[WalterBright]

I know, sounds too simple to be true. But it is:

Boeing Emergency Airworthiness Directive

"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...

This AD was sent to all MAX flight crews. It works because the first incident of MCAS failure (Lion Air) was safely dealt with by doing just this.

[inferiorhuman]

I know, sounds too simple to be true. But it is

No, it's not.

So here's some context. Boeing installed known not-to-spec structural components on the NG. Boeing installed known to fail prematurely slat tracks on the NG and 737 MAX. Boeing installed (probably known) not-to-spec pickle forks in the NG and 737 MAX. Boeing falsified repair documentation for an Air Canada 787. Oh, and of course, Boeing hid any mention of MCAS. Point being Boeing doesn't have a lot of credibility left.

With that in mind:

Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT.

As the Ethiopian crew found out: it can't. The larger instruments of the NG required the hand cranks to shrink while the stabilizer itself grew. With the resulting lower mechanical advantage and increase in force required to move the stab itself the wheels became unusable. Sure, the Ethiopian crew went over the "maximum" speed but they were still under the max diving speed (Vd). That means the cranks were supposed to work.

It works because the first incident of MCAS failure (Lion Air) was safely dealt with by doing just this.

It worked because the first crew got lucky and had a third set of eyes that was free to dig through everything in search of a best guess.

[WalterBright]

> As the Ethiopian crew found out: it can't.

Whatever you read about that is simply wrong. (I've seen a LOT of misinformation in popular print about this.) You're correct that the hand cranks were unusable. But the electric thumb switches WERE usable and were pointed out in the AD.

Note that the crews of BOTH the LA and EA crashes had already used the thumb switches to restore normal trim, the LA crew did so 25 times.

> best guess

No guessing required. Follow the training, which is supposed to be a "memory item", meaning they weren't supposed to need to consult a checklist nor dig through anything nor guess.

I am not a pilot, but I would not consider myself fit to fly unless I knew by memory what every single switch in the cockpit does, ESPECIALLY the ones prominently located within easy reach. You can bet it's not the infotainment system.

For damn sure I would read every Emergency Airworthiness Directive for the airplane I'm the pilot of, most especially one issued in response to a crash.

[inferiorhuman]

Whatever you read about that is simply wrong. (I've seen a LOT of misinformation in popular print about this.) You're correct that the hand cranks were unusable. But the electric thumb switches WERE usable and were pointed out in the AD.

And if you enable the electric trim switches on a 737 MAX you get MCAS activation. MCAS, of course, trims faster than the switches. Using the electric switches is fighting a losing battle (look at the graphs of trim input vs output). How are you supposed to fly the plane when you can't trim the stabilizer?

Look at the graphs from the Indonesian report. The pilots were countering with trim up button presses and MCAS still managed to take the trim to a severe AND position.

Look at the graphs from the Ethiopian report. You'll see a long gap where the electric trim was disabled (leaving the pilots with no way to trim the stabilizer). Outside that gap you'll see an automatic (MCAS) AND command with no change in trim and a couple ANU clicks from the pilots with no resulting change in trim.

No guessing required. Follow the training, which is supposed to be a "memory item", meaning they weren't supposed to need to consult a checklist nor dig through anything nor guess.

And what memory items were they supposed to have in mind? Keeping in mind MCAS presented counter to how Boeing defines runaway trim.

[WalterBright]

> And if you enable the electric trim switches on a 737 MAX you get MCAS activation.

The electric trim switches override MCAS. That is why the steps are:

1. use the electric trim switches to set the trim to normal

2. cut off the electric trim

That's all there is to it.

> MCAS presented counter to how Boeing defines runaway trim.

That's simply false. (And runaway trim does not need definition, Boeing does not define it.)

[inferiorhuman]

The electric trim switches override MCAS.

They pause MCAS but do not disable or override it it. The trim switches move the stabilizer slower than MCAS activation thus as seen by the Ethiopian and Lion Air crews using the electric trim switches is tantamount to fighting a losing batle.

1. use the electric trim switches to set the trim to normal

What happens when the electric trim switches don't work? They didn't in the Ethiopian crash.

runaway trim does not need definition, Boeing does not define it.

Sure they do, it's in the QRH plain as day.

Condition: Uncommanded stabilizer trim movement occurs continuously.

MCAS activation isn't continuous, especially not if you're pausing it with the trim switches.

[bumby]

The problem with this standpoint is that procedural fixes are the least preferable way of managing a hazardous condition. Engineering the hazard away is almost always the better option with procedural mitigation’s being a last resort. If engineering fixes were available and unused its indicative of poor safety engineering practices

[WalterBright]

> The problem with this standpoint is that procedural fixes are the least preferable way of managing a hazardous condition.

The way to make things safe is to address ALL points in the zipper that led to the accident. That includes the pilot error aspects.

[inferiorhuman]

The way to make things safe is to address ALL points in the zipper that led to the accident. That includes the pilot error aspects.

So how do you propose training against an unfinished product? Boeing still hasn't given the FAA a completed software package to evaluate. At the time of the 737 MAX crashes there were, what? two? 737 MAX simulators, and none of them emulated MCAS or even the forces required to crank the stabilizer manually.

One Lion Air flight got lucky because they had a third set of eyes that could spend time going through reams of documentation.

