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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 5th Apr 2019, 05:52
  #3241 (permalink)  
 
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At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough.

At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,4002 ft, two momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in the ANU direction from 2.1 units to 2.3 units.
This bit baffles me. Apart from the question of why didn't they get the aircraft back in trim earlier, at this point in time the situation looked just salvageable.

Presumably somewhere in-between these two time-stamps, the stab trim cutout switches were turned back on.

There is no mention of any cockpit discussion taking place from the CVR about turning them back on, so perhaps the Captain just reached down and reactivated the stab trim in desperation.

But why only two short blips of trim? They worked! It is stated the trim moved from 2.1 to 2.3 units. Re-engaging the stab trim was working! So why stop there? If only they'd trimmed it back to around 5 units and then hit the cutout switches again it would have become a manageable problem again. Surely every Max pilot in the world would have briefed themselves on this after Lion Air?

This makes the event seem all the more tragic - so close to solving the problem.
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Old 5th Apr 2019, 06:22
  #3242 (permalink)  
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With respect to Why didn't they use the yoke trim switches effectively?
How much or how little, rather, hand flying experience did they have?
Captain was cadet from the start at ET, operated from the get go in an "AP on at 200' and off at 1000'/500' " SOP environment, and the FO was brand new in just such an environment. Unfamiliar with using trim switches whilst flying .. unfamiliar with hand flying, and having to do it with the stick shaker on max continuous with unreliable airspeeds. Ouch
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Old 5th Apr 2019, 06:36
  #3243 (permalink)  
 
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Originally Posted by BluSdUp View Post
And here comes the problem: In 26 Okt 2017 he made Cpt 737-800 , SO less then 1.5 years Command.
There is a total of 1477hrs 738 and 103hrs Max.
Of which a lot is FO time!!
So, a low timer indeed!

This is a warning on so many levels!
Someone who's flown 8000 hours from 2011 to 2019 can hardly be called a "low-timer", that's more than most people flying in Europe (or even the US would rack up in that time).
Most Commanders flew as FOs before (and the saying goes that those who didn't aren't the best to fly with). Every time there's a new type out there, someone's gonna have to start flying it with zero hours on this type.
Where would you procure "ready-made" commanders with experience and command time on type?

If I got you wrong, please elaborate.
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Old 5th Apr 2019, 06:38
  #3244 (permalink)  
 
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Elec trim about 230 knots impossible?

EASA document from Feb 2016 allegedly states that electric trim would not work above 230 knots. That might explain why they re-engaged trim (if the indication that they did re-engage trim is correct)...

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

It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s center console rather than an electric thumb switch on the control yoke.
https://www.reuters.com/article/us-e...-idUSKCN1RA0DP
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Old 5th Apr 2019, 06:46
  #3245 (permalink)  
 
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Originally Posted by NSEU View Post
The Maintenance Manual has upper and lower limits when there are no airloads:

The torque required to turn the wheel is somewhere between 22 and 62pound-inches (2.5 and 7 newton-meters).

What's the radius of the trim wheel at the handle position?
I would say the radius at the handle is between 10 and 15cm. So, that would give a force required to manually crank - WITHOUT any air loads - of 2,5 to 7 kg for a 10 cm radius and 1,67 to 4,67 kg for a 15 cm radius wheel.
I am fairly sure that the radius at the handle is closer to 10 cm than to 15 cm.
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Old 5th Apr 2019, 06:59
  #3246 (permalink)  
 
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Trim Runaway C/L

C/L is actually trying to do the troubleshooting - first step is to eliminate autopilot false inputs and then if that does not help - trim motor switches go to cut-out.
Should it be the other way around - trim motor switches to cut out first and then troubleshoot if you want.

Especially after the Lion crash when it was widely known that disengaging the autopilot is a pre-condition for erroneous MCAS trim input.
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Old 5th Apr 2019, 07:02
  #3247 (permalink)  
 
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MCAS fired a blank

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

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

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

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

Last edited by SLFstu; 5th Apr 2019 at 07:09. Reason: fixed formatting of special characters
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Old 5th Apr 2019, 07:02
  #3248 (permalink)  
 
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Is it not a bit quaint that a 21st century airline manufacturer still believes that a hand-cranked pulley is the best final solution to a complex systems problem?

Surely the biggest lesson to learn from this event is that the Max should be the last of the 737 family? (No disrespect to the 737 which has been an outstanding aircraft......... but is rather long in the tooth).

