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The Ethiopian Airlines pilots followed the EAD to the letter. First, they attempted to adjust trim using electric stabilizer trim, and then upon realizing that

by ummonk 5y ago

The Ethiopian Airlines pilots followed the EAD to the letter. First, they attempted to adjust trim using electric stabilizer trim, and then upon realizing that the they were experiencing an uncommanded nose down stabilizer trim, they followed the runaway stabilizer procedure - namely, stab trim cutout and trim wheel grasp and hold. Afterwards, they attempted to adjust the stabilizer manually. There is a note in the EAD that electric stabilizer trim can be used to neutralize the stabilizers before doing a stab trim cutout, but crucially Boeing did not instruct pilots to make sure to neutralize trim first using electric trim before doing the stab trim cutout.

WalterBright 5y ago
> Boeing did not instruct pilots to make sure to neutralize trim first using electric trim before doing the stab trim cutout. Yes, they did: "Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT." https://theaircurrent.com/wp-content/uploads/2018/11/B737-MAX-AD-1107.pdf https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA... Note also that the EA pilots had already successfully overridden and restored normal trim twice with the electric trim switches. (I added the emphasis on "before".)
- ummonk 5y ago
  That's not an instruction - it's a digression. The wording there is "can be used". The actual instruction is to follow the AFM Runaway Stabilizer procedure. That's exactly what the Ethiopian Airlines pilots did.
  - WalterBright 5y ago
    > That's not an instruction - it's a digression. The wording there is "can be used". Why do you think Boeing wrote an EMERGENCY AIRWORTHINESS DIRECTIVE and the FAA mandated it be sent to all MAX pilots? If you're a pilot, it is YOUR JOB to read, understand, and remember every EMERGENCY AIRWORTHINESS DIRECTIVE. Not to parse words. If you want to parse words, get a job as a lawyer, not a pilot. The "can be used" is there to explain how to overcome aerodynamic forces that make using the manual trim wheel difficult.
    - atdrummond 5y ago
      Please don’t flag replies like this; thankfully I was able to vouch for Walt. For some background, Walt and I are routinely brigaded with downvotes on 737 MAX threads. What he and I have in common, compared to those who engage in such behaviors, is that unlike those we typically are replying to, we both have extensive backgrounds in the aviation field, especially on the programming side. Back on topic, the takeaway that Walt is making and that seems to be missed continually in these threads, is that Lion Air did not lose their plane due to the MAX’s MCAS implementation. Rather, the pilots engaged with the plane in a manner precisely opposite to what procedure calls for. Despite all of the poor calls made by Boeing here, if LA’s pilots had simply reacted as the previous flight’s pilots had, the plane would have made it.
      - ummonk 5y ago
        Why are you bringing up Lion Air pilots when the discussion is about the Ethiopian Airlines flight?
        WalterBright 5y ago
        The first LA crew was not aware of the existence of MCAS, nor did they have the benefit of the Emergency Airworthiness Directive. But they worked the problem and solved it and landed safely.
      - WalterBright 5y ago
