Quote:
Originally Posted by Skybird
Latest theory is about blowback, meaning that the plane gained so much speed that the airstream hitting the ailerons defeated the hydraulic pressure of the system trying to move them - the plane than practically is uncontrollable and cannot be saved by pilot input if it does not by lucky events loose speed again before the hydraulic system suffered unrepairable damage already.
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What caused the pilot not to be able to be recovered was the trim system being too powerful, exerting forces too great for pilots to overcome, even at normal flying speeds. This has been a possibility during the entire 737 series manufacture, over 30 years.
In the event of a trim overrun, the stabilizer trim cutout switch is and has been in the same exact location all that time. Throwing that switch results in immediate recovery of the pilot's ability to fly the plane, as shown in the flight previous to the fatal crash, where a third pilot in the jump seat evaluated the problem and knew what to do. As blancolirio said in the video I posted, it was the addition of the pilot in the jump seat that made the difference.
The plane can be flown safely. Now it's up to Boeing to ensure that it always is. Pilot error can crash any plane. This was clear pilot error. The question is "was the pilot error a predictable consequence of Boeing's or the airline's procedures, and what must be changed to keep this from happening again?"
From Boeing's standpoint, the trim system is too powerful. The trim system is more powerful than any possible pilot input. A pilot should be able to overcome the trim by using stick position only, thereby buying the time to analyze the problem in a stress-free mindset.
Secondly, with two angle of attack sensors outside the fuselage, hooking only one of them to the MCAS system just makes no sense. Error handling is absolutely essential to the functioning of any system and unquestioningly accepting the word of a malfunctioning sensor with no backup is an obvious failing.
Then the decision to have two systems, the light indicating autopilot/angle of attack sensor disagreement and the cockpit angle of attack display as optional equipment is also obviously faulty.
The kicker is that Boeing already advised pilots that MCAS malfunctions should be treated as a trim overrun situation and the stabilizer trim cutout switch should be switched off. Simple simulator runs should have revealed the fact that in an MCAS malfunction, the pilot is simply too busy trying to save his and his passengers' lives to think clearly.
The information you need to know to understand this situation is in the video I provided. It is self-validating, from a professional pilot who knows his business.