8 ms·

Will be interesting to see the details when the report is actually public. It does sound like the scenario that Mentourpilot explored in the simulator is close

Will be interesting to see the details when the report is actually public. It does sound like the scenario that Mentourpilot explored in the simulator is close to what happened, namely: Bad AoA probe causes MCAS to trim down, and also to indicate IAS disagree. Pilots increase throttle as per non-normal checklist to reduce the risk of stalling due to unreliable airspeed. Pilots disable electric stabilizer trim, as per Boeing's advice, without trimming back to neutral trim. Plane is now low, accelerating, and trimmed nose down. Pilots likely started to trim up with the manual trim wheels, but that's very slow, and gets harder as airspeed increases. And you don't want to reduce power, because that will cause a pitch-down, and you're close to the ground. At this point you've run out of options that are recommended by Boeing. The only remaining option is to re-enable electric stabilizer trim, and use that to trim nose-up. Now, from what I understand, appying nose-up electric trim should override MCAS, and so this course of action should be possible. However, at this point, you're basically a test pilot - this is not on any of Boeing's checklists or training. Why didn't it work? We'll have to wait for the full report for that I think.

lysp 8y ago
Does anyone have a mirror of that video?
- mhandley 8y ago
  This was posted on PPrune: "Originally Posted by infrequentflyer789 Since this video may not be coming back I'll post a sort of transcript from memory since I was lucky enough to get to watch it. I'll try and just describe what I saw and keep my commentary/speculation to a minimum - in <italic>. Bear in mind this is a non-pilot observer's take on it from flaky memory: There is a fair bit of intro talk then the sim. They are in NG sim, not MAX, no surprise there. Mentour in left seat. They start at low altitude, I think it was commented on, not at takeoff, I can't remember if they showed putting flaps up or started with flaps up and said it was just after flaps up. No stick shaker, that I saw. <presume means no elevator feel shift either, and that actual AOA error is not being simulated> IAS disagree then simulated - or they just did the memory items, I didn't notice warning light (not that I would) and he didn't note it, there was an aural alarm but I think that was for AP disconnect <I don't think this is exactly what the accident flights faced, they had shaker and IAS disagree from takeoff> IAS disagree memory items, AP/AT OFF, FDs OFF, 75% N1, 4degrees Throttles are pushed forward to get 75%, he comments that at low alt with denser air this is a lot of thrust and hence speed will increase Trim runs, obviously sim doesn't have MCAS so not sure if they are simulating runaway or if he is doing it with the column switches Comment is made that he was _expecting_ trim to run, because speed is changing, he says it will take a couple of cycles of fighting it with the switches before being definite that it is wrong They discuss (he raises) that he is having flight control issue, they conclude it is trim that is the problem, they now run the stab trim runaway memory items finishing by hitting the switches. At this point he is clearly holding quite a bit of pressure on the column, but not obviously losing control of pitch Now he points out that trim has only got down to (I think) 3 degrees on the indicator (zero being full nose down, I think) and that they are now going to "try something" - video captions say "don't try this at home", like we've all got a FFS in our shed or a 737 on the drive :-) At this point the guy in the right seat uses the handle to wind the trim further _forward_. He stops when he clearly cannot wind it further - but they point out that it's still not at full nose down Mentour is obviously struggling to keep the nose up at this point. I noticed he didn't seem to have the shoulder straps on (right seat did), possibly because he was frequently turning round to talk to the camera. That probably didn't help, but on the other hand he didn't have stick shaker or feel shift to cope with either. Now, with Mentour pulling back, the right seat guy tries to wind the trim back with the handle - and he struggles to move it at all They stop the sim, I think it was after stopping that he noted that at that point they were at 310 (maybe he said 340) knots. I think there was then some further commentary, at one point I think he mentioned the rollercoaster to unload the stab and allow trimming, but commented that close to the ground the instinct is to pull back - I may be imagining that or remembering it from another video though. And that was about it. I can try to answer questions on the video if anyone has any. The eye-opener for me wasn't the force on the control column (which was held anyway), it was that the trim couldn't be moved, in either direction. From somewhere I had got the impression that those wheels had a lot of leverage, due to the gearing, which was why a lot of turns would be required, but it seems that a lot of turns would be required and a gorilla to make them..."