To even begin discussing pilot "error" is disingenuous when the pilots weren't informed or trained on new 737 MAX behavior. MCAS activation is not, and was not, a runaway stabilizer situation.

[WalterBright]

> MCAS activation is not, and was not, a runaway stabilizer situation.

It presented as a runaway stab trim. Repeatedly coming on and driving the nose down is runaway trim. No two ways about it. And the usual, standard, runaway trim procedure would stop it.

> they had a third set of eyes that could spend time going through reams of documentation

From my reading of that incident, nothing of the sort happened. The 3rd pilot simply reached forward and flipped off the cutoff switches. The crew landed safely and went on with their day. Nobody bothered to inform the next crew flying that same airplane.

[inferiorhuman]

It presented as a runaway stab trim. Repeatedly coming on and driving the nose down is runaway trim. No two ways about it.

No, it didn't. From the latest QRH:

Condition: Uncommanded stabilizer trim movement occurs continuously.

Well that's not met as MCAS doesn't run continuously. By design it stops periodically. Put it another way. You're arguing semantics while the 737 MAX remains a smoldering pile of aluminum and hubris.

2.) Control airplane pitch attitude manually with control column and main electric trim as required.

4.) If the runaway stops after the autopilot is disengaged ....

MCAS also stops after the trim switches are hit. So, again MCAS activation is not a runaway trim condition.

From my reading of that incident, nothing of the sort happened. The 3rd pilot simply reached forward and flipped off the cutoff switches.

Reread the report. The third pilot went back into the cabin to fetch reading material.

[WalterBright]

> You're arguing semantics

Trying to argue that the trim system erratically coming on and driving the nose down is not "runaway trim" is arguing semantics. Runaway trim is when the trim is doing something dangerous without command from the pilot.

If the cockpit voice recorder reveals them discussing the definition of "runaway trim" and deciding that the instructions Boeing provided didn't apply, I'd be surprised and interested.

> MCAS also stops after the trim switches are hit.

Exactly, the trim switches override the MCAS. That's why you use the trim switches to set it back to normal, then hit the cutoff switches. That's what the Emergency Airworthiness Directive says to do.

> Reread the report.

I haven't read that anywhere. I don't know what report that is. Reference, please.

[bumby]

I don’t disagree but there are clear hierarchical criteria on how these hazards should be addressed. The reason behind engineering mitigation being favored is because they make the less reliable procedural mitigations moot (I.e., they improve the overall reliability by removing one of the points of failure, in this case the pilot). Forgoing engineering mitigations in favor of procedural fixes goes against good engineering practice at best and is a cheap, lazy fix at worst.

I can understand if the AD was intended as a short term fix but I would question the rationale if it were considered a long term solution

[WalterBright]

> I can understand if the AD was intended as a short term fix but I would question the rationale if it were considered a long term solution

It was not, Boeing at the time was working on a solution.

Regardless, however, the pilots MUST know how to deal with runaway trim. This was true before MCAS, and is true after. It was true on the 757 (I spend 3 years working on the design of the 757 stab trim system). The cutoff switches are prominently within easy reach on the center console for very good reason, 40 years before MCAS.

It is not acceptable that pilots were unaware of the cutoff switches. It is unacceptable that MAX pilots did not read, understand, and remember the Airworthiness Directive sent to all MAX crews.

Similarly, airplane engineers work hard to keep the airplane from catching fire. But pilots also MUST learn to properly use the airplane's fire suppression systems. Most of pilot training consists of learning emergency procedures.

It's why airplanes still have pilots, instead of using automation instead.

Boeing still deserves blame for the flawed MCAS implementation. But there were other contributing factors in the crashes that must be dealt with.

[inferiorhuman]

It is not acceptable that pilots were unaware of the cutoff switches. It is unacceptable that MAX pilots did not read, understand, and remember the Airworthiness Directive sent to all MAX crews.

The Ethiopian crew tried the cutout switches and found they couldn't trim the airplane with the hand cranks because Boeing lied. How is that a pilot training issue?

But there were other contributing factors in the crashes that must be dealt with.

A Boeing employee concern trolling over pilot training is pretty rich considering that Boeing knowingly hid crucial details from pilots.

[WalterBright]

> The Ethiopian crew tried the cutout switches and found they couldn't trim the airplane with the hand cranks because Boeing lied. How is that a pilot training issue?

The Emergency Airworthiness Directive to all MAX crews says:

"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...

> A Boeing employee

I left Boeing about 40 years ago.

[bumby]

I don’t think we disagree on any of the above.

But there were other contributing factors in the crashes that must be dealt with

I don’t necessarily disagree with this either, but it does come across as if we’re being distracted by proximate causes rather than focusing on the root cause. To someone on the outside, it sure seems like there are deeper engineering and cultural problems that deserve a greater priority at this point. Not to belabor the point, but simply issuing a procedural AD doesn’t appear to address the root causes and should just be a stop gap measure

[WalterBright]

It wasn't a "procedural" AD, it was an "EMERGENCY" AD. It says so right at the top:

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

Put another way, would you want to board an airplane where the pilot did not take EMERGENCY instructions seriously? I wouldn't.

> distracted

Pretty much 100% of the popular media (and its repeated appearances on HN) has been on the MCAS design shortcomings. Which distract from dealing with the other causes of the accidents.

As I mentioned previously, the AD was issued as a stopgap measure while Boeing worked on an MCAS fix.