircraft as it was accepted by those authorities including the FAA" The FAA seems now to have less willingness to accept the aircraft "as is".

"wanting to bring down Boeing" Any evidence of that?

"That fix is to leave it as it is" Even Boeing did not try this one, marvellous!

"But these pilots managed to kill over three hundred innocent people despite being trained and qualified, including how to handle this specific problem of runaway trim." At least for the Lion Air pilots, they cannot have been trained on the consequences of MCAS operation as MCAS was not known by the pilots, NOT INCLUDED in the Boeing's manual; it even seems that FAA was not fully informed of the working details of MCAS.

You should suggest creating a worldwide certification agency and apply to be the Chairman; you have the required talents.

.

[wonkazoo]

"As of November, 2018, any thread containing the words "737" or "Max" will, before being terminated by the moderators and before reaching a maximum of 130 posts devolve to an ongoing argument over whether or not the pilots were solely (or significantly) responsible for the Lion Air and Ethiopian crashes,"

It should be noted that while Wonk is excited to publish Wonk's First Rule, it remains really unfortunate given that this thread raises a critical flight-safety issue, no matter who is doing the flying, and as fdr has (as always) eloquently identified there is (and should be) a long and ongoing discussion about what the ramifications of a horizontal stabilizer that can be frozen in place within the operating envelope of the airplane are for operators and pilots of the 737.

Of all the post-Lion Air threads this is the one that is most critical to stay alive. If you need/want to argue about blaming the pilots I suggest you go to the ET thread, where there are literally thousands upon thousands of posts for you to digest one at a time. Here the discussion should be about the completely anomalous discovery of the inadequacies of the trim system in post Classic 737s, a discovery that places the airworthiness of not just the Max, but the NG in doubt as well.

Warm regards-
dce

[fdr]

"As of November, 2018, any thread containing the words "737" or "Max" will, before being terminated by....
dce


That would be nice.

I don''t see any evidence of posts intending to harm TBC, or their product. EASA raised concerns back with the NG trim system which shows the extent of missing the opportunity that existed. The event highlights the design, certification standards, and, yes, training matrix as well as adequacy of information provided to the flight crew in training and checking.

Bottom line is the flight crew are just the ones left holding the consequences of the global deficiencies. That some crew may be able to handle such an event is not a basis for system safety.

Cheers

[Loose rivets]

I think this is perhaps the most important topic ever to have been discussed on pprune. Some weeks ago I suggested threads dedicated to different facets of the subject. Although Tech Log might normally be appropriate for the technical issues, I wondered if a sticky that could be added to on R& N might be more at hand.

I had hoped there'd be a way to lay out all the technical information so that it could be added to but not constantly repeated. For example, the action and the limitations of the trim switches. The logic here is that the limitations of the trim action has been raised in recent days, and I for one had forgotten the subtleties.
The hidden column switch's modified functionality is another example of a highly relevant and fairly complex issue. But in over 6,000 posts I still have to trace the circuitry to make some sense of a doubtful consensus. Tough to get a clear picture.

I entirely agree the training issues should be separate, though it's inevitable a technical thread cross-referencing will be needed.

And then there's Boeing and the FAA, a major subject of course, but while it would be good to have it focussed in yet another thread, to be able to link to known reference points in the technical thread would be a very useful tool.

I don't know who would do all this work as I doubt an open thread 'sensible use' policy would be free of repeated strong opinion. Yes, I'm one of the guilty ones.

There has been so much good data posted since November, but so many re-postings and confused not-so-new questions make it hard to sort the wheat from the chaff, but as implied, this is perhaps the most important crisis to ever hit civil aviation and it could go on for years. Perhaps it deserves an unprecedented pprune structuring that would work in the long term.

[LowObservable]

Thank you for sharing your anger, Boof.

Goodness. Are we saying that the grounding was driven by "negative publicity"? What, pray, caused that publicity? If your answer is "two closely related total losses of a brand-new airplane" you may take a cookie from my desk. How do you expect humans to react? How do you explain that aircrew unions were among the leaders of a call for grounding?

The media "have nothing to contribute to the news but their twisted agenda?" Hmm, Boof, I bet they're The Real Enemy Of The People too. Or maybe you're just mad that they unearthed Sinnett's comments after crash #1.

And by the way - even as SLF I think your remark about MCAS...

I still read that the MCAS system was put in the aircraft to prevent a stall when it has nothing to do with that.

...is nitpicking at best. MCAS was installed to restore a linear relationship between stick force and AoA, which is required for certification. And why is it required for certification, boys and girls? That's right, to reduce the chances of entering a stall.

Oh, I'm sure you're a great Dad and all, but you live in a part of the world that has hard freezes and you never told your kids how to handle ice?

[BluSdUp]

I get it now Boofhead.
How appropriate.