  - CamperBob2 8y ago
    Since this video may not be coming back I'll post a sort of transcript from memory since I was lucky enough to get to watch it. I'll try and just describe what I saw and keep my commentary/speculation to a minimum - in <italic>. Bear in mind this is a non-pilot observer's take on it from flaky memory Was the video pulled? Who did that, and why?
    - mhandley 8y ago
      The speculation is that his employer, which flies a lot of 737s, didn't like him using a company simulator to illustrate a safety issue with the 737.
    - colde 8y ago
      He pulled it himself. https://twitter.com/MenTourPilot/status/1113723580284583936 https://twitter.com/MenTourPilot/status/1113723580284583936
      - jillesvangurp 8y ago
        His channel is worth following. He often posts insightful stuff related to incidents with 737s or just general information. He had a nice video about emergency procedures with a total engine failure in (probably) the same simulator just a few weeks ago.
  - TheSpiceIsLife 8y ago
    Is anybody here capable of calculating the force required to move the trim tabs on a 737MAX at 310 knots at low altitude? I imagine at that speed there would be quite some force on the elevator and trim tabs.
    - mhandley 8y ago
      There's no trim tab on a 737 - the whole horizontal stabilizer is moved to trim the aircraft in pitch. Normally this is done electrically, but the stabilizer jackscrew can also be moved using manual trimwheels that move the jackscrew using physical cables. Whether this is possible at high airspeed while the stabilizer is trimmed nose down, and the elevator is being pulled up as hard as you can to avoid diving - that's the question that is being raised. Edit: this shows the jackscrew in operation: https://www.youtube.com/watch?v=rxPa9A-k2xY https://www.youtube.com/watch?v=rxPa9A-k2xY
- sundvor 8y ago
  Not that video, but at least it shows the automatic trim system in action - and is rather educational: https://youtu.be/l62NvkRWa5E https://youtu.be/l62NvkRWa5E . Even better: https://youtu.be/xixM_cwSLcQ https://youtu.be/xixM_cwSLcQ
VBprogrammer 8y ago
The official report will make for interesting reading. The speculation over the last few days is starting to fill in some questions I've had: - Why didn't the pilots identify the issue as MCAS malfunction and follow the guidence? They did and it didn't work for some reason. Possibly because of the air loads on the stabilizer. - Why did the AoA sensor on a new aircraft fail? Suspected bird strike.
- woofcat 8y ago
  - They did and it didn't work for some reason. Possibly because of the air loads on the stabilizer. Has the CVR transcript been released? I can't find any source on the procedures taken in the cockpit prior to the crash.
  - VBprogrammer 8y ago
    I believe the media have been briefed on the the contents of the report but it isn't yet publicly available. It's annoying because I don't trust the media to get the details correct on this type of thing.
- peteradio 8y ago
  Why is nobody looking at the manufacturer of the sensor?
  - VBprogrammer 8y ago
    If someone connected a big industrial stop switch to a solenoid and pointed that solenoid at the trigger of a rifle aimed at the person pressing the button I don't think you would expect anyone to look particularly hard at the person who manufactured the switch. If it was indeed a bird strike which took out the sensor then they seem to be completely beyond all possible blame. Even if it wasn't I'm sure they could point at a host of documentation regarding the usual MTBF of their sensors and why this application was inappropriate.
    - peteradio 8y ago
qaq 8y ago
Why speculate here's memory item (pilot should know without looking at the manual) for all 737s for runaway stabilizer. Do you have any information they followed this. All published information we had was specifically that they did not follow the procedure: CONTROL COLUMN - HOLD FIRMLY AUTOPILOT (if engaged) - DISENGAGE Do not re-engage the autopilot. Control airplane pitch attitude manually with control column and main electric trim as needed If the Runaway Continues STAB TRIM CUTOUT SWITCHES (both) - CUTOUT If the Runaway Continues STABILIZER TRIM WHEEL - GRASP and HOLD
- mhandley 8y ago
  From today's Ethiopian Airlines press release: "The preliminary report clearly showed that the Ethiopian Airlines Pilots who were commanding FlightET 302/10 March have followed the Boeing recommended and FAA approved emergency procedures to handle the most difficult emergency situation created on the airplane. Despite their hard work and full compliance with the emergency procedures, it was very unfortunate that they could not recover the airplane from the persistence of nose diving. As the investigation continues with more detailed analysis, as usual we will continue with our full cooperation with the investigation team." Edit: perhaps you're refering to the LionAir crash, where they didn't disable stabilzer trim?
