IIRC, the pilot increased thrust to increase airspeed which made it harder to pull back on the yoke to fight against MCAS. I will need to check references again but I just got into bed.

Edit: here we go: Pilots have demonstrated in simulator that the trim wheels cannot be moved in severe mis-trim conditions combined with a high airspeed.[92][93] As the pilots on Flight 302 pulled on the yoke to raise the nose, the aerodynamic forces on the tail’s elevator would create an opposing force on the stabilizer trim jackscrew that would prevent the pilots from moving the trim wheel by hand.[86][91][94]

The resolution for this jammed trim issue is not part of Boeing's current 737 manual according to The Air Current.[90] The Seattle Times reports pilots on the 737-200 were trained for this failure, but latter models got so reliable, this procedure was no longer necessary.[91][90]

Just stolen from Wikipedia before I sleep: https://en.m.wikipedia.org/wiki/Ethiopian_Airlines_Flight_30...

"Unable to trim": https://youtube.com/watch?v=aoNOVlxJmow

The drop in altitude occurred because of MCAS activations retrimming the plane into a dive. MCAS is only active during flaps retracted flight regimes.

They couldn't redeploy the flaps to shutdown MCAS because

A) they didn't know it would work, and it was not documented in any standard procedure

B) the plane was travelling too fast for safe flap deployment

C)Flap deployment decreases the critical AoA of the wing, meaning that pilots would have to be extremely careful during the recovery, and may in fact not have been able to pull out fast enough even if they fixed the mistrim.

Also, remember that a plane flying straight at the ground is still making lift as it barrels toward the earth. Lift isn't something magic that guarantees the plane stays away from the ground. The force vector will happily accelerate you 90° relative to your lifting surface's velocity vector through the fluid.

If for whatever reason you decide that that vector should no longer be parallel to the surface... Well... That's on you.

Or in this case, a computer programmed with an insufficiently robust algorithm for safely doing what it was actually meant to do. As the flight computer had no way of understanding that what its AoA sensor was telling it could possibly be wrong, and therefore alerting the pilots that they were flying on their own now.

So while the pilots knew what they wanted, the computer, not being programmed with the possibility of being wrong in mind, did exactly as it was designed to do.

And this, ladies and gentlemen, is how you kill 300 people without realizing that you're doing it.

> the altitude seems to stabilize. So why the sudden drop before the crash?

> There must be a sudden behavioural change of the plane or the pilots right before it went down

The altitude was stable because the pilot valiantly countered the AND (aircraft nose down) trim input from MCAS with ANU trim (using the electric trim switch) again and again and again. And again.

From what I gather, he then handed the plane off to the copilot to look things up in the QRH (Quick reference handbook, checklists basically), and unfortunately the copilot did not trim up quite as stubbornly, allowing MCAS to trim down so much as to be unrecoverable with elevator control forces alone. Truly terrible.

> Second question: why did they retract the flaps? Wouldn't the wings generate more lift with flaps extended?

Standard operating procedure after the initial climb, you retract flaps. Yes, wing would generate more lift with flaps, but that’s not the problem if you’re pointing downward.

Having said that, deploying flaps would have inhibited MCAS and allowed them to control the plane, maybe, but they didn’t know that.

EDIT to add: I’m talking about the doomed Lion Air flight here (which the FDR data plot linked above pertains to, if I’m not mistaken).

> Wouldn't the wings generate more lift with flaps extended?

Sure, until they get ripped off at speed. Flaps aren't a magic "more lift plz" button.