[boofhead]

I confess I don't understand your objections to what I am saying. If a stall strip comes off an airplane in flight and then the pilot subsequently finds on approach that the wing is dropping, should he give up? Just let the airplane fly into the ground? I would posit that there are pilots out there just waiting for that opportunity. He does not have to know why the wing is dropping all he has to do is react and recover.

If a pilot gets ice on the tailplane and experiences tailplane stalling should he think "I have not been trained to handle this so I just give up?" If a pilot finds that after lift off his airspeed indicator is not working because of ice/tape/bugs/malfunction is he allowed to just give up and throw the airplane into the ground? He has a sudden engine failure, follows the drill but forgets to feather the prop should he just sit there and allow the airplane to roll itself up into a ball? Even distractions in flight have caused the pilot and his passengers to die. All these things have happened and hundreds of people have died as a result, often with professional pilots flying the aircraft.

It is not important why the stab system failed. It could have been a myriad of things. All a pilot has to do is fly the airplane. It happens many times without a problem and we don't even hear about it. Engines fail and pilots do the right thing, they handle icing, mechanicals, recognize subtle incapacitation, low oil pressure, engine failures, prop runaways, incipient stalls, seat belts hanging out of the door, out of balance loading, bird strikes and more and don't decide to kill themselves and their passengers. That is what we expect and deserve from a professional pilot.

Sure we fix the problem of the MCAS. We increase maintenance to ensure the stall strip does not come off. We give the pilots training to handle what we think might happen in his flight, but we can't anticipate everything and therefore we must have professional flight crews who can handle the unexpected and that means they have to be able to fly their airplane all the way to the ground without giving up.

If they fail, we have to be able to see that as not only a warning to build our airplanes better (add stall warning, anti ice equipment, better passenger restraint, fire bottles etc) but also recognize when pilot training has failed. And do better. But if we deny the pilot element and do nothing we better get ready for the body bag companies to increase their stock prices.

[DaveReidUK]

I confess I don't understand your objections to what I am saying. If a stall strip comes off an airplane in flight and then the pilot subsequently finds on approach that the wing is dropping, should he give up? Just let the airplane fly into the ground? I would posit that there are pilots out there just waiting for that opportunity. He does not have to know why the wing is dropping all he has to do is react and recover.

If a pilot gets ice on the tailplane and experiences tailplane stalling should he think "I have not been trained to handle this so I just give up?" If a pilot finds that after lift off his airspeed indicator is not working because of ice/tape/bugs/malfunction is he allowed to just give up and throw the airplane into the ground? He has a sudden engine failure, follows the drill but forgets to feather the prop should he just sit there and allow the airplane to roll itself up into a ball? Even distractions in flight have caused the pilot and his passengers to die. All these things have happened and hundreds of people have died as a result, often with professional pilots flying the aircraft.

While I appreciate that the JT and ET CVR transcripts haven't been made public, I'm going to stick my neck out and predict that the words "I give up" won't feature on them at any point, from any of the four pilots involved.

[Fly Aiprt]

While I appreciate that the JT and ET CVR transcripts haven't been made public, I'm going to stick my neck out and predict that the words "I give up" won't feature on them at any point, from any of the four pilots involved.

What we do know right now is that the control position curves indicate that both ET pilots have kept pulling on the control columns even while being floated off their seats or being thrown into the harness at 0 to -1 g.
Thats hardly giving up, is it ?

[LowObservable]

Boof:

It is not important why the stab system failed.​​​​​:

It didn't. It did exactly what it was designed to do, just at the wrong time.

[reamer]

What we do know right now is that the control position curves indicate that both ET pilots have kept pulling on the control columns even while being floated off their seats or being thrown into the harness at 0 to -1 g.
Thats hardly giving up, is it ?
No, but what they should have been doing at that stage was returning to land after completing the procedure that we all learned from the Lion air crash.

[infrequentflyer789]

No, but what they should have been doing at that stage was returning to land after completing the procedure that we all learned from the Lion air crash.

According to the report they were turning back when the final LOC happened (and they certainly returned to land...). Lion air were also returning when they crashed. Coincidence? - probably, but I would want to look at the possibility that turning contributed in some way to final LOC.

Secondly it might have been what they should have been doing per procedure, but the only other crew to experience MCAS didn't turn back - and they (and their pax) are alive. Coincidence again, or causal?

Thirdly no 737 pilot should have been learning any procedure from Lion Air crash - no new procedures were created.

[Fly Aiprt]

According to the report they were turning back when the final LOC happened (and they certainly returned to land...). Lion air were also returning when they crashed. Coincidence? - probably, but I would want to look at the possibility that turning contributed in some way to final LOC.

Re the ET flight.
Could it be that pilot input to change heading contributed to the AP disengagement ? Those events occurred around 05:39:48...

