FAA to meet with U.S. airlines, pilot unions on Boeing 737 MAX
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This is the first in an excellent, IMO, series of videos on this topic.
https://youtu.be/AgkmJ1U2M_Q
Thanks for that, very interesting even for a layman like me.
Bob, I have about 30 hours in a PA28 about 33 years ago. So, I'm possibly more of a layman than most here, but aviation is fascinating. I just wish it didn't need mistakes like this to attract interest from the masses.Quote:
Originally Posted by bob10
Also, I hope that Boeing, who deserve the reputation they have built over more than 100 years, don't fall due to this.
The opening minute or so of the above video seems to imply that the stabiliser screwjack is to blame, whereas it definitely is NOT.
The screwjack at full nose-down position is not because of a fault or mechanical failure, but is most likely a result of the MCAS driving it there (basically what I have written in previous posts).
If the Stab Trim Cutout switches had been left in the cutout position (as per the checklist), we wouldn't be having this discussion [smilebigeye] However, it appears the crew decided to become test pilots and switch it back on. Yes, the FO said the manual trim could not be moved. Did he extend the handle and try, or did he only try to rotate the wheel on its own? (all but impossible). The manual trim requires a LOT of effort to move. In such a situation, both pilots could have extended their handles and should have been able to move it manually together. It does not appear they tried that, but instead just switched the cutoff switches back on.
The aircraft by that time was well above Vmo - is it still possible to manually trim at that speed, and even if it is, is it possible to do so fast enough when that close to the ground?
An old (not bold!) pilot told me that the most important mathematical equation in flying is the relationship between a) time to identify and fix the problem, and b) time to impact. Seems to me, that in both cases, the lack of pilot training in the MCAS failure, meant that that equation was weighted too far to one side. Very very sad
I’m not sure, but I imagine ‘yes’. The fastest I’ve been when dealing with a runaway stabiliser (in the simulator) is about 330kt. That’s just below Vmo in the -800NG.Quote:
Originally Posted by JDNSW
We had to do it with one pilot flying and one trimming. The resistance is not that bad, but it’s very tiring because there are a LOT of turns to to get a trim change. I coordinate it in lots of 10 rotations “ten forward.... ten back...” or similar.
The need to trim is greatest as you configure for landing. You need lots of forward trim as you run the flaps out. So typically you would set up on a longer than usual final and start to configure/trim early. We have to be stable by 1000’ AGL. In a situation with manual trimming, I’d want to be stable by 3000-2000’.
From what I understand, they were in the vicinity of 390kt. Another factor which may have exacerbated the problem is mach tuck. That’s when the centre of pressure moves aft with increasing mach number (creating a pitch-down tendency).
That’s only a theory of mine. The 737 has speed trim and mach trim - both of which act through the stab trim, and therefore are inoperative if you switch the stab trim cutout switches to cutout. So it’s possible that if the aircraft had been slowed (within reason, say 250kt) that some of the pitch-down tendency may have been reduced, and given back some pitch control. The last 2 paragraphs are all theorising on my part...
According to what has been published, the speed at the time was 360 ->380kts. The trim from full nose down to neutral is 125 turns. I think slowing down was not possible in the circumstances - at that speed even if the elevators were sufficiently powerful, which I gather they are not, the control load would have been impossible for one pilot (the other on the trim).
It seems to me that they were in a virtually unrecoverable situation before they realised it was a serious problem.