  - qaq 8y ago
    Thats a press release there is cockpit audio pilots vocalize actions when they take them the cutout switches were never turned off. Would you point to the part of the actual report that says the position of cutout switches was off?
    - mhandley 8y ago
      The preliminary report is not yet public - Ethiopian have seen it, hence their press release, and some of the media have been briefed on its contents, hence the BBC article, but it's not yet public.
      - 8y ago
dingaling 8y ago
A bad AoA probe wouldn't trigger IAS disagreement alert ( that is fed from the separate pitot tubes ) but could activate the corresponding stick-shaker which may make the pilots consider the possibility of IAS uncertainty. Just a minor quibble. Also increasing airspeed isn't a panacea for avoiding a stall, it is entirely possible to enter a high-speed stall if the AoA isn't managed. And in fact as mentioned speed can make recovery more difficult due to airloads on non-FBW aircaft.
- VBprogrammer 8y ago
  From the AD issued after the Lion Air accident: Additionally, pilots are reminded that an erroneous AoA can cause some or all of the following indications and effects: - Continuous or intermittent stick shaker on the affected side only. - Minimum speed bar (red and black) on the affected side only. - Inability to engage autopilot. - Automatic disengagement of autopilot - IAS DISAGREE alert. - ALT DISAGREE alter. - AOA DISAGREE alert (if the AOA indication option is installed) - FEEL DIFF PRESS light
  - dingaling 8y ago
    Thank you for the corrections!
- mhandley 8y ago
  The bad AoA probe can cause IAS disagree, according to the FAA Emergency Airworthyness Directive: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/83ec7f95f3e5bfbd8625833e0070a070/$FILE/2018-23-51_Emergency.pdf http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/... Take a look at the graphs from the LionAir crash: http://nrg.cs.ucl.ac.uk/mjh/lionair.png http://nrg.cs.ucl.ac.uk/mjh/lionair.png You can see that both airspeed and altitude misread, in addition to AoA. If I understand correctly, the AoA is used by the ADIRU to correct misreading of the static pressure measured by the pitot-static tubes at high angles of attack. Thus one bad AoA probe can cause lots of symptoms simultaneously.
alkonaut 8y ago
I'm an armchair non-expert at best: but shouldn't planes always be controllable by the column so long as the plane is mechanically OK? I.e. max power + pull stick should always just take the plane up, regardless of any amount of misconfiguration such as being out-of-trim etc? Isn't that a reasonable expectation? That is: a pilot in panic at low altitude should never be required to do anything more than he basically can with hands on throttle and stick, to avoid disaster?
- Shank 8y ago
  > but shouldn't planes always be controllable by the column so long as the plane is mechanically OK? The problem is that you can easily exceed the aircraft flight specifications if you enable unlimited control. If you pull the stick back at max power you can seriously risk the creation of a stall, which is why MCAS exists in the first place. The whole goal Boeing had was to create a safe plane by letting software ensure it was always flying within the safe envelope for mechanical stress. > That is: a pilot in panic at low altitude should never be required to do anything more than he basically can with hands on throttle and stick, to avoid disaster? You would hope this, but what makes the determination that the pilot is at a low altitude? The altimeter tells you where you are in relation to sea level, not the nearest distance to terrain. You could be 10,000 feet above sea level but only 1,000 above a mountain. There's a lot of sensor data you'd have to take into account if you were to try to enable a higher degree of control based on how safe/dangerous it is to give that control.
  - hammock 8y ago
    >what makes the determination that the pilot is at a low altitude? Give the pilot an emergency override button and let him make the judgment call. The whole point of parent comment is that too many sensors and software have removed the pilot's final discretion over the aircraft.
  - drunken-serval 8y ago
    > You would hope this, but what makes the determination that the pilot is at a low altitude Radar altimeter. Any aircraft with autoland capability should have three of them.
phire 8y ago