[fdr]

It is not important why the stab system failed. It could have been a myriad of things. All a pilot has to do is fly the airplane. It happens many times without a problem and we don't even hear about it. Engines fail and pilots do the right thing, they handle icing, mechanicals, recognize subtle incapacitation, low oil pressure, engine failures, prop runaways, incipient stalls, seat belts hanging out of the door, out of balance loading, bird strikes and more and don't decide to kill themselves and their passengers. That is what we expect and deserve from a professional pilot.

....

If they fail, we have to be able to see that as not only a warning to build our airplanes better (add stall warning, anti ice equipment, better passenger restraint, fire bottles etc) but also recognize when pilot training has failed. And do better. But if we deny the pilot element and do nothing we better get ready for the body bag companies to increase their stock prices.

Boof;

1. The JT crew didn't have any advice on the matter.
2. The ET crew had limited guidance provided by the OEM in his all operators notices.
3. The OEM notice didm't reinforce the issue of loss of trim capability on selecting stab trim cutout.
4. The ET crew followed initially the guidance material, and then for reasons to be investigated elected to return the stab trim operation, which then went pear shaped.

One can assume that this crew was trying their best with the information and training they had, and for some reason elected to return the stab to normal operation. I suspect we are going to find that the stab being defeated by airloads on the B737 is substantially worse on the Max/NG than any other type, and that it could even be marginal within the existing out of trim standard which is a lower level of mis-trim than the MCAS can and did result in.

It has taken some months of discussions to indicate the problems of airloads on the mis-trimmed stabiliser, and Max experience of that condition comes down to a single deceased crew, ET302, and possibly the OEM's TPs over the last 3 months. The simulator is stated to not reflect the event correctly, which leaves the MCAB and flight test as the only place that it is likely to evaluate how severe the mis-trim air loads problem really is.

Something caused the guys to reset the cutouts... and I would suggest that it is a mathematical certainty that no one on this forum other than an OEM TP has actual experience with the Max8 mis-trim airloads, so comments on competency, not fighting etc would seem to be unwarranted.

[yoko1]

4. The ET crew followed initially the guidance material


.

Except they really didn’t. The closest they came was the FO shouting “Stab trim cutout”, and then someone flipped the cutout switches before there was any attempt to neutralize the trim. It is not even clear from the CVR transcript that they were executing any “guidance material.” That would have required actually calling for a checklist.

This is about the same level of competence as someone shouting “Fire” immediately followed by someone shutting down engines and firing off halon bottles without any attempt to identify, confirm, and execute the checklist in the way it was designed. There is a reason that we have very specific instructions on how to accomplish non-normal checklists. It has been proven many times in the past that rushing through an emergency procedure can have a bad outcome, and this case was no different.

[Fly Aiprt]

Except they really didn’t. The closest they came was the FO shouting “Stab trim cutout”, and then someone flipped the cutout switches before there was any attempt to neutralize the trim. It is not even clear from the CVR transcript that they were executing any “guidance material.”

To date, no CVR transcript has been released for any of the MAX crashes.

[fdr]

Except they really didn’t. The closest they came was the FO shouting “Stab trim cutout”, and then someone flipped the cutout switches before there was any attempt to neutralize the trim. It is not even clear from the CVR transcript that they were executing any “guidance material.” That would have required actually calling for a checklist.

This is about the same level of competence as someone shouting “Fire” immediately followed by someone shutting down engines and firing off halon bottles without any attempt to identify, confirm, and execute the checklist in the way it was designed. There is a reason that we have very specific instructions on how to accomplish non-normal checklists. It has been proven many times in the past that rushing through an emergency procedure can have a bad outcome, and this case was no different.


Yoko, the OEB doesn't provide a checklist, it provides guidance material and procedures, which in this case had no information that would assist a crew faced with a manual trim overcome by airloads at low altitude in the AND case.

[yoko1]

To date, no CVR transcript has been released for any of the MAX crashes.

https://flightsafety.org/wp-content/uploads/2019/04/Preliminary-Report-B737-800MAX-ET-AVJ.pdf#page9

page 11

Yoko, the OEB doesn't provide a checklist, it provides guidance material and procedures, which in this case had no information that would assist a crew faced with a manual trim overcome by airloads at low altitude in the AND case.

You mean OEM as in “Boeing”? I thought you were referring to the runaway stab procedure, which is published and was discussed in the post-Lion Air AD. If you mean that there was no reference to the problems of manual trimming from a large out of trim state, then yes, that has not been in the 737 manuals for a very long time, and it ought to be restored. That being said the ET crew could have avoided the large out of trim state through the use of the pilot’s yoke trim switch. It was working, but it was not used effectively. If you wish to see what effective use looks like, look at the first Lion Air flight and the first seven minutes of the second Lion Air accident flight before the Captain transferred aircraft control to the First Officer.

