Originally Posted by
symbian simian
If the FO had not touched the switches, the crash might not have happened. He touched the switches (AFAIR) 3 times, for about half a second each, and MCAS replied 3 times with about 4.5 degrees AND, had he not trimmed, MCAS would not have acted up again. Obviously the crew did not handle this anywhere near competently, but I do think some people at B willfully tried to hide the extent of what MCAS was capable of from the FAA, and didn't realize themselves how bad of a design it was. The reason they made it dependant on 1 AOA as opposed to comparing both was to prevent having a miscompare annunciator, and another checklist, and that would have added training (on the KC-46 MCAS uses both AOAs, but for the 737 they took that out). Just one questionable practice to save money.
You’re understanding of MCAS as it functioned at the time is incorrect. MCAS would activate at a high AoA an run until AoA was decreased below a preset value (low Alt roughly 5.0). Use of the Main Elec trim stops MCAS then once Main Elec Trim is no longer commanded 5 sec later MCAS is allowed to run again. If he had not engaged the MAIN Elect trim the Stabilizer would have run the the nose down limit for that phase of flight uninterrupted.
Contrary to you assertion if either crew member had held down the trim switch continually until they were able to get the Stab Trim Cutout selected that would have stopped the movement of the stab. (Unless the were against the column cutout then they would have gotten stab movement in the direction commanded by the Main Elect trim until column force was reduce and they came off the column cutout)
I believe the KC-46 has synthetic airdata used as a tie breaker. Engineers at Boeing are on the record asking for that to have been added to the 737 Max after the MCAS activation window was changed to include low altitude / low airspeed. (I believe at least one engineer quit after a safety meeting over this and another fire warning issue on a different aircraft). Either way including a comparator between the 2 AoA might have required time and money but an updated Safety Risk Assessment should have mandated it. Boeing intentionally did not provide the change in the safety assessment to the FAA. They did explain MCAS to the AEG (aircraft evaluation group) but did not update them with a new Assesment as required or inform them that the MCAS activation parameters had been changed to include low speed stalls. The fix that took them 2 years could have been incorporated in the original plane with minor delays. BOEING chose to cut corners and risk lives. Then they doubled down on it after Lion Aio when they looked at the new data that showed 15 more crashes would be likely in the life of the aircraft. Boeing figured that with a crash every 2 years they could get a fix out before the next one…. They were wrong and it was other peoples lives they were staking their bet on.