Re:Boeing's Managerial Revolution Created the 737 Max Disaster
by mannykannot on Saturday September 21, 2019 @10:57PM
(#21039353)
Firstly, on previous variants, opposing the trim runaway with the yoke was sufficient to cut out the electric trim, but this was necessarily changed for MCAS-commanded trim changes. It is conceivable that a trim runaway might not be stopped by that action, but it is apparently highly unlikely -- such situations are apparently not part of current 737 simulator training [1].
This is significant, because stopping a runaway by opposing it with the yoke leaves the airplane close to being in trim, and toggling the cutout switches becomes a clean-up operation to prevent a recurrence. This, apparently, is as far as pilot simulator training for trim runaway goes. In the case of MCAS, however, toggling the swiches is the only way to stop it, and it leaves the airplane significantly out of trim.
This is what the Ethiopian Airlines flight crew did, but then they found it impossible to put the airplane back in trim because the load on the stabilizer jackscrew was resisting their attempts at manual trimming. This problem is mentioned in the documentation (though not, significantly, in the checkist that the FAA's response to the Lion Air crash directed pilots' attention to), but in that documentation, it rather vaguely says this might be a problem, and if so, it might be necessary to pitch the airplane further in the direction of the mis-trim to reduce the load on the jackscrew so that it can be cranked in manually. It suggests that several cycles may be necessary to complete the action.
If you are, as the Ethiopian Airlines crew were, at low alttude in an airplane mis-trimmed to dive, this is not a viable option, which is why they re-engaged the electric trim in the hope of correcting the problem. The article mentions a video, that was briefly available, of an exercise to test this scenario, in which the professional pilots struggled to maintain control.
It is clear from this that MCAS runaway is sufficiently different from the sort of trim runaways that pilots have previously experienced, either for real or in their simulator training, and this alone should arguably have been sufficient reason for additional training to prepare for MCAS failure. Even after the Lion Air crash, the response of Boeing and the FAA failed to make this distinction clear -- the message was 'this is merely a form of trim runaway, just like what you have trained for', which it is not.
And then there is the separate issue of not using both AofA inputs, apparently just to keep the lie that there was nothing about MCAS that pilots needed to know about.
None of the above is my own opinion - they are issues that professional pilots, engineers and safety experts have forcefully raised. Captain Dan Carey himself initially went along with Boeing's take on the issue, until more information about the issue came out. If you have contrary experience of 737 training and operation, your point of view would be most welcome.
This is significant, because stopping a runaway by opposing it with the yoke leaves the airplane close to being in trim, and toggling the cutout switches becomes a clean-up operation to prevent a recurrence. This, apparently, is as far as pilot simulator training for trim runaway goes. In the case of MCAS, however, toggling the swiches is the only way to stop it, and it leaves the airplane significantly out of trim.
This is what the Ethiopian Airlines flight crew did, but then they found it impossible to put the airplane back in trim because the load on the stabilizer jackscrew was resisting their attempts at manual trimming. This problem is mentioned in the documentation (though not, significantly, in the checkist that the FAA's response to the Lion Air crash directed pilots' attention to), but in that documentation, it rather vaguely says this might be a problem, and if so, it might be necessary to pitch the airplane further in the direction of the mis-trim to reduce the load on the jackscrew so that it can be cranked in manually. It suggests that several cycles may be necessary to complete the action.
If you are, as the Ethiopian Airlines crew were, at low alttude in an airplane mis-trimmed to dive, this is not a viable option, which is why they re-engaged the electric trim in the hope of correcting the problem. The article mentions a video, that was briefly available, of an exercise to test this scenario, in which the professional pilots struggled to maintain control.
It is clear from this that MCAS runaway is sufficiently different from the sort of trim runaways that pilots have previously experienced, either for real or in their simulator training, and this alone should arguably have been sufficient reason for additional training to prepare for MCAS failure. Even after the Lion Air crash, the response of Boeing and the FAA failed to make this distinction clear -- the message was 'this is merely a form of trim runaway, just like what you have trained for', which it is not.
And then there is the separate issue of not using both AofA inputs, apparently just to keep the lie that there was nothing about MCAS that pilots needed to know about.
None of the above is my own opinion - they are issues that professional pilots, engineers and safety experts have forcefully raised. Captain Dan Carey himself initially went along with Boeing's take on the issue, until more information about the issue came out. If you have contrary experience of 737 training and operation, your point of view would be most welcome.
[1] https://www.youtube.com/watch?v=SvpAsiwdM_E