[MurphyWasRight]

https://flightsafety.org/wp-content/uploads/2019/04/Preliminary-Report-B737-800MAX-ET-AVJ.pdf#page9

page 11



You mean OEM as in “Boeing”? I thought you were referring to the runaway stab procedure, which is published and was discussed in the post-Lion Air AD. If you mean that there was no reference to the problems of manual trimming from a large out of trim state, then yes, that has not been in the 737 manuals for a very long time, and it ought to be restored. That being said the ET crew could have avoided the large out of trim state through the use of the pilot’s yoke trim switch. It was working, but it was not used effectively. If you wish to see what effective use looks like, look at the first Lion Air flight and the first seven minutes of the second Lion Air accident flight before the Captain transferred aircraft control to the First Officer.
That is not a transcript, it is a carefully crafted summary at best that leaves out a lot of details. Even so

At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and FirstOfficer confirmed stab trim cut-out.
Does not at all sound like someone shouting fire and taking panicked random action.

Also note that the 'lion air emergency AD" casually mentions the possible problems with air loads in a note section and does not at all stress using pilot trim switches, which would be equally catastrophic if a 'stuck relay' trim run-away was happening...

[yoko1]

Murphy,

Care to enlighten us as to how many 737 checklists have the pilots use the stab trim cutout switches? And how many steps come before that particular action was supposed to be taken? I agree it was not random, and it may be a bit strong to say “panicked” (your word, BTW, not mine), but it was hasty, ill-considered, and ultimately fatal.

[yoko1]

.
That is not a transcript, it is a carefully crafted summary at best that leaves out a lot of details.




You actually make a very good point here. The ET302 preliminary accident report was a product of the Ethiopian Ministry of Transport (MOT) which is the government department that oversees the Ethiopian Civil Aviation Authority (ECAA) who are the folks that were responsible for establishing the training and certification standards for Ethiopian Airlines and the Ethiopian Aviation Academy (of which both pilots were graduates). Ethiopia itself does not have the best reputation when it comes to various human rights such as free expression, and its authoritarian and hierarchal government structure is not the type that would welcome any information that might prove embarrassing to itself or its flag carrier. For that reason, it is highly more likely that the MOT would make a “carefully crafted summary” to put the ET302 pilots in the best possible light than the reverse.

I would submit that the Ethiopian MOT has a very strong bias against publishing anything that would call into question pilot training, certification, and/or competency issues. Thus, any statements issued by the MOT regarding flight crew actions or competency should be viewed with the same degree of skepticism as we give toward statements by Boeing regarding the safety of the 737 MAX design and statements by the FAA regarding the integrity of the certification process.

[Fly Aiprt]

https://flightsafety.org/wp-content/uploads/2019/04/Preliminary-Report-B737-800MAX-ET-AVJ.pdf#page9

page 11


I'm afraid there is some confusion here. Your link is pointing to the preliminary report which doen't include any transcript, but only carefully written information on some aspects of the flight.
As MurphyWasRight mentioned, the FO called out Cutout Switches, and the Captain agreed.
As a comparison, carefully reading a final report from the NTSB could help better understand what a CVR transcript is.
It would also show how investigators carefully search for any information before concluding as to the probable causes of the mishap and refrain of jumping to conclusions or putting blame on anyone.

[Water pilot]

I just re-read that link and noticed something interesting to a data person, what does this mean? To me this indicates that the fan speed target was recorded as NAN (not a number) or some other error signal, and I can't figure out how that could be related to unreliable airspeed.

The N1 target indicated non data pattern 220 seconds before the end of recording.

[Bend alot]

Yoko.

One or several of the experienced 737 pilots that have posted along the line of pilots fault.

Said first thing is to hit the cut out switches - not trim to a neutral, them kill the switches.

These comments were made before the simulator deficiencies were made. So these pilots also could have hit the switches and found that it was too far out of trim, for manual trim wheel operation. So what to do now when you expect the wheel to move but it will not move?

You need to maintain power and pitch and your out of trim - with a frozen trim wheel and a few distractions going on. Do you start the "Yo-Yo" procedure at what is a low altitude or turn the switches on to try the trim?

Question - If the column trim switch is held trim up THEN the cut outs are turned back on, would it trim or does the column switch need to be "reset" to neutral then back to nose up?
Why would you turn the cut out trim switches back on, if you were not intending to trim?

[Loose rivets]

This got split from Water pilot's post # 179 Which was:

I just re-read that link and noticed something interesting to a data person, what does this mean? To me this indicates that the fan speed target was recorded as NAN (not a number) or some other error signal, and I can't figure out how that could be related to unreliable airspeed.Quote:
The N1 target indicated non data pattern 220 seconds before the end of recording.




