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All the pilots needed to do was identify the problem as MCAS, use manual electric trim buttons to neutral and then turn electric trim off. But Boeing never tra
by phire 7y ago
All the pilots needed to do was identify the problem as MCAS, use manual electric trim buttons to neutral and then turn electric trim off.
But Boeing never trained pilots how to identify the problem, and told them the old procedure was the correct way of dealing with it.
The old procedure told pilots to turn electric trim off, never turn it back on and return stabilizes to neutral with manual control, which turns out to be impossible.
That's not one, but two pilot training issues with Boeing's official training materials.
A related problem is that because of the no extra training requirements, Boeing explicitly designed MCAS to be near impossible to disable, because if it was disabled then the plane now had different flight characteristics, which the pilots weren't trained to handle.
And this is also the reason why MCAS only used data from one sensor. If the sensors disagreed and MCAS disabled itself, then that would require pilot training.
The whole system would have been designed differently, and more safely if it wasn't for the "no extra training" requirement.
- idoubtit 7y agoIt was much worse than a lack of training. Prior to the first crash in Indonesia, MCAS was not mentioned in the formation to the pilots. Boeing has asked the FAA to remove it from the documentation. The FAA did not know that the MCAS was totally different from what Boeing had initially planed, so they agreed. After the crash, Boeing published new instructions that mentioned MCAS. But they were of no use for the Ethiopian crash. As you wrote, turning off MCAS also turned off stabilisation, and manual control was not possible because of the excessive speed. The pilots did understand that, so they enabled the electric trim again. Unfortunately, this activated the MCAS which send the plane downside 10 seconds later. They had no way out.
- phire 7y agoI have a personal theory (based on the graphs from the reports from both crashes) that once the stabilisers go far enough out of trim at high enough speeds, that the even electric trim motor isn't powerful enough to move the stabiliser. In both crashes, after repeated activations of MCAS has pushed the stabiliser almost fully down, we see the pilots do two quick presses of the trim up button. The graph shows the stabiliser barely moving (much less than a press of the same length earlier in the flight). I suspect the pilots pressed the trim up button, heard a loud noise from the electric motor straining, or a fuse popping, or something? So they stopped pressing trim up. Even worse, only trim up was failing, MCAS was still able to command more trim down.
- Bendingo 7y agoBest summary I've read so far, of the whole fiasco.