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0 pointsummonk4y ago0 comments

The Ethiopian Airlines pilots followed the EAD to the letter.

First, they attempted to adjust trim using electric stabilizer trim, and then upon realizing that the they were experiencing an uncommanded nose down stabilizer trim, they followed the runaway stabilizer procedure - namely, stab trim cutout and trim wheel grasp and hold. Afterwards, they attempted to adjust the stabilizer manually.

There is a note in the EAD that electric stabilizer trim can be used to neutralize the stabilizers before doing a stab trim cutout, but crucially Boeing did not instruct pilots to make sure to neutralize trim first using electric trim before doing the stab trim cutout.

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6 comments · 2 top-level

whoknowswhat114y ago· 2 in thread

Is this a joke?

ERROR: Literally the first paragraph of the EAD is about controlling airspeed. [Edit: This is not correct]

They hit 700(!!) MPH. They literally commanded full take off power to accelerate the plane into the ground. You can add power if your pitch is high to arrest a sink rate (ie, during landing), but if you are pitched down, you pull power.

There is also a 300 second limit on T/O power - I'd be interested if they exceeded that as well.

The maintenance on this plane was terrible.

This was not a situation where folks involved "did everything right".

For those not familiar, approx 3 minutes after they did a stab trim cutout they put stab trim back to normal. That's never been in any guidance for EAD or runaway.

The 4th activation of MCAS moved trim down (to 1 unit, should have probably been at 4.3 - 5.x or so). That probably doomed them.

ummonkOP4y ago

The first paragraph of the EAD is:

"Disengage autopilot and control airplane pitch attitude with control column and main electric trim as required. If relaxing the column causes the trim to move, set stabilizer trim switches to CUTOUT. If runaway continues, hold the stabilizer trim wheel against rotation and trim the airplane manually."

WalterBright4y ago

The entire EAD must be read, not the first paragraph. Including the digressions (your phrase). It's only two pages.

I am not a pilot. But I am an aerospace engineer who worked on critical flight detail designs. You've likely flown on my work. My father was a pilot for the AF for 20 years. You don't get to be an old pilot if you don't pay attention 100% to the instructions and training. Flying isn't like driving a car. Humans are not natural flyers. You rarely get a second chance if you make a mistake flying.

Maybe 90% of flight training is dealing with emergencies. If you're not dedicated to doing it right, and doing it 100%, every time, you've got no business being a pilot with hundreds of lives depending on you.

P.S. I've gone flying with pilot friends many times. I watch them do the preflight. If they're not 100% perfect with it, I'm getting off.

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WalterBright4y ago· 2 in thread

> Boeing did not instruct pilots to make sure to neutralize trim first using electric trim before doing the stab trim cutout.

Yes, they did:

"Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT."

https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA...

Note also that the EA pilots had already successfully overridden and restored normal trim twice with the electric trim switches.

(I added the emphasis on "before".)

ummonkOP4y ago

That's not an instruction - it's a digression. The wording there is "can be used".

The actual instruction is to follow the AFM Runaway Stabilizer procedure. That's exactly what the Ethiopian Airlines pilots did.

WalterBright4y ago

> That's not an instruction - it's a digression. The wording there is "can be used".

Why do you think Boeing wrote an EMERGENCY AIRWORTHINESS DIRECTIVE and the FAA mandated it be sent to all MAX pilots?

If you're a pilot, it is YOUR JOB to read, understand, and remember every EMERGENCY AIRWORTHINESS DIRECTIVE. Not to parse words. If you want to parse words, get a job as a lawyer, not a pilot.

The "can be used" is there to explain how to overcome aerodynamic forces that make using the manual trim wheel difficult.

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6 comments · 2 top-level

whoknowswhat114y ago· 2 in thread

Is this a joke?

ERROR: Literally the first paragraph of the EAD is about controlling airspeed. [Edit: This is not correct]

There is also a 300 second limit on T/O power - I'd be interested if they exceeded that as well.

The maintenance on this plane was terrible.

This was not a situation where folks involved "did everything right".

For those not familiar, approx 3 minutes after they did a stab trim cutout they put stab trim back to normal. That's never been in any guidance for EAD or runaway.

The 4th activation of MCAS moved trim down (to 1 unit, should have probably been at 4.3 - 5.x or so). That probably doomed them.

ummonkOP4y ago

The first paragraph of the EAD is:

WalterBright4y ago

The entire EAD must be read, not the first paragraph. Including the digressions (your phrase). It's only two pages.

P.S. I've gone flying with pilot friends many times. I watch them do the preflight. If they're not 100% perfect with it, I'm getting off.

1 more reply

WalterBright4y ago· 2 in thread

> Boeing did not instruct pilots to make sure to neutralize trim first using electric trim before doing the stab trim cutout.

Yes, they did:

https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA...

Note also that the EA pilots had already successfully overridden and restored normal trim twice with the electric trim switches.

(I added the emphasis on "before".)

ummonkOP4y ago

That's not an instruction - it's a digression. The wording there is "can be used".

The actual instruction is to follow the AFM Runaway Stabilizer procedure. That's exactly what the Ethiopian Airlines pilots did.

WalterBright4y ago

> That's not an instruction - it's a digression. The wording there is "can be used".

Why do you think Boeing wrote an EMERGENCY AIRWORTHINESS DIRECTIVE and the FAA mandated it be sent to all MAX pilots?

If you're a pilot, it is YOUR JOB to read, understand, and remember every EMERGENCY AIRWORTHINESS DIRECTIVE. Not to parse words. If you want to parse words, get a job as a lawyer, not a pilot.

The "can be used" is there to explain how to overcome aerodynamic forces that make using the manual trim wheel difficult.

1 more reply

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