> Now, from what I understand, appying nose-up electric trim should override MCAS, and so this course of action should be possible. I'm not so sure. Will have to wait for the final report to be sure, but I feel like the Lion Air flight should have survived if the pilot's trim up commands took priority over MCAS's trim down commands. They were fighting it with trim up commands and they lost. I fail to see how they could have lost this fightunless MCAS takes probity. I know MCAS activates in 5 second on, 10 second off cycles and I'm getting the impression that the pilots can only trim up during the 10 second gap.
- treis 8y ago
  You're right, but since 10 > 5 the pilot should always be able to "win". You can see it happening in the Lion Air flight: https://spectrum.ieee.org/image/MzE4Mjg2OQ.jpeg https://spectrum.ieee.org/image/MzE4Mjg2OQ.jpeg I count 20 cycles of MCAS -> Pilot correction. It's not clear why the pilots lost the 21st cycle. It could be that they stopped making corrections or another yet to be identified airplane failure.
  - phire 8y ago
    The MCAS activation just after 23:33:53 pushes the stabiliser down slightly further than it did at any point previously. After this point, the stabiliser looks like it stops responding to trim up commands. The pilots do a few more trim up commands, but the is never a significant upwards response again. Perhaps this is because the pilot's trim up commands appear to be shorter, or perhaps the pilots are pressing the trim up button, hearing a loud girding noise from the electric trim motor as nothing moves, so they stop holding trim up. With all this talk about aerodynamic forces being too strong on the Ethiopian Airlines flight for pilots to manually trim up, I'm wondering if the Lion Air flight experienced aerodynamic forces so strong that even the electric motor was struggling to trim up.
treis 8y ago
>Pilots increase throttle as per non-normal checklist to reduce the risk of stalling due to unreliable airspeed. Pilots disable electric stabilizer trim, as per Boeing's advice, without trimming back to neutral trim. Pilots likely started to trim up with the manual trim wheels, but that's very slow, and gets harder as airspeed increases. I can see that at extreme trim and high speed that it could be difficult to manually trim. What I don't see is how MCAS puts you into that situation. MCAS is supposed to be limited to 2.5 degrees (out of the ~17 degree range) change every 10 seconds. So if you identify a MCAS issue and hit the trim switch, you should still be in a relatively normal flying envelope. I find it hard to believe that manual trim is impossible then. It would have to be a monumental design flaw. In the specific case of the Ethiopian flight, unless I'm mistaken they went through at least a couple cycles of MCAS -> Pilot Correction -> MCAS. Even if they timed their cutoff switch to the end of the MCAS cycle they should only be 2.5 degrees off where they wanted. I would be surprised if that position wouldn't be level flight let alone a situation where they can't manually trim. I wonder if there is a second issue cropping up. The Lion Air crash saw a similar cycle of MCAS -> Pilot Correction -> MCAS that eventually stopped.
- piva00 8y ago
  IIRC the problem with MCAS is that it will "reset" the maximum of 2.5 deg every time it kicks in, so it goes: MCAS kicks in -> apply max 2.5 deg -> pilot correction -> MCAS kick in -> ANOTHER +2.5 deg max, and it goes cycling every 10-20 seconds. At least I recall reading this from some comment here in HN from someone well versed with the 737 MAX.
mhandley 8y ago
Official report is now out: http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+B737-800MAX+%2C%28ET-AVJ%29.pdf http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+... This scenario does indeed appear to be what happened. It just looks like when they re-enabled electric trim, they didn't trim up enough, and then left it turned on. 5 seconds later, MCAS kicked in again, and then it was all over.
- treis 8y ago
  It sounds like they did almost everything right. There are two fateful moments: >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 At this point they were in stable flight and the trim wasn't that extreme. It's not clear whether "manually" here means manual electric trim or trying to physically turn the trim wheel. Up until this point they had correctly diagnosed the issue and taken the proper steps. >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. >At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1.1 and 0.8 units for the remainder of the recording. They re-activated electric trim control but only slightly adjusted it. MCAS kicks in to send them nose down. There's no further pilot correction recorded. Unclear here if there is an airplane issue preventing them from adjusting trim or a pilot error.
  - mhandley 8y ago
    When they did that final electric trim up, the right (more reliable) ASI indicates 365 knots. VMO is 340, so they were already in real trouble. It's not at all clear that even electric trim could overcome the air loads at that point to trim up, though it does look from the graph like it responded slightly.