        A clarification - my computing experience at Boeing was writing Fortran programs to solve design problems, not aviation software. However, at Boeing I spent 3 years working on the stabilizer trim gearbox on the 757. The 757 system is a newer design than the 737, in that it uses a dual drive system connected via a differential gear system rather than having the manual wheels in the cockpit. Nevertheless, the difference is in detail, not concept. Both systems have cutoff switches within easy reach of the pilot, for a damn good reason - to stop uncontrolled stabilizer trim action. While the 757 did not have MCAS, it did have a computer autopilot that could move the stabilizer. I did some searching online of the MAX trim system, and indeed the electric trim switches override MCAS commands. In all three incidents the pilots did override it and return the trim to normal. In the first incident, after a couple times, the crew trimmed it to normal and then cutoff the stab trim. Continued the flight and landed without further incident. In the second, the pilots brought it back to normal 25 times before the final plunge. For whatever reason, they never switched off the trim system. I haven't got a solid reference to the EA one, but it appears they restored trim twice before the final plunge. They then turned off the trim system in the plunge. They could not turn the manual trim wheels due to the aerodynamic forces. So they turned the trim back on, the MCAS came on again making things worse. Why they did not counter again with the electric trim I do not know. Why they did not turn off the trim when it was in the normal position I do not know. Those are excellent questions for the NTSB to answer. But what they didn't do was follow the directions in the EAD.
whoknowswhat11 5y ago
Is this a joke? ERROR: Literally the first paragraph of the EAD is about controlling airspeed. [Edit: This is not correct] They hit 700(!!) MPH. They literally commanded full take off power to accelerate the plane into the ground. You can add power if your pitch is high to arrest a sink rate (ie, during landing), but if you are pitched down, you pull power. There is also a 300 second limit on T/O power - I'd be interested if they exceeded that as well. The maintenance on this plane was terrible. This was not a situation where folks involved "did everything right". For those not familiar, approx 3 minutes after they did a stab trim cutout they put stab trim back to normal. That's never been in any guidance for EAD or runaway. The 4th activation of MCAS moved trim down (to 1 unit, should have probably been at 4.3 - 5.x or so). That probably doomed them.
- ummonk 5y ago
  The first paragraph of the EAD is: "Disengage autopilot and control airplane pitch attitude with control column and main electric trim as required. If relaxing the column causes the trim to move, set stabilizer trim switches to CUTOUT. If runaway continues, hold the stabilizer trim wheel against rotation and trim the airplane manually."
  - WalterBright 5y ago
    The entire EAD must be read, not the first paragraph. Including the digressions (your phrase). It's only two pages. I am not a pilot. But I am an aerospace engineer who worked on critical flight detail designs. You've likely flown on my work. My father was a pilot for the AF for 20 years. You don't get to be an old pilot if you don't pay attention 100% to the instructions and training. Flying isn't like driving a car. Humans are not natural flyers. You rarely get a second chance if you make a mistake flying. Maybe 90% of flight training is dealing with emergencies. If you're not dedicated to doing it right, and doing it 100%, every time, you've got no business being a pilot with hundreds of lives depending on you. P.S. I've gone flying with pilot friends many times. I watch them do the preflight. If they're not 100% perfect with it, I'm getting off.
    - 5y ago

