[msbarnett]

> And, the crew left the power setting at climb throughout almost the entire sequence, so they oversped the airframe.

I believe that's correct given that they had an Unreliable Airspeed Indicator warning (due to the malfunctioning AoA sensor), per the memory items on the UAI checklist.

It makes the forces on the trim wheel much worse, which explains why they couldn't turn it, but it's the correct checklist response to the conditions observed, and the Boeing/FAA directive completely failed to take the impact of this response into account.

[VBprogrammer]

> I believe that's correct given that they had an Unreliable Airspeed Indicator warning (due to the malfunctioning AoA sensor), per the memory items on the UAI checklist.

The idea that a pilot would knowingly leave thrust at climb power while in modestly level flight at low altitude and expect not to overspeed is very strange to me, checklist or no checklist.

I think they were too busy fighting the controls to worry about that.

[acqq]

They followed Boeing instructions (provided in the report, Appendix 2, and also here: https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA... ).

Note IAS DISAGREE alert:

"In the event of an uncommanded horizontal stabilizer trim movement, combined with any of the following potential effects or indications resulting from an erroneous Angle of Attack (AOA) input, the flight crew must comply with the Runaway Stabilizer procedure in the Operating Procedures chapter of this manual:

- Continuous or intermittent stick shaker on the affected side only.

- Minimum speed bar (red and black) on the affected side only.

- Increasing nose down control forces.

- IAS DISAGREE alert.

- ALT DISAGREE alert.

- AOA DISAGREE alert (if the option is installed)"

About which was written here:

https://leehamnews.com/2019/04/03/et302-used-the-cut-out-swi...

"the high speeds observed" ... "were logical. It’s a consequence of following the Emergency checklist for “IAS disagree” (IAS is Indicated Airspeed, i.e. the dynamic air pressure experienced by the aircraft) after takeoff."

In short, seeing that Boeing indeed wrote about the IAS alert being activated when the sensor fails, and MCAS gets activated, I can only conclude that Boeing indeed knew that the pilots would make the plane uncontrollable if they followed Boeing's instructions. It seems they just gambled on the chance that the second crash won't happen so soon after the first.

Either that, or we'd have to believe that what a single pilot manage to do for his Youtube video a company which is to deliver the planes in worth of hundreds of billions (!) of USD wasn't able to do.

[wazoox]

Part of the procedure is to keep thrust or augment it, after disengaging auto-throttle. Remember that they were in stall warning, too (stick shaker), which certainly shouldn't incite anyone to throttle down.

[msbarnett]

Setting it to climb is literally a memory item, pictured here: https://aviation.stackexchange.com/questions/24739/what-is-t.... That’s pitch 5 degrees up, thrust at climb at their altitude.

Why? Because your instruments disagree about your airspeed. You want to have a large margin to keep your speed high enough that you won’t accidentally stall while you try to establish what’s reliable.

[VBprogrammer]

Sure, and you then hold that until the aircraft stalls at 45000ft? Of course not.

You can't point at a memory item and treat it like the pilots can only apply what's in there in exclusion to everything else. The structural limits of the aircraft are there for a reason.

Aside from anything else the pilots were trying to maintain altitude by their communication with ATC.

Not that I'm blaming them. I think they had too much going on to even consider moving the throttles, and thats 100% on Beoing, but it probably didn't help their chances of recovery.

[cjbprime]

I think they couldn't turn the trim wheel because STAB TRIM CUTOUT unpowers it.

[msbarnett]

No, the wheel has an extendable crank handle and is meant for manual use precisely when the electronic stabilizer trim is cutout.

But aerodynamic forces can conspire to make it very hard or physically impossible for human force to rotate it if the elevator is being used to combat the stabilizer at high speeds. See here for more discussion of the physics behind it: https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-ra...

[cjbprime]

Thanks, that makes sense. When the report says that the pilots found manual trim impossible after STAB TRIM CUTOUT, do you think it's referring to an attempt at manual electric trim (expected to fail) or both pilots manually moving the trim wheels with the handle?

[msbarnett]

My (non-expert) reading is that the co-pilot couldn't move the wheel, while the pilot was engaged in fighting to to keep the stick pulled back (a Swedish pilot tried this scenario in a simulator last week and literally had to keep both arms locked around the stick towards the end).

Counter-intuitively, letting go of the stick in brief increments might have been the correct move. Letting the nose pitch down would take force off the jackscrew and let both pilots crank hard on the stabilizer. Boeing manuals once covered this, but apparently they haven't since the 1980s, and their directive after the Lion Air accident made no mention of the necessity of such a procedure. Also they were only 7,000 feet above the ground so whether or not they'd have recovered in time is hard to say. Quite possibly the MCAS had already doomed the flight.

[cjbprime]

> they were only 7,000 feet above the ground

No, it's worse: the origin airport is at 7000ft elevation. They only had around 1000ft height AGL for all of the flight. So I agree that releasing the elevator at all seems surely suicidal.

[msbarnett]

They're at 12,000-14,000 feet altitude at 05:43ish, when the co-pilot reports the non-functional manual trim. So ~6,000-7,000 height.

Still damn close to the ground to be comfortable letting the plane dive.

[phire]

The flight data graph shows no manual electric trim inputs at that time.

So must be manual trim wheel movements.

[WalterBright]

The trim wheel is mechanically connected via cables to turn the jackscrew.

[Rooster61]

It cuts out any electronic input, namely autopilot influence and the electric trim control present on the yoke. The trim wheel is not electric, and is the intended control when electric stabilizer control is either unavailable or intentionally disabled.