lysp 8y ago

Does anyone have a mirror of that video?

mhandley 8y ago
This was posted on PPrune: "Originally Posted by infrequentflyer789 Since this video may not be coming back I'll post a sort of transcript from memory since I was lucky enough to get to watch it. I'll try and just describe what I saw and keep my commentary/speculation to a minimum - in <italic>. Bear in mind this is a non-pilot observer's take on it from flaky memory: There is a fair bit of intro talk then the sim. They are in NG sim, not MAX, no surprise there. Mentour in left seat. They start at low altitude, I think it was commented on, not at takeoff, I can't remember if they showed putting flaps up or started with flaps up and said it was just after flaps up. No stick shaker, that I saw. <presume means no elevator feel shift either, and that actual AOA error is not being simulated> IAS disagree then simulated - or they just did the memory items, I didn't notice warning light (not that I would) and he didn't note it, there was an aural alarm but I think that was for AP disconnect <I don't think this is exactly what the accident flights faced, they had shaker and IAS disagree from takeoff> IAS disagree memory items, AP/AT OFF, FDs OFF, 75% N1, 4degrees Throttles are pushed forward to get 75%, he comments that at low alt with denser air this is a lot of thrust and hence speed will increase Trim runs, obviously sim doesn't have MCAS so not sure if they are simulating runaway or if he is doing it with the column switches Comment is made that he was _expecting_ trim to run, because speed is changing, he says it will take a couple of cycles of fighting it with the switches before being definite that it is wrong They discuss (he raises) that he is having flight control issue, they conclude it is trim that is the problem, they now run the stab trim runaway memory items finishing by hitting the switches. At this point he is clearly holding quite a bit of pressure on the column, but not obviously losing control of pitch Now he points out that trim has only got down to (I think) 3 degrees on the indicator (zero being full nose down, I think) and that they are now going to "try something" - video captions say "don't try this at home", like we've all got a FFS in our shed or a 737 on the drive :-) At this point the guy in the right seat uses the handle to wind the trim further _forward_. He stops when he clearly cannot wind it further - but they point out that it's still not at full nose down Mentour is obviously struggling to keep the nose up at this point. I noticed he didn't seem to have the shoulder straps on (right seat did), possibly because he was frequently turning round to talk to the camera. That probably didn't help, but on the other hand he didn't have stick shaker or feel shift to cope with either. Now, with Mentour pulling back, the right seat guy tries to wind the trim back with the handle - and he struggles to move it at all They stop the sim, I think it was after stopping that he noted that at that point they were at 310 (maybe he said 340) knots. I think there was then some further commentary, at one point I think he mentioned the rollercoaster to unload the stab and allow trimming, but commented that close to the ground the instinct is to pull back - I may be imagining that or remembering it from another video though. And that was about it. I can try to answer questions on the video if anyone has any. The eye-opener for me wasn't the force on the control column (which was held anyway), it was that the trim couldn't be moved, in either direction. From somewhere I had got the impression that those wheels had a lot of leverage, due to the gearing, which was why a lot of turns would be required, but it seems that a lot of turns would be required and a gorilla to make them..."
- CamperBob2 8y ago
  Since this video may not be coming back I'll post a sort of transcript from memory since I was lucky enough to get to watch it. I'll try and just describe what I saw and keep my commentary/speculation to a minimum - in <italic>. Bear in mind this is a non-pilot observer's take on it from flaky memory Was the video pulled? Who did that, and why?
  - mhandley 8y ago
    The speculation is that his employer, which flies a lot of 737s, didn't like him using a company simulator to illustrate a safety issue with the 737.
  - colde 8y ago
    He pulled it himself. https://twitter.com/MenTourPilot/status/1113723580284583936 https://twitter.com/MenTourPilot/status/1113723580284583936
    - jillesvangurp 8y ago
      His channel is worth following. He often posts insightful stuff related to incidents with 737s or just general information. He had a nice video about emergency procedures with a total engine failure in (probably) the same simulator just a few weeks ago.
- TheSpiceIsLife 8y ago
  Is anybody here capable of calculating the force required to move the trim tabs on a 737MAX at 310 knots at low altitude? I imagine at that speed there would be quite some force on the elevator and trim tabs.
  - mhandley 8y ago
    There's no trim tab on a 737 - the whole horizontal stabilizer is moved to trim the aircraft in pitch. Normally this is done electrically, but the stabilizer jackscrew can also be moved using manual trimwheels that move the jackscrew using physical cables. Whether this is possible at high airspeed while the stabilizer is trimmed nose down, and the elevator is being pulled up as hard as you can to avoid diving - that's the question that is being raised. Edit: this shows the jackscrew in operation: https://www.youtube.com/watch?v=rxPa9A-k2xY https://www.youtube.com/watch?v=rxPa9A-k2xY
sundvor 8y ago
Not that video, but at least it shows the automatic trim system in action - and is rather educational: https://youtu.be/l62NvkRWa5E https://youtu.be/l62NvkRWa5E . Even better: https://youtu.be/xixM_cwSLcQ https://youtu.be/xixM_cwSLcQ