Way back I'd noticed that though of a much shorter duration, the Fuel Flow of the JK flight was the highest it had been since take-off - just before the sudden climb.
.
.
.

[capngrog]

That is not a transcript, it is a carefully crafted summary at best that leaves out a lot of details. ...

That is exactly correct. What has been released to date is not a transcript, but merely a narrative account of cockpit conversations and is not from a transcript of the actual cockpit conversations. Has anyone seen/read a transcript of the CVR tapes? Will such a transcript be forthcoming?

The above question was raised back on 05 May in another thread about the Ethiopian crash. That thread has since been closed, because it had accumulated a bazillion or so posts.

Cheers,
Grog

[yoko1]

10482520]Yoko.

One or several of the experienced 737 pilots that have posted along the line of pilots fault.

Said first thing is to hit the cut out switches - not trim to a neutral, them kill the switches.

I am also qualified on the 737, so I’m familiar with the system and procedures. Whoever said to use the cutout switches without regard to either a published procedure or before attempting to neutralize the trim was wrong - just plain wrong. Perhaps in the old days when pilots were expected to have a greater knowledge of the systems would such a divergence been acceptable. Not so much anymore.

I don’t really see the crew errors as being a case of the pilots personally being at fault, but rather continued evidence that airlines around the world (including, sadly, mine) continue to underinvest in their pilots, by some combination of accepting ridiculously low experience (i.e. the ET302 First Officer) and/or minimal training that is heavy on managing the automation and checking off boxes in the sim and light on managing the aircraft (to include proficiency in hand-flying) and preparation for unusual, out of the box situations.

As far as use of the trim cutout switches, we have to assume the ET crew was either following an established procedure or not. If they were attempting to accomplish the runaway stab procedure (the only one that I know of that uses the cutout switches), then they did it incorrectly leaving the aircraft in a grossly out of trim condition. If they were not following a published procedure and merely grasping at straws, then they were grasping at the wrong straw. The immediate remedy to the MCAS inputs was the yoke trim switch, not the trim cutout switch. Once the trim had been neutralized (or at least close), only then would it have been appropriate to disable all electric trim.

These comments were made before the simulator deficiencies were made. So these pilots also could have hit the switches and found that it was too far out of trim, for manual trim wheel operation. So what to do now when you expect the wheel to move but it will not move?

This is one of the ways in which pilot training has suffered. Even my own airline stopped teaching the runaway stab trim procedure in the sim in the past few years because they considered it so statistically improbable. We’ve had quite a few pilots here get a rude awakening with these accidents. That being said, the only thing really required of the flying pilot was to trim the stab and (in the case of ET302) set a normal power setting. As I have mentioned before, three of the five pilots who actually operated the aircraft with an ongoing MCAS malfunction did exactly that. It was only the second Lion Air First Officer and the Ethiopian Captain who failed to trim effectively against MCAS. So it seems that some of these pilots actually did know how to keep the plane flying. Unfortunately, two of them did not.

You need to maintain power and pitch and your out of trim - with a frozen trim wheel and a few distractions going on. Do you start the "Yo-Yo" procedure at what is a low altitude or turn the switches on to try the trim?

Well, my first answer would be that you would try not to get in this situation in the first place (see above). I mean it is entirely possible to put any aircraft in a position where a recovery is no longer possible, so it is best to avoid not doing that in the first place. The last few minutes of AF447 comes to mind here.

Question - If the column trim switch is held trim up THEN the cut outs are turned back on, would it trim or does the column switch need to be "reset" to neutral then back to nose up?
Why would you turn the cut out trim switches back on, if you were not intending to trim?

I am not aware of any “reset” function for the yoke trim switches. MCAS and Speed Trim will pause for 5 seconds if the pilot trim is used. If they had held the yoke trim switches in the nose up position before turning on the cutout switches, I believe they would have gotten an immediate response. However, by this time they had exceeded Vmo, so there is a real question as to how the stab behaves in this region. A while back there was an article on a blog called (I think) Bjorn’s Corner in which he speculates that the pitch forces were so sensitive at this speed that when the pilots tried to use the yoke trim switches after restoring power, the resulting g-forces were startling that they did not apply sufficient nose up trim before MCAS (which doesn’t care about g-forces) made its final, fatal input. Perhaps if one of the pilots had set an appropriate power setting to keep the aircraft within its certified envelope then they would not have had this issue.

[MurphyWasRight]

[QUOTE=yoko1;10482936]I am also qualified on the 737, so I’m familiar with the system and procedures. Whoever said to use the cutout switches without regard to either a published procedure or before attempting to neutralize the trim was wrong - just plain wrong. Perhaps in the old days when pilots were expected to have a greater knowledge of the systems would such a divergence been acceptable. Not so much anymore.