Interesting fact. The 737 first flew about 50 years ago and, to date, there have been about 11000 manufactured and 4000 on order. The A320 range first flew 30 years ago and there have been about 8500 built and 6000 on order. Sort of explains why Boeing need to stay in the game.
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Old 5th Apr 2019, 07:04
  #3249 (permalink)  
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Originally Posted by Rananim View Post
units but FO couldnt get the manual trim working.FO has 200 hours
so this is not surprising
I'm sorry but how many hours does one require before one can turn a wheel?
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Old 5th Apr 2019, 07:23
  #3250 (permalink)  
 
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Turning the wheel was on my type rating course, but featured only one other time in my run of recurrent sims. I would guess that the low houred FO probably had the best recency on a bit of wheel turning.
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Old 5th Apr 2019, 07:24
  #3251 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
I'm sorry but how many hours does one require before one can turn a wheel?
more than 200. There’s a diff between competence and proficiency.

theres a video of a pair of idiots on YouTube who run through a runaway trim procedure. The ‘fo’ cranks the wheel like he’s rolling a drum - meanwhile, the extendable handle sat comfortably in its retracted position.
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Old 5th Apr 2019, 07:33
  #3252 (permalink)  
 
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Originally Posted by Cows getting bigger View Post
Is it not a bit quaint that a 21st century airline manufacturer still believes that a hand-cranked pulley is the best final solution to a complex systems problem?
It is unfortunate, that following the lion-air crash, Boeing and the FAA detailed an AD, that to address a faulty MCAS system, required pilots to disable a perfectly working electric trim system. For a pilot that happened to be appropriately trimmed already, high and not too fast, trimming by the trim wheels is going to be OK. For pilots in more challenging situations, then this was going to be a problem. Both Boeing and the FAA would have been aware of this.

Once the faulty MCAS design had been recognized, it should have been fixed or at the very least, a mechanism introduced and documented, so that a pilot could disable the errant MCAS system without taking out other, important, working systems.
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Old 5th Apr 2019, 07:38
  #3253 (permalink)  
 
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I think there is a reasonable consensus (lest's say 50% chances) that vane shaft broke, keeping AOA vane attached or not, and subsequent alarms and checklists (both useful and useless) threw the crew out of balance. They didn't manage airspeed and lost ability to trim. They reengaged electric trim, was not strong enough either, forgot to CUTOUT, mcas trimmed down, EOF.

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

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

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

Even if you don't do it:

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

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

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

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

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

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


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

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Old 5th Apr 2019, 07:39
  #3254 (permalink)  
 
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Bjørn Fehrm at Leeham:
Bjorn’s Corner: ET302 crash report, the first analysis

At 7 the aircraft nose is dipping (see Pitch Attitude Disp trace) because PF can no longer hold against the Yoke forces we discussed Wednesday (Ctrl Column Pos L/R). PF decides he needs Electric Trim to stop the aircraft from diving. Cut Off switches are put to Electric Trim active. PF successfully trimmed against the last MCAS attack, he can do it again.

The insufficient trim mystery after re-activation of Electric Trim

After 7 PF commands Electric Trim Nose Up in two short cycles. I asked my selves (as did others) why these short trims? They are fighting to get the nose up to the extent they risk switching in the Electric Trim again. Then why not trim nose up continuously or for at least long cycles once Electric Trim is there? It took me several hours to find an explanation. Here my take:

To understand the blip trims one must have flown fast jets at low altitude. At the speed ET302 is flying, 360kts, it’s hypersensitive to trim. The least trim action and the aircraft reacts violently. Any trimming is in short blips.

As PF holds the nose up with a very high stick force, now for a long time, his sensitivity to release stick with trim is not there (this is what Pilots do when they trim nose up, otherwise the aircraft pitches up fast). He trims therefore in short blips and has difficulty to judge the trim effect he has achieved. His is not flying on feel. He can’t, he is severely out of trim, holding on to the Yoke with a strong pull force.

Anyone who has flown a grossly out of trim aircraft at high speeds knows your feel is compromised. The sensors you have to rely on are your eyes, not your hands.

PF has the horizon glued to read the aircraft. The result is the short nose-up trims we see. The nose goes up and the stick force needed is reduced. His judgment is; this is enough for now. Any MCAS attack I now trim against, then I correct my trim if I need to.

But the aggressive MCAS, trimming with a speed 50% higher than the pilot and for a full nine seconds, kicks in at 8 with a force they didn’t expect. Speed is now at 375kts and MCAS was never designed to trim at these Speed/Altitude combinations. Dynamic pressures, which governs how the aircraft reacts to control surface movements, is now almost double it was when last MCAS trimmed (Dynamic pressure increases with Speed squared).

The Pilots are thrown off their seats, hitting the cockpit roof. Look at the Pitch Attitude Disp trace and the Accel Vert trace. These are on the way to Zero G and we can see how PF loses stick pull in the process (Ctrl Column Pos L). He can barely hold on to the Yoke, let alone pull or trim against.

His reduced pull increases the pitch down further, which increases the speed even more. At 05.45.30 the Pilots have hit the seats again (Accel Vert trace and Ctrl Columns force trace) and can start pulling in a desperate last move. But it’s too late. Despite them creating the largest Control Column movement ever, pitch down attitude is only marginally affected.

We have Control Column displacement this time, JT610 was Force. If the elevator reacts to these displacements, at the Dynamic Pressure we have, we should have seen the diving stop. The lack of reaction to the large Control Column displacement of two Pilots pulling makes me think we now have blowback. This is not a design fault, we are well beyond Vmo. But it explains the rapid dive, unhindered by the Pilots’ actions.

