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Thechnically they could have used the thumb switch and regained level flight to override the mcas system temporarily and then shut off the electrical system to
by weaksauce 8y ago
Thechnically they could have used the thumb switch and regained level flight to override the mcas system temporarily and then shut off the electrical system to the stab and trim manually thereafter. However, they didn’t know about the mcas system and the troubleshooting steps that Boeing has for that mode of failure were insufficient for this precise scenario.
- fgonzag 8y agoAt 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. It seems they tried it but MCAS kicked 5 seconds after they turned on the electrical trim. They didn't have enough time to correct the stabilizer. I don't know how fast returning a stabilizer to neutral position can be done, but they probably thought they had more than 5 seconds. They were probably going to turn off electronic trim control afterwards.
- cjbprime 8y agoI've read that it takes the trim motor 30 seconds to move the jackscrew completely along its path. It was found all the way at one end in the wreck. So naively, it takes up to 15 seconds of continuous motor operation to recover level flight.
- JRKrause 8y agoThe manual electric trim inputs override the MCAS inputs[0], so they could have kept applying the appropriate trim regardless of the MCAS malfunction. [0] Appendix 1, 05:40:30 (You can see the AND command being canceled by the pilots manual electric ANU command)
- makomk 8y agoIt only overrides the MCAS inputs when they're actively adjusting the trim. So, they did try and correct the trim with the manual inputs, and five seconds after the last push of a trim adjust button the malfunctioning MCAS activated and adjusted the trim to something far worse than when they'd started. If I'm reading this right, the plane hit the ground killing everyone on board less than 30 seconds later.
- JRKrause 8y agoRefer to the graph on Appendix 1, the automatic AND commands begin about 5 minutes before the crash. They counter them partially with the manual ANU electric trim for the first 1.5 minutes before issuing STAB CUTOUT.
- holler 8y agothis may be a naive question but with all of the advanced technology on these planes, why isn't there a check for altitude before any automated command runs which says "hey we just took off, are 400ft above ground, MCAS is saying nose down, we will crash if that command runs, CANCEL"
- cjbprime 8y agoYou'll 100% for sure crash if you stall at 400ft above ground. MCAS is designed to prevent stalls.
- deleted 8y ago[deleted]
- Rooster61 8y agoNot at take-off. See above comment about flaps.
- javagram 8y agoMCAS system is supposed to stop the plane from stalling. The faulty AoA sensor is causing the plane to think it’s about to stall and therefore MCAS works as designed to prevent the pilot from putting the plane into a stall. Of course the design is wrong because the plane is actually pointing toward the ground and MCAS thinks it’s pointing to the sky...
- robryan 8y agoWhat about a single button to turn MCAS off and return to trim to a neutral position? Or a setting where the pilot is telling the system to ignore the sensor input. Maybe a bit like a self driving car planes will eventually have a system where they can use visual markers as a check on what sensors are reporting.
- weaksauce 8y agoThat may be where they will go with this but it may require a new certification and training.