[EdiX]

> The planes are already unmanageable, even if MCAS is fixed: human pilots aren't strong enough to turn the trim wheels manually in an emergency.

Operation of the trim wheel and the forces acting on it are the same as the 737 NG. If this worries you, you shouldn't take any 737.

The wheel in that video can not be turned manually because of the aerodynamic forces acting on it. Pilots are trained extensively to recognize a runaway trim condition and stop it before it gets to that point. At lower angles a roller coaster maneuver can be used to turn the trim manually.

The MCAS was definitely poorly designed but everyone is downplaying the poor pilot response and maintenance issues involved with the crash. Lion Air pilots flew a plane with a stall warning going on for a full hour instead of landing ASAP. Then when the plane got to the ground, the company saw it fit to fill it up with people again and fly it with a critical system malfunctioning due to unknown causes.

They dodged responsibility because boeing had a serious design issue but their behavior was criminal, even more so than boeing. I wouldn't fly any lion air plane.

[phs318u]

Boeing’s own testing assumed pilots respond to runaway trim situation within 4 seconds [0]. Beyond that, the MCAS will have put the plane in an aerodynamic position where the pilot forces required to manually stabilise are too great. 4 seconds is not a lot of time. The Ethiopian pilots were aware of the need to disengage the powered trim and use manual control. They just couldn’t force the controls enough given the position the plane was in. The 737MAX is a death trap. It won’t fly again without significant redesign.

[0]. http://www.b737.org.uk/mcas.htm

[HarryHirsch]

On the other hand, the AOA sensor on the Ethiopian Airlines plane failed at takeoff, likely due to birdstrike. Birdstrike isn't supposed to crash an aircraft.

The speaker talks about trimwheel behaviour. Pilots train for runaway stabilizer trim, but that's continuous movement of the trimwheel, faulty MCAS looks much like regular speedtrim. Also, activating electric trim activates another round of MCAS. Obviously you shouldn't take Lion Air, but after this talk Boeing doesn't look safe now either.

[EdiX]

Broadly speaking, I agree with you. I was responding to the hysteria about the trim wheel in this thread. I'm getting the impression that some users think the trim wheel, or its behavior under extreme aerodynamic conditions, is a "new" design flaw unique to the 737 MAX when in fact almost every airliner in existence has a trim wheel behaves like that.

The exception being modern fly-by-wire planes that simply don't have an option of manual override.

    The speaker talks about trimwheel behaviour. Pilots train for runaway stabilizer trim, but that's continuous movement of the trimwheel, faulty MCAS looks much like regular speedtrim

Empirically, the Lion Air plane exhibited the same MCAS behavior on its last (successful) flight. So it's at least possible for pilots to recognize it as a runaway trim and act accordingly.

    Obviously you shouldn't take Lion Air, but after this talk Boeing doesn't look safe now either. 

After reading the Lion Air report my conclusion is that the MCAS was poorly designed but it's also an easily fixed problem on an otherwise safe design and there's so much focus on boeing that they will take action and fix it. Meanwhile nobody cares about Lion Air and if they keep flying broken airplanes eventually they're going to kill more people, with or without MCAS.

[salawat]

Note the penultimate Lion Air flight had a third-pilot dead-heading in the cockpit. Not a regular luxury.

Also, the AoA-vane was replaced with a faulty part, and never retested after install if I recall correctly. A procedure complicated by the fact the plane would have had to have been started, shutdown, then restarted since the Flight Computer switches from side-to-side each flight.

So a maintenance tech may have accidentally tested the wrong computer assuming the documentation wasn't up to snuff. Can't say as I've seen that part of the documentation myself; but considering they left MCAS out of the pilot docs, I somehow doubt that it was greatly elaborated on in the maintenance docs as well.

[magduf]

I think that 3rd pilot was key not just because of an extra person; IIRC, he had a vantage point the pilots didn't have, and saw what was going on with the trim wheels.

[magduf]

The 737 should have been retired decades ago. It's an utterly primitive aircraft, and its cockpit hasn't changed significantly since the 1960s. Newer Boeing aircraft don't have those trim wheels at all. Even the old DC-9 didn't have them.