I don’t really see the crew errors as being a case of the pilots personally being at fault, but rather continued evidence that airlines around the world (including, sadly, mine) continue to underinvest in their pilots, by some combination of accepting ridiculously low experience (i.e. the ET302 First Officer) and/or minimal training that is heavy on managing the automation and checking off boxes in the sim and light on managing the aircraft (to include proficiency in hand-flying) and preparation for unusual, out of the box situations.

As far as use of the trim cutout switches, we have to assume the ET crew was either following an established procedure or not. If they were attempting to accomplish the runaway stab procedure (the only one that I know of that uses the cutout switches), then they did it incorrectly leaving the aircraft in a grossly out of trim condition. If they were not following a published procedure and merely grasping at straws, then they were grasping at the wrong straw. The immediate remedy to the MCAS inputs was the yoke trim switch, not the trim cutout switch. Once the trim had been neutralized (or at least close), only then would it have been appropriate to disable all electric trim.

Totally agree on direction training is taking, a lot of 'check the tick box' and not a lot of 'what now" novel challenges.
This is likely not helped much by 'binary' simulator data that tend toward prepackaged scenarios and not as much freedom to go in and throw a random combinations of faults into the mix. This is my impression from comments here, I have no first hand knowledge on that.

On the stab trim runway when to hit the cutout switches may have changed along the way, the original 'most likely' trim runaway would be stuck switch/relay which would not be overridden by pilot trim input so focus was on stopping it quickly .
This from a prior post.

Quote:
Originally Posted by tdracer https://www.pprune.org/images/buttons/viewpost.gif (https://www.pprune.org/showthread.php?p=10476677#post10476677)
Posted about this on one of the countless other MAX threads, but it probably bears repeating.
Not too long ago I was at special event at the Museum of Flight - not only was I seated at a table with a bunch of current and retired Alaska Air pilots, during the cocktail hour I ran into a flight test pilot friend who'd been involved in the MAX development (Alaska is an all 737 operator - classics and NGs). To a man, they all agreed that if the stab tirm started doing something you didn't understand or like, the very first thing they'd do is turn it off and trim it manually. Hence the reason Boeing didn't treat MCAS as a flight critical system. However these were all older, high time experienced pilots
That being said, they also all agreed that no sim training for MCAS (or any of the other MAX differences) was a huge miss...

My bolding in above.
One of the criticisms I see of the ET crew is that they did not first trim with electric trim before using cutouts as hinted at in the Lion Air triggered emergency AD.

It is not clear whether lack of manual trim after cutout was due to lack of familiarity with the flip out handles or aero loads or both.
Something had to be happening in the period while electric trim was disabled, we don't know what since the CVR transcript has not been released.

[reamer]

Didn't the ET crew leave it a long time before cutting off the stab trim switches.
So long in fact that the trim was so far out as to make manual trimming impossible.
This is not the procedure recomended. The equivalent of putting in rudder on a V1 cut when the aircraft has rolled on it's back.

[SteinarN]

Didn't the ET crew leave it a long time before cutting off the stab trim switches.
So long in fact that the trim was so far out as to make manual trimming impossible.
This is not the procedure recomended. The equivalent of putting in rudder on a V1 cut when the aircraft has rolled on it's back.

The trim was the following;
9 sec MCAS, followed by
3 sec crew up, followed by
6 sec MCAS, followed by
9 sec crew up, followed by
cutout.

So, the crew put in a total of 12 sec manual trim up, MCAS put in a total of 15 sec trim down. But MCAS trims at about 50% larger speed than manual crew trim, so the end result was significantly out of trim at the time of cut out.
But for all those that say the crew hit cutout without trimming at all, they did in fact trim continuously for 9 sec before hitting cut out. Sadly they didnt trim all the way to zero yoke force. But it is neither stated in any training material that they should do that, it is merely a suggestion that they can do manual trim before cut out. Which they in fact did, for 9 consecutive seconds up until the moment of cutout, which in my opinion is quite a lot of manual trim.

In my opinion the failure here is squarely in Boeings hands as Boeing never in any training material made clear how difficult it is to trim with the trim wheel at such out of trim conditions and never ever made clear how important it is to trim to about zero yoke force before hitting cutout.

[BluSdUp]

I am with You Steinar.
But that would be part of the basic handling of any non-FBW aircraft, and certainly the 737.
Even a issue on a normal go around, some massive trim.

[infrequentflyer789]

Didn't the ET crew leave it a long time before cutting off the stab trim switches.
So long in fact that the trim was so far out as to make manual trimming impossible.
This is not the procedure recomended. The equivalent of putting in rudder on a V1 cut when the aircraft has rolled on it's back.

