4 ms·

Runaway trim is supposed to be part of the "memory checklist" for pilots. The symptoms of MCAS are the same as runaway trim and the fix is the same (which is wh

by jquery 8y ago

Runaway trim is supposed to be part of the "memory checklist" for pilots. The symptoms of MCAS are the same as runaway trim and the fix is the same (which is why Boeing didn't feel like extra pilot training was needed), so I'm curious to see the most recent investigation and hear the black box voice recorder. Did they not know they were dealing with runaway trim? Did they think it was something else? Did they forget the memory checklist? Was there not enough height to deal with runaway trim regardless? Were the symptoms different than runaway trim, confusing the pilots? The black boxes will be very illuminating on this respect, especially since we never recovered the Lion Air black box voice recorder.

qyv 8y ago
You are correct. And if two crews in 5 months had the same issue either identifying or dealing with the same problem, then perhaps there is an design or training problem error here.
- ineedasername 8y ago
  No need to choose, it seems like design and training can share the spot light, with their third friend sensor failure.
cybrjoe 8y ago
A quick search indicates the CVR for Lion Air 610 was recovered. Did I miss something?
- jquery 8y ago
  You're right, looks like it was recovered earlier this year, and they haven't released the transcript yet. https://www.reuters.com/article/us-indonesia-crash/no-public-details-on-crashed-lion-air-voice-recorder-until-final-report-indonesian-official-idUSKCN1PG08R https://www.reuters.com/article/us-indonesia-crash/no-public...
ricardobeat 8y ago
> [MCAS] it’s not stopped by the pilot pulling the yoke, which for normal trim from the autopilot or runaway manual trim triggers trim hold sensors This implies that 'normal' runaway trim can be stopped by pulling the control yoke. Maybe pilots simply have no idea what is going on once they realise that action has no effect with the MCAS?
- argd678 8y ago
  > “After this horrific Lion Air accident, you’d think that everyone flying this airplane would know that’s how you turn this off,” said Steve Wallace, the former director of the U.S. Federal Aviation Administration’s accident investigation branch. I suspect the other factors will answered when this question is answered too.
- inferiorhuman 8y ago
  This implies that 'normal' runaway trim can be stopped by pulling the control yoke. Pulling on the yoke will only stop the 737's computers from moving the stabilizer IF it's the speed trim system (STS) that's moving the stabilizer. Otherwise the yoke is intended to adjust the elevator not the stabilizer
salex89 8y ago
True... Now I'm wondering has the third pilot been able to help because he was trained better, didn't forget the memory items, or was just in that position. He was likely sitting far back, he wasn't wrestling the plane (I'm not sure how composed is the cabin during those maneuvers). He might been in a better position to see whatever was happening.
nas 8y ago
This Seattle Times article is quite informative: https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/ https://www.seattletimes.com/business/boeing-aerospace/faile... It seems the MCAS had a flawed design where it would move the trim further than expected and would also trigger multiple times. Based on my understanding, the MCAS would have been quite safe if it didn't have these flaws (pilots deal with a failed AoA sensor as another case of "runaway trim").
inferiorhuman 8y ago
The symptoms of MCAS are the same as runaway trim No, they're not.
- kayfox 8y ago
  So, how are they not?
  - inferiorhuman 8y ago
    So, how are they not? When you hit the trim buttons on the yoke MCAS stops for five seconds. What Boeing considers runaway trim would not stop when you counter with the trim buttons.
    - blackflame7000 8y ago
      Yea the interval is actually 20 seconds which is a really long time to a pilot thinking he is in an emergency. If you look at the period of the ups and downs of the Ethiopian flight they roughly correspond to that 20-second interval. Just when he thinks he's fixed it, it strikes again and again, taking a more aggressive nose down attitude each time.
    - kayfox 8y ago
      So, if the trim were running away based on an intermittent fault, the same situation could be encountered because the pilots don't need to execute the runaway trim checklist?
  - Someone1234 8y ago
    It feels different from their runaway stabilizer training. MCAS has a delay between each motion, whereas a runaway stabilizer is much more aggressive.

by jquery 8y ago

qyv 8y ago

You are correct. And if two crews in 5 months had the same issue either identifying or dealing with the same problem, then perhaps there is an design or training problem error here.

ineedasername 8y ago
No need to choose, it seems like design and training can share the spot light, with their third friend sensor failure.

cybrjoe 8y ago

A quick search indicates the CVR for Lion Air 610 was recovered. Did I miss something?

jquery 8y ago
You're right, looks like it was recovered earlier this year, and they haven't released the transcript yet. https://www.reuters.com/article/us-indonesia-crash/no-public-details-on-crashed-lion-air-voice-recorder-until-final-report-indonesian-official-idUSKCN1PG08R https://www.reuters.com/article/us-indonesia-crash/no-public...

ricardobeat 8y ago

> [MCAS] it’s not stopped by the pilot pulling the yoke, which for normal trim from the autopilot or runaway manual trim triggers trim hold sensors This implies that 'normal' runaway trim can be stopped by pulling the control yoke. Maybe pilots simply have no idea what is going on once they realise that action has no effect with the MCAS?

argd678 8y ago
> “After this horrific Lion Air accident, you’d think that everyone flying this airplane would know that’s how you turn this off,” said Steve Wallace, the former director of the U.S. Federal Aviation Administration’s accident investigation branch. I suspect the other factors will answered when this question is answered too.
inferiorhuman 8y ago
This implies that 'normal' runaway trim can be stopped by pulling the control yoke. Pulling on the yoke will only stop the 737's computers from moving the stabilizer IF it's the speed trim system (STS) that's moving the stabilizer. Otherwise the yoke is intended to adjust the elevator not the stabilizer

salex89 8y ago

True... Now I'm wondering has the third pilot been able to help because he was trained better, didn't forget the memory items, or was just in that position. He was likely sitting far back, he wasn't wrestling the plane (I'm not sure how composed is the cabin during those maneuvers). He might been in a better position to see whatever was happening.

nas 8y ago

This Seattle Times article is quite informative: https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/ https://www.seattletimes.com/business/boeing-aerospace/faile... It seems the MCAS had a flawed design where it would move the trim further than expected and would also trigger multiple times. Based on my understanding, the MCAS would have been quite safe if it didn't have these flaws (pilots deal with a failed AoA sensor as another case of "runaway trim").

inferiorhuman 8y ago

The symptoms of MCAS are the same as runaway trim No, they're not.

kayfox 8y ago
So, how are they not?
- inferiorhuman 8y ago
  So, how are they not? When you hit the trim buttons on the yoke MCAS stops for five seconds. What Boeing considers runaway trim would not stop when you counter with the trim buttons.
  - blackflame7000 8y ago
    Yea the interval is actually 20 seconds which is a really long time to a pilot thinking he is in an emergency. If you look at the period of the ups and downs of the Ethiopian flight they roughly correspond to that 20-second interval. Just when he thinks he's fixed it, it strikes again and again, taking a more aggressive nose down attitude each time.
  - kayfox 8y ago
    So, if the trim were running away based on an intermittent fault, the same situation could be encountered because the pilots don't need to execute the runaway trim checklist?
- Someone1234 8y ago
  It feels different from their runaway stabilizer training. MCAS has a delay between each motion, whereas a runaway stabilizer is much more aggressive.