It’s easy to say “Why didn’t they trim then?”. Because they are going down at 20 degrees nose down (which is a lot, a normal landing approach is 3°) and at 400kts. Then you just pull for all you have. And the aircraft is not reacting to the largest Control Column displacement since takeoff. This makes them pull even harder, the aircraft is unresponsive and they are fighting for theirs and all the passenger lives.

A final reflection: Once again we have been given no elevator trace. Why? It’s there, why can’t we see it. It would have given us a better understanding of what’s happening in the last part of the flight.
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Old 5th Apr 2019, 07:42
  #3255 (permalink)  
 
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Reading the report fills me with horror. Two of them, fighting to find the solution, with decreasing success as they are overloaded.

There is too much conflicting information to guarantee that a crew resolves the problem.
  • The aircraft is stalling, yet the pitch/thrust/speed appear correct.
  • As thrust is applied, the stall condition gets "worse", as you have to apply more back pressure to maintain the pitch.
  • The two primary airspeeds are different.
  • The stick shaker is activated, yet the airspeed is high.
  • The airspeed is high, yet the aircraft pitches down as it speeds up, not up.
  • As you speed up, you normally trim down. But it feels like I should trim up.

Stuff that I have never did in the 737 sim:
  1. Found myself with a stab trim that overpowered elevator at max deflection.
  2. The yo-yo or rollercoaster manual trim exercise.

Finally, it needs to be remembered that the deafening stick shaker reduces cognitive ability, and is shaking both control columns, and may therefore be prominent as the "primary" problem.
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Old 5th Apr 2019, 07:53
  #3256 (permalink)  
 
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I've read and imagined the "hipersensitive trim" theory for short blips before the final dive.

I think it is plausible. I think not enough electric trim force is plausible also.

All we need to know the truth is a zoomed in view of the trim units around that time.

I guess it doesn't make any difference, though.
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Old 5th Apr 2019, 07:54
  #3257 (permalink)  
 
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Originally Posted by ecto1 View Post
I think there is a reasonable consensus (lest's say 50% chances) that vane shaft broke, keeping AOA vane attached or not, and subsequent alarms and checklists (both useful and useless) threw the crew out of balance. They didn't manage airspeed and lost ability to trim. They reengaged electric trim, was not strong enough either, forgot to CUTOUT, mcas trimmed down, EOF.

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

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

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

Even if you don't do it:

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

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

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

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

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

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


Chances are that the very same secuence of events, without MCAS final strike, has happened more than once before in other 737 variants (AOA fails, unreliable air data, stick shaker, big confusion, lack of proper aviation and or navigation and possibly all the way to overspeed and uneffective trim). Only without MCAS the aircraft would have been more or less in trim and therefore not nosediving and making the news.
Fully agreed. There could be much more on the list (e.g. same sound for cabin pressure altitude warning and t/o config, which killed 121 people)
Sensors will continue to break in future. Bits will continue to flip. Wires will continue to fail. Connectors will continue to corrode. People will continue to be humans.
It is the damned duty of every OEM lead design and certification engineer and every FAA, EASA and have you representative to think of possible failure modes and ask for solid and sane design.
It is not the duty to think about saving money by keeping a 40 years old certification in place. Which lets the boss, the boss of the boss and the boss of the boss of the boss smile.
It seems basic airmen and engineering knowledge is lost in the industry and substituted by plain software commodity engineering skills, that are typical for games, desktop software and iOS apps. These do not run airplanes.
Not the only thing that is lost in this world.
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Old 5th Apr 2019, 07:54
  #3258 (permalink)  
 
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What moment does one get from deploying speed brakes ? NU or ND ?

(One of the aircraft I have flown had a partial speed brake deployment with elevator stuck in a ND setting in the C/L....)
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Old 5th Apr 2019, 07:55
  #3259 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
I'm sorry but how many hours does one require before one can turn a wheel?
Chesty, we discussed this earlier, and you said you have flown the 737 with manual trim and it was no problem.
I’ve only tried this a few times, but found the manual trim to be pretty hard. A friend of mine got «Stab out of trim» enroute and diverted because he thought he had a jammed stab. This after he tried manual trim and found it so hard he concluded he had a jammed stab.
It now looks like manual trim is nearly impossible at higher speeds.
It puzzels me a bit that the stab can be trimmed so far it will bring the aircraft out of the pilot’s control. And then you can’t manually bring it back under control because the trim forces are too high.

How Boeing will solve this is beyond me. MCAS is a killer and if they restrict it it will affect the certification. In order to get rid of MCAS they have to redesign the aircraft.
IMHO the MAX will stay on ground for a long time.
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Old 5th Apr 2019, 08:04
  #3260 (permalink)  
 
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Originally Posted by NiclasB View Post
EASA document from Feb 2016 allegedly states that electric trim would not work above 230 knots. That might explain why they re-engaged trim (if the indication that they did re-engage trim is correct)...
Might be a good time to reiterate the relevant part from the document:

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