VBprogrammer 8y ago

The official report will make for interesting reading. The speculation over the last few days is starting to fill in some questions I've had: - Why didn't the pilots identify the issue as MCAS malfunction and follow the guidence? They did and it didn't work for some reason. Possibly because of the air loads on the stabilizer. - Why did the AoA sensor on a new aircraft fail? Suspected bird strike.

woofcat 8y ago
- They did and it didn't work for some reason. Possibly because of the air loads on the stabilizer. Has the CVR transcript been released? I can't find any source on the procedures taken in the cockpit prior to the crash.
- VBprogrammer 8y ago
  I believe the media have been briefed on the the contents of the report but it isn't yet publicly available. It's annoying because I don't trust the media to get the details correct on this type of thing.
peteradio 8y ago
Why is nobody looking at the manufacturer of the sensor?
- VBprogrammer 8y ago
  If someone connected a big industrial stop switch to a solenoid and pointed that solenoid at the trigger of a rifle aimed at the person pressing the button I don't think you would expect anyone to look particularly hard at the person who manufactured the switch. If it was indeed a bird strike which took out the sensor then they seem to be completely beyond all possible blame. Even if it wasn't I'm sure they could point at a host of documentation regarding the usual MTBF of their sensors and why this application was inappropriate.
  - peteradio 8y ago

qaq 8y ago

Why speculate here's memory item (pilot should know without looking at the manual) for all 737s for runaway stabilizer. Do you have any information they followed this. All published information we had was specifically that they did not follow the procedure: CONTROL COLUMN - HOLD FIRMLY AUTOPILOT (if engaged) - DISENGAGE Do not re-engage the autopilot. Control airplane pitch attitude manually with control column and main electric trim as needed If the Runaway Continues STAB TRIM CUTOUT SWITCHES (both) - CUTOUT If the Runaway Continues STABILIZER TRIM WHEEL - GRASP and HOLD

mhandley 8y ago
From today's Ethiopian Airlines press release: "The preliminary report clearly showed that the Ethiopian Airlines Pilots who were commanding FlightET 302/10 March have followed the Boeing recommended and FAA approved emergency procedures to handle the most difficult emergency situation created on the airplane. Despite their hard work and full compliance with the emergency procedures, it was very unfortunate that they could not recover the airplane from the persistence of nose diving. As the investigation continues with more detailed analysis, as usual we will continue with our full cooperation with the investigation team." Edit: perhaps you're refering to the LionAir crash, where they didn't disable stabilzer trim?
- qaq 8y ago
  Thats a press release there is cockpit audio pilots vocalize actions when they take them the cutout switches were never turned off. Would you point to the part of the actual report that says the position of cutout switches was off?
  - mhandley 8y ago
    The preliminary report is not yet public - Ethiopian have seen it, hence their press release, and some of the media have been briefed on its contents, hence the BBC article, but it's not yet public.
    - 8y ago