Depends what you consider a "long time" - from the details we have they appear to have diagnosed a stab trim problem and hit the cutouts within 40sec, which is a lot quicker than I recall in e.g. MentourPilot's demo videos. It's also a lot quicker than the first LionAir crew.

They were actually trimming _up_ when they hit the cutouts - so you are dead wrong there because if they'd left it _longer_ before hitting the cutouts they would have been _less_ out of trim, not more.

Why quit when you are winning? - fear of counter attack maybe. Maybe they thought they were near enough back in trim that they could cutout and do the rest manually and that was better than risking another MCAS. Maybe, just possibly, they'd even practised that in the sim - but the sim, as we now know (and they didn't), wasn't/isn't accurate on the trim wheel forces. We know that some ET pilots were trying to replicate the LionAir scenario in sim from the leaked email from one of them (which, assuming it is not fabricated, is scarily prophetic - "throw in a GPWS PULL UP and it would be a crash for sure").


All this is, of course, just speculation. I would put money on there being something the crew could have done to avoid the crash (because statistically with air accidents that is a winning bet), I am not qualified to say what they should have done, and have no idea what I would have done. However, when we have one crash and lots of people saying "should have done X (fast/first/etc.)" and than another crash after similar failure when they did "do X" followed by people saying "did X too quickly, should have done Y first etc." there is the smell of lots of missing "in hindsight"s in the air (and it doesn't matter whether the field in question is aviation or not). When I see some people saying of the same event "they did X too quick" while others say "they did X too slow", it makes me think this one may not be soluble even with 20/20 hindsight.

[Luc Lion]

It is not clear whether lack of manual trim after cutout was due to lack of familiarity with the flip out handles or aero loads or both.
Something had to be happening in the period while electric trim was disabled, we don't know what since the CVR transcript has not been released.
To this respect, the information transmitted by the interim report is :
At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and FirstOfficer confirmed stab trim cut-out
So, the cutout switches have been switched off between 05:40:35 and 05:40:41,
Then later:
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.
This can only indicate that the crew was unsure if the cutout switches had disabled the electric trim switches or not.
The information about what was the exact function of these switches had not been transmitted to the pilots or assimilated by them.
So they WERE trying to trim up and they discovered that they had neither electric trim nor manual trim available.

There are 2 other points which I noticed in the report and found much informative.
The first point is about uncommanded stabiliser movements:
From 05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units. During this time, aft force was applied to the control columns which remained aft of neutral position.
As this happens during the time the cutout switches were on the off position, I understand that this means that the stabiliser has moved under aerodynamic forces.

The second point is:
At 05:42:10, the Captain asked and the First-Officer requested radar control a vector to return and ATC approved.
At 05:42:30, ATC instructed ET-302 to turn right heading 260 degrees and the First-Officer acknowledged.
At 05:42:43, the selected heading was changed to 262 degrees.
This sequence starts shortly after the FO has reported that manual trim was not working.
The airplane had already started to bank right significantly (between 5° and 15°) at 05:41:30.
When ATC instructed heading 260°, the bank angle is increased gradually from about 10° to 20°.
It is between the 40 seconds that follow the ATC instruction that the crew decided to reset the cutout switches since, at 05:43:10, the DFDR records 2 short electric trim impulses that successfully (but very moderately) moved the stabiliser nose up.
At the time of the short pulses, the bank angle was between 20° and 25°.
When MCAS kicks in 5 seconds after the pulses at 05:43:20, the bank angle increases briefly to 30°.
I understand that the final loss of control happens at a point when the attention of the crew is divided between controlling pitch and another objective (here turning from heading 110° to heading 260°) and that the turn may have played a role in their decision to reset the cutout switches.

Keep in mind that, during all this sequence, the stick shaker is active and the EFS feedback force against aft command is multiplied by 4.

I am not disputing that this crew did not make the best possible decisions.
But apportioning blame is totally useless.
The important stuff for improving the system that led to this situation is understanding how and why these decisions were made.
Apologies for being lengthy.

[yoko1]

The first point is about uncommanded stabiliser movements:

As this happens during the time the cutout switches were on the off position, I understand that this means that the stabiliser has moved under aerodynamic forces.



Could also be the result of attempt at using the manual trim wheel, as it was a relatively small movement. It is also possible that it was an anomaly in the data.



Keep in mind that, during all this sequence, the stick shaker is active and the EFS feedback force against aft command is multiplied by 4.



I think this may be an incorrect understanding. The four times reference comes from the maintenance manual, but our FCOM says the force is doubled. I asked our fleet guys who supposedly asked Boeing and the answer was that the pressure delivered to the elevator feel system is approximately four times (increase from 200 psi to 800 psi) but the force actual felt at the control column is approximately doubled to around 40-50 lbs.

[fdr]

Could also be the result of attempt at using the manual trim wheel, as it was a relatively small movement. It is also possible that it was an anomaly in the data.

