[Declanomous]

I'd highly recommend anyone who wants to see what an MCAS runaway looks like and the steps needed to correct it watch the following video by Mentour Pilot.[1] He's a 737 pilot for a European budget carrier, and I believe he is qualified to certify other pilots.

In the video he goes over what an MCAS failure/runaway stabilizer would feel like to the pilots, the troubleshooting steps, and at the end of the video he shows a simulated runaway MCAS failure in a sim.

He also has a few other videos on the MCAS accidents. I'd highly recommend watching all of them; he does a very good job at putting everything into perspective in a way that the news does not.

[1] https://youtu.be/xixM_cwSLcQ

[poof131]

Great video, thanks for sharing. That simulator work at the end was a fantastic demonstration of team work. Crew Resource Management.[1] I still remember DAM CLAS from the Navy.[2] Numerous examples in the video. Sad and terrifying thinking about what it must have been like for the pilots and passengers of the crashed airlines. If the issue was MCAS, the slowly worsening situation, never disabling the trim, just one step to remedy the situation that’s never taken, and the intuitive solution of pulling back hard on the yoke not working, because Boeing removed it in the latest version--a sad example of awful decision making on the ground.[3]

1. https://en.wikipedia.org/wiki/Crew_resource_management

2. https://quizlet.com/45297265/crew-resource-management-crm-th...

3. https://www.seattletimes.com/business/boeing-aerospace/u-s-p...

[VBprogrammer]

I'll need to check for relevant sources, but I'm fairly sure that the idea that boeing removed the "trim brake" is wrong. It's simply that the MCAS doesn't respect it. I think this is consistent with the Speed trim system which may be trimming opposite the pilot in normal operations.

[mhandley]

And the reason MCAS doesn't respect it is because MCAS is designed to activate in high AoA situations. You get into a high AoA situation because you're already pulling back hard on the yoke, likely in an attempt to avoid something bad happening such as avoiding a collision. If MCAS did cutout when the yoke was pulled back hard, it would disable itself at precisely the time it is actually needed. This design decision does make sense. The real problem is not telling the pilots about it.

[dsfyu404ed]

And the obvious solution is "tell pilots about it" which is going to piss off the public because a procedural change (training), a new UI to make it more obvious (like IIRC Southwest implemented) and a minor code fix (comparing the AOA sensors) will not satisfy everyone who's out for blood.

[magduf]

>will not satisfy everyone who's out for blood.

People are right to be out for blood. This mistake cost hundreds of lives, and was clearly a case of criminally negligent behavior.

[Zancarius]

In that video, I think he's primarily talking about handling runaway stabilizer trim. It just so happens that solving runaway stabilizer trim works with MCAS failures which may have been the case with the Lion Air flight the day before the fatal accident. Unfortunately, therein lies the problem: From what I've read, an MCAS failure is different enough from runaway stabilizer trim that it might not be immediately obvious what went wrong before it's too late. Juan Browne[1] discusses this in his latest video on the MAX 8[2]--namely that pilots get so conditioned to hearing the trim wheels operating that they may not notice periodic adjustments by the flight computer when MCAS fails and starts adjusting full nose-down.

(I'm posting this as ancillary information, not to be contrarian! I might be entirely wrong; that was just my interpretation of Mentour Pilot's video. His resources are absolutely fantastic[3], and I think anyone interested in aviation should certainly take a look!)

[1] Juan Browne is a former USAF pilot who's currently an FO on the 777 and has 40 years flying experience. I don't think he has experience with the 737, but I think his coverage is valuable too.

[2] https://www.youtube.com/watch?v=Ora-yZCTtpg

[3] You're absolutely right! Mentour is a training captain on the 737 (737-800, I believe) and oversees certifying new pilots/captains. One of the things I like about him most is that regardless of seniority, he's incredibly humble and has said in earlier videos that he occasionally flies right seat to maintain that skill for training others. Great guy! I really wish more people were like him.

[Declanomous]

I assumed the failure in the simulator was an MCAS failure, but I'm not sure. I think that the MCAS system pauses for 5 seconds every time you hit the trim button, so it kinda seems like it might be MCAS but I have no idea.

The checklist to fix MCAS and runaway trim is supposed to be the same, so I guess the question is whether the trim wheels move in a substantially less noticeable way with an MCAS failure. I certainly can't say.

I could totally see someone hearing the trim wheels running when they are trying to trim out the MCAS adjustments and assuming that the wheel is moving in the opposite direction that it actually is. In a high-stress situation a mistake like that seems incredibly plausible.

[SAI_Peregrinus]

AFAIK in a runaway trim situation the trim wheels move continuously, while in an MCAS activation or in normal operation of the auto-trim systems they move in bursts. The fix is the same, but the recognition is very different.

[WrtCdEvrydy]

> he shows a simulated runaway MCAS failure

'I am not doing that...' is now on my most terrifying phrases to hear.

[Declanomous]

The thing that was the most chilling to me was the fact that the last item on the memory checklist is to try and prevent the trim wheel from moving using physical force. At that point it almost seems like "well, you are probably going to die, but you might as well keep yourself busy in the process."

I thought the communication was really interesting. Air France Flight 447[1] crashed due to the pilot flying pulling back on the stick for over a minute while in a stall, overriding the command inputs of the pilot monitoring. The other pilots realized that the pilot flying had been pulling the stick back the entire time only a few seconds before impact, and at that point it was too late to recover. The transcripts from the cockpit voice recorder are pretty chilling.

That exact situation isn't exactly possible in a Boeing because the sticks are linked, but there were a several crashes in the modern era that occurred because of communication issues in the cockpit. Of course, in addition to better communication, we have systems like MCAS which are designed to prevent pilots from repeating the mistakes of AF447. In this case it obviously didn't work out that well.

[1]https://en.wikipedia.org/wiki/Air_France_Flight_447

[achandlerwhite]

I can’t watch the video at the moment, but I’m of the understanding that the manual wheel actually easily overpowers the electric trim motors—-that it is simple to stop them from spinning and not to difficult to manually spin them as required.

[lultimouomo]

In the video there is a suggestion on how to hold the wheel without breaking your wrist, so I assume it's not too pleasant to do. They also manually spin the wheel and it looks quite hard and slow (the monitoring pilot alone, which is using his left hand, can barely do it; when the flying pilot helps him with his right hand things go better)

[roelschroeven]

I wouldn't say "easily": at some point in the video the guy on the right tries to trim manually but fails -- it only starts working when the guy on the left starts helping him.

[dotancohen]

I doubt that there would ever be need to physically overcome the jackscrew motor (trim motor), as there is an electrical cutout switch in ready reach. The issue the GP discusses is when due to whatever reason the trim runs away (electrical or otherwise), the 737 has two physical wheels that the flight crew can turn, _OR CATCH_ while it is turning. That is like stopping a spinning bicycle wheel by grabbing it. It is physically dangerous to the crew member.