dingaling 8y ago

A bad AoA probe wouldn't trigger IAS disagreement alert ( that is fed from the separate pitot tubes ) but could activate the corresponding stick-shaker which may make the pilots consider the possibility of IAS uncertainty. Just a minor quibble. Also increasing airspeed isn't a panacea for avoiding a stall, it is entirely possible to enter a high-speed stall if the AoA isn't managed. And in fact as mentioned speed can make recovery more difficult due to airloads on non-FBW aircaft.

VBprogrammer 8y ago
From the AD issued after the Lion Air accident: Additionally, pilots are reminded that an erroneous AoA can cause some or all of the following indications and effects: - Continuous or intermittent stick shaker on the affected side only. - Minimum speed bar (red and black) on the affected side only. - Inability to engage autopilot. - Automatic disengagement of autopilot - IAS DISAGREE alert. - ALT DISAGREE alter. - AOA DISAGREE alert (if the AOA indication option is installed) - FEEL DIFF PRESS light
- dingaling 8y ago
  Thank you for the corrections!
mhandley 8y ago
The bad AoA probe can cause IAS disagree, according to the FAA Emergency Airworthyness Directive: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/83ec7f95f3e5bfbd8625833e0070a070/$FILE/2018-23-51_Emergency.pdf http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/... Take a look at the graphs from the LionAir crash: http://nrg.cs.ucl.ac.uk/mjh/lionair.png http://nrg.cs.ucl.ac.uk/mjh/lionair.png You can see that both airspeed and altitude misread, in addition to AoA. If I understand correctly, the AoA is used by the ADIRU to correct misreading of the static pressure measured by the pitot-static tubes at high angles of attack. Thus one bad AoA probe can cause lots of symptoms simultaneously.

alkonaut 8y ago

I'm an armchair non-expert at best: but shouldn't planes always be controllable by the column so long as the plane is mechanically OK? I.e. max power + pull stick should always just take the plane up, regardless of any amount of misconfiguration such as being out-of-trim etc? Isn't that a reasonable expectation? That is: a pilot in panic at low altitude should never be required to do anything more than he basically can with hands on throttle and stick, to avoid disaster?

Shank 8y ago
> but shouldn't planes always be controllable by the column so long as the plane is mechanically OK? The problem is that you can easily exceed the aircraft flight specifications if you enable unlimited control. If you pull the stick back at max power you can seriously risk the creation of a stall, which is why MCAS exists in the first place. The whole goal Boeing had was to create a safe plane by letting software ensure it was always flying within the safe envelope for mechanical stress. > That is: a pilot in panic at low altitude should never be required to do anything more than he basically can with hands on throttle and stick, to avoid disaster? You would hope this, but what makes the determination that the pilot is at a low altitude? The altimeter tells you where you are in relation to sea level, not the nearest distance to terrain. You could be 10,000 feet above sea level but only 1,000 above a mountain. There's a lot of sensor data you'd have to take into account if you were to try to enable a higher degree of control based on how safe/dangerous it is to give that control.
- hammock 8y ago
  >what makes the determination that the pilot is at a low altitude? Give the pilot an emergency override button and let him make the judgment call. The whole point of parent comment is that too many sensors and software have removed the pilot's final discretion over the aircraft.
- drunken-serval 8y ago
  > You would hope this, but what makes the determination that the pilot is at a low altitude Radar altimeter. Any aircraft with autoland capability should have three of them.

phire 8y ago

> Now, from what I understand, appying nose-up electric trim should override MCAS, and so this course of action should be possible. I'm not so sure. Will have to wait for the final report to be sure, but I feel like the Lion Air flight should have survived if the pilot's trim up commands took priority over MCAS's trim down commands. They were fighting it with trim up commands and they lost. I fail to see how they could have lost this fightunless MCAS takes probity. I know MCAS activates in 5 second on, 10 second off cycles and I'm getting the impression that the pilots can only trim up during the 10 second gap.