DFDR/CVR data won't have an error in a variable like trim position that suddenly happens at that time. A loss of data, that happens, but the engineering values are fixed, so any sensed variable will give an outcome with a constant ac and dc correction/slope and bias. Occasionally the engineering value conversions are incorrect, and the data outcome would be incorrect for all outputs of that variable, that is not the case here. The conversions are post process values... The crew holding very high back pressure against a trim are unlikely to have manually trimmed further forward against their control input, that is not a credible event, so we are left with the possibility that the force on the stab is sufficient to cause creep, and given the design, and IMHO, that should give concern to anyone designing or certifying the plane of that type.

[Fly Aiprt]

I think this may be an incorrect understanding. The four times reference comes from the maintenance manual, but our FCOM says the force is doubled. I asked our fleet guys who supposedly asked Boeing and the answer was that the pressure delivered to the elevator feel system is approximately four times (increase from 200 psi to 800 psi) but the force actual felt at the control column is approximately doubled to around 40-50 lbs.

This is an interesting question.
1) It appears that the manufacturer's document are not clear about the aircraft actual control forces.
2) In any hydraulic actuator/cylinder, the force is proportional to the fluid pressure acting upon the piston part of the actuator.
For the control force to be only doubled when pressure is actually fourfold, a device must be provided that reduces the force from the actuator to the control column.
As the 737 is a mechanical airplane, such a device - if it exists - should also be a hydro-mechanical unit.

Now what would be the point of increasing hydraulic pressure just to reduce its effect on the control system ?

No doubt some Civil Aviation Agency - and maybe even the FAA - will ask that the actual control forces and torque on the trim wheels be measured before drawing any conclusion as to the plausible scenario of the accidents or the 737 return to service.

[Luc Lion]

Could also be the result of attempt at using the manual trim wheel, as it was a relatively small movement. It is also possible that it was an anomaly in the data.
Effectively, when a pilot discovers that he is unable to trim manually his airplane, he may be tempted to try in the opposite direction for checking if the system is mecanically blocked. I read a description of such an action in a PC-6 accident report.
However, in such a case, the trim movement is brief.

The report states and shows in the diagrams that the stabilizer position moved gradually in the AND direction over a period of 2 and half minutes.
This gradual movement can't be imparted as a manual action.
And, as indicated by fdr, an error in DFDR data calibration would produce a constant offset

My best guess is that the brakes on the trim clutch are not totally effective in an extreme out-of-trim situation at high speed.

[MurphyWasRight]

Effectively, when a pilot discovers that he is unable to trim manually his airplane, he may be tempted to try in the opposite direction for checking if the system is mecanically blocked. I read a description of such an action in a PC-6 accident report.
However, in such a case, the trim movement is brief.

The report states and shows in the diagrams that the stabilizer position moved gradually in the AND direction over a period of 2 and half minutes.
This gradual movement can't be imparted as a manual action.
And, as indicated by fdr, an error in DFDR data calibration would produce a constant offset

My best guess is that the brakes on the trim clutch are not totally effective in an extreme out-of-trim situation at high speed.

The FDR traces are coarse so it is hard to know for sure whether the changes were truly continuous or a series of small steps, the raw data should show which.
Other possibilities, of course could also be 'all of the above'

1: Each (ineffective) manual trim attempt briefly unlocked the brakes allowing an aero load induced movement.
I have no knowledge on the mechanical interaction between manual trim and the brakes so this may not be possible.

2: The pilots went back a bit before attempting to go forward, this can be seen in the mentour video demonstration almost like they were bouncing backwards.
The cables do act as a spring so hard to say if this was enough to actually move the stab.

[yoko1]

This is an interesting question.
1) It appears that the manufacturer's document are not clear about the aircraft actual control forces.
2) In any hydraulic actuator/cylinder, the force is proportional to the fluid pressure acting upon the piston part of the actuator.
For the control force to be only doubled when pressure is actually fourfold, a device must be provided that reduces the force from the actuator to the control column.
As the 737 is a mechanical airplane, such a device - if it exists - should also be a hydro-mechanical unit.

Now what would be the point of increasing hydraulic pressure just to reduce its effect on the control system ?

No doubt some Civil Aviation Agency - and maybe even the FAA - will ask that the actual control forces and torque on the trim wheels be measured before drawing any conclusion as to the plausible scenario of the accidents or the 737 return to service.

I agree that there is conflicting information in the tech manuals, and I've asked our fleet managers to seek a correction. That being said, it is entirely possible that the force reduction is simply a consequence of the mechanical linkages (i.e. levers, gear or pulley reduction, etc) built into the system and is thus transparent to the pilots. I have been told that the pull force required on the control column should never exceed 50 lbs. Hopefully the accident investigation boards will include this issue in their investigations.