by ummonk 5y ago

WalterBright 5y ago

> Boeing did not instruct pilots to make sure to neutralize trim first using electric trim before doing the stab trim cutout. Yes, they did: "Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT." https://theaircurrent.com/wp-content/uploads/2018/11/B737-MAX-AD-1107.pdf https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA... Note also that the EA pilots had already successfully overridden and restored normal trim twice with the electric trim switches. (I added the emphasis on "before".)

ummonk 5y ago
That's not an instruction - it's a digression. The wording there is "can be used". The actual instruction is to follow the AFM Runaway Stabilizer procedure. That's exactly what the Ethiopian Airlines pilots did.
- WalterBright 5y ago
  > That's not an instruction - it's a digression. The wording there is "can be used". Why do you think Boeing wrote an EMERGENCY AIRWORTHINESS DIRECTIVE and the FAA mandated it be sent to all MAX pilots? If you're a pilot, it is YOUR JOB to read, understand, and remember every EMERGENCY AIRWORTHINESS DIRECTIVE. Not to parse words. If you want to parse words, get a job as a lawyer, not a pilot. The "can be used" is there to explain how to overcome aerodynamic forces that make using the manual trim wheel difficult.
  - atdrummond 5y ago
    Please don’t flag replies like this; thankfully I was able to vouch for Walt. For some background, Walt and I are routinely brigaded with downvotes on 737 MAX threads. What he and I have in common, compared to those who engage in such behaviors, is that unlike those we typically are replying to, we both have extensive backgrounds in the aviation field, especially on the programming side. Back on topic, the takeaway that Walt is making and that seems to be missed continually in these threads, is that Lion Air did not lose their plane due to the MAX’s MCAS implementation. Rather, the pilots engaged with the plane in a manner precisely opposite to what procedure calls for. Despite all of the poor calls made by Boeing here, if LA’s pilots had simply reacted as the previous flight’s pilots had, the plane would have made it.
    - ummonk 5y ago
      Why are you bringing up Lion Air pilots when the discussion is about the Ethiopian Airlines flight?
      - WalterBright 5y ago
        The first LA crew was not aware of the existence of MCAS, nor did they have the benefit of the Emergency Airworthiness Directive. But they worked the problem and solved it and landed safely.
    - WalterBright 5y ago
      A clarification - my computing experience at Boeing was writing Fortran programs to solve design problems, not aviation software. However, at Boeing I spent 3 years working on the stabilizer trim gearbox on the 757. The 757 system is a newer design than the 737, in that it uses a dual drive system connected via a differential gear system rather than having the manual wheels in the cockpit. Nevertheless, the difference is in detail, not concept. Both systems have cutoff switches within easy reach of the pilot, for a damn good reason - to stop uncontrolled stabilizer trim action. While the 757 did not have MCAS, it did have a computer autopilot that could move the stabilizer. I did some searching online of the MAX trim system, and indeed the electric trim switches override MCAS commands. In all three incidents the pilots did override it and return the trim to normal. In the first incident, after a couple times, the crew trimmed it to normal and then cutoff the stab trim. Continued the flight and landed without further incident. In the second, the pilots brought it back to normal 25 times before the final plunge. For whatever reason, they never switched off the trim system. I haven't got a solid reference to the EA one, but it appears they restored trim twice before the final plunge. They then turned off the trim system in the plunge. They could not turn the manual trim wheels due to the aerodynamic forces. So they turned the trim back on, the MCAS came on again making things worse. Why they did not counter again with the electric trim I do not know. Why they did not turn off the trim when it was in the normal position I do not know. Those are excellent questions for the NTSB to answer. But what they didn't do was follow the directions in the EAD.

whoknowswhat11 5y ago

Is this a joke? ERROR: Literally the first paragraph of the EAD is about controlling airspeed. [Edit: This is not correct] They hit 700(!!) MPH. They literally commanded full take off power to accelerate the plane into the ground. You can add power if your pitch is high to arrest a sink rate (ie, during landing), but if you are pitched down, you pull power. There is also a 300 second limit on T/O power - I'd be interested if they exceeded that as well. The maintenance on this plane was terrible. This was not a situation where folks involved "did everything right". For those not familiar, approx 3 minutes after they did a stab trim cutout they put stab trim back to normal. That's never been in any guidance for EAD or runaway. The 4th activation of MCAS moved trim down (to 1 unit, should have probably been at 4.3 - 5.x or so). That probably doomed them.

ummonk 5y ago
The first paragraph of the EAD is: "Disengage autopilot and control airplane pitch attitude with control column and main electric trim as required. If relaxing the column causes the trim to move, set stabilizer trim switches to CUTOUT. If runaway continues, hold the stabilizer trim wheel against rotation and trim the airplane manually."
- WalterBright 5y ago
  The entire EAD must be read, not the first paragraph. Including the digressions (your phrase). It's only two pages. I am not a pilot. But I am an aerospace engineer who worked on critical flight detail designs. You've likely flown on my work. My father was a pilot for the AF for 20 years. You don't get to be an old pilot if you don't pay attention 100% to the instructions and training. Flying isn't like driving a car. Humans are not natural flyers. You rarely get a second chance if you make a mistake flying. Maybe 90% of flight training is dealing with emergencies. If you're not dedicated to doing it right, and doing it 100%, every time, you've got no business being a pilot with hundreds of lives depending on you. P.S. I've gone flying with pilot friends many times. I watch them do the preflight. If they're not 100% perfect with it, I'm getting off.
  - 5y ago