treis 8y ago
You're right, but since 10 > 5 the pilot should always be able to "win". You can see it happening in the Lion Air flight: https://spectrum.ieee.org/image/MzE4Mjg2OQ.jpeg https://spectrum.ieee.org/image/MzE4Mjg2OQ.jpeg I count 20 cycles of MCAS -> Pilot correction. It's not clear why the pilots lost the 21st cycle. It could be that they stopped making corrections or another yet to be identified airplane failure.
- phire 8y ago
  The MCAS activation just after 23:33:53 pushes the stabiliser down slightly further than it did at any point previously. After this point, the stabiliser looks like it stops responding to trim up commands. The pilots do a few more trim up commands, but the is never a significant upwards response again. Perhaps this is because the pilot's trim up commands appear to be shorter, or perhaps the pilots are pressing the trim up button, hearing a loud girding noise from the electric trim motor as nothing moves, so they stop holding trim up. With all this talk about aerodynamic forces being too strong on the Ethiopian Airlines flight for pilots to manually trim up, I'm wondering if the Lion Air flight experienced aerodynamic forces so strong that even the electric motor was struggling to trim up.

treis 8y ago

>Pilots increase throttle as per non-normal checklist to reduce the risk of stalling due to unreliable airspeed. Pilots disable electric stabilizer trim, as per Boeing's advice, without trimming back to neutral trim. Pilots likely started to trim up with the manual trim wheels, but that's very slow, and gets harder as airspeed increases. I can see that at extreme trim and high speed that it could be difficult to manually trim. What I don't see is how MCAS puts you into that situation. MCAS is supposed to be limited to 2.5 degrees (out of the ~17 degree range) change every 10 seconds. So if you identify a MCAS issue and hit the trim switch, you should still be in a relatively normal flying envelope. I find it hard to believe that manual trim is impossible then. It would have to be a monumental design flaw. In the specific case of the Ethiopian flight, unless I'm mistaken they went through at least a couple cycles of MCAS -> Pilot Correction -> MCAS. Even if they timed their cutoff switch to the end of the MCAS cycle they should only be 2.5 degrees off where they wanted. I would be surprised if that position wouldn't be level flight let alone a situation where they can't manually trim. I wonder if there is a second issue cropping up. The Lion Air crash saw a similar cycle of MCAS -> Pilot Correction -> MCAS that eventually stopped.

piva00 8y ago
IIRC the problem with MCAS is that it will "reset" the maximum of 2.5 deg every time it kicks in, so it goes: MCAS kicks in -> apply max 2.5 deg -> pilot correction -> MCAS kick in -> ANOTHER +2.5 deg max, and it goes cycling every 10-20 seconds. At least I recall reading this from some comment here in HN from someone well versed with the 737 MAX.

mhandley 8y ago

Official report is now out: http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+B737-800MAX+%2C%28ET-AVJ%29.pdf http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+... This scenario does indeed appear to be what happened. It just looks like when they re-enabled electric trim, they didn't trim up enough, and then left it turned on. 5 seconds later, MCAS kicked in again, and then it was all over.

treis 8y ago
It sounds like they did almost everything right. There are two fateful moments: >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 At this point they were in stable flight and the trim wasn't that extreme. It's not clear whether "manually" here means manual electric trim or trying to physically turn the trim wheel. Up until this point they had correctly diagnosed the issue and taken the proper steps. >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. >At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1.1 and 0.8 units for the remainder of the recording. They re-activated electric trim control but only slightly adjusted it. MCAS kicks in to send them nose down. There's no further pilot correction recorded. Unclear here if there is an airplane issue preventing them from adjusting trim or a pilot error.
- mhandley 8y ago
  When they did that final electric trim up, the right (more reliable) ASI indicates 365 knots. VMO is 340, so they were already in real trouble. It's not at all clear that even electric trim could overcome the air loads at that point to trim up, though it does look from the graph like it responded slightly.