Runaway Stabilizer!! How to stop MCAS.
Runaway Stabilizer!! How to stop MCAS. on HackerTube: recommended by 7 Hacker News commenters across 3 separate months, 2019–2022.
A Boeing 737 pilot explains the runaway stabilizer checklist, the procedure for stopping unwanted horizontal stabilizer movement such as an MCAS activation on the 737 MAX. He walks through the steps, the trim cutout switches and the jackscrew mechanism, and shows a simulator run including the manual trim wheel effort.
What HN commenters said
13 Hacker News comments link this video. Each one links back to its thread.
ZancariusMay 2019Strongly recommends
Depends on the aircraft. Some modern jetliners are using fly-by-wire, while others have hydraulically-boosted controls. Some still rely on cable-and-pulley. Either way, as I understand, it wouldn't matter with the MCAS-related MAX aircraft crashes. The elevator trim is able to move the entire elevator (literally, the entire elevator moves in response to the jackscrew controlled by the trim system) to such an extent that, depending on CG, airspeed, and other factors, it cannot be overpowered by moving the control surface to its full deflection. So whether or not the MAX had boosted controls or fly-by-wire probably wouldn't have mattered in the case the aircraft were trimmed fully nose-down. The pilots would have been struggling to maintain control either way. That's why there's stabilizer trim cut-out switches and manual trim. I'd highly recommend Mentour Pilot's videos on the subject, links below: Runaway Stabilizer: How to stop MCAS - ▶ this video Boeing 737 Unable to Trim! Cockpit video (full flight sim) - [link] Five questions about the Boeing 737 MAX Answered - [link]
in “Long Before Boeing 737 Max Crash, Ethiopian Air Pilot Warned of Dangers” · View on HN
pasApr 2019Strongly recommends
> You probably have nothing to worry about with air travel. Well, the conclusion is already made in the statistics, and air travel is the safest, yes, but it's worrying that it's safe despite the enormous fallacies, despite the insane pressure of market forces. A very eye-opening thing is to watch what the pilots should have done: ▶ this video Runaway stabilizer scenario has associated memory items (meaning the pilot must have the checklist committed to memory). There are big wheels that turn, with noise and a big visibility marking. This was Boeing's initial defense too, that the pilots fucked up, because disabling any electronics works the same way. (There's a cutoff switch.) So if something is doing something, shut off the power, rotate the wheels manually. And in this regard Boeing is right. Pilots decisionmaking was suboptimal. However, it is Boeing's fault that they opted for a no-training-required strategy. A similar WTF is that pilots don't keep up with the aviation industry news. How - the fuck - can you pilot a plane that you know nothing about (except that your license is valid for it)!?
in ““I worked at Boeing for about 1.5 years in the 2008-9 time period”” · View on HN
exabrialMar 2019Strongly recommends
I highly recommend everyone suggestion engineering solutions to watch this video from an actual pilot performing a runaway stabilizer procedure in a 737 simulator. ▶ this video What happened is a series of failures; this video frames it perfectly.
in “Where Boeing’s 737 Max Planes Go When They’re Grounded” · View on HN
DeclanomousMar 2019Strongly recommends
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] ▶ this video
in “No call for simulators in new Boeing 737 Max training proposals” · View on HN
janocMay 2019Recommends
Well, the "Stabilizer wheel - grasp and hold" item of the procedure doesn't necessarily mean the crew will be able to override it. That's the last ditch option on the checklist, when everything else has failed, even turning the motors off (there could be e.g. a short circuit powering the motor). There is no clutch on the 737, AFAIK, because the forces are such that it wouldn't work. Here is a good video by an actual 737 captain explaining how the runaway stab trim procedure works and what you have to do. ▶ this video And this simulator video shows both how the 737 horizontal stabilizer is controlled and what kind of forces are on the trim wheel and control column when severely out of trim: [link] Should give you an idea what were the Ethiopian pilots facing when unable to use the electric trim, plane trimmed nose heavy by MCAS and at high speed ...
in “Ethiopian Max Crash Simulator Scenario Stuns Pilots” · View on HN
sundvorApr 2019Recommends
Not that video, but at least it shows the automatic trim system in action - and is rather educational: [link] . Even better: ▶ this video
in “Ethiopian Airlines Boeing 737 pilots 'could not stop nosedive'” · View on HN
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proctorApr 2019Recommends
this video[0] from "mentour pilot" on youtube explains the stabilizer system quite well. it seems the trim wheels are connected manually to the trim mechanism in the back, but when the trim stabilizers are in an extreme position the wind loading on them makes it very hard/impossible to rotate the trim wheels manually. from what i understand, one way to relieve/lessen the wind loading so that the manual wheels can be used again is to (in the case of trim down) dive the plane. this would lessen the wind loading on the stabilizer and allow the manual wheels to move again. but you would need "room" to dive, something they did not have in this case. [0] ▶ this video
in “Ethiopian Airlines 737 MAX Investigation Preliminary Report” · View on HN
dhxFeb 2022Cites it
The difficulty of using the manual trim wheels is also demonstrated in this simulator run showing the MCAS problem: ▶ this video There is some discussion amongst pilots at [link] which further explains how difficult it can be to manually reduce load on the stabilizer and manually trim the nose up.
in “How the Boeing 737 Max disaster looks to a software developer (2019)” · View on HN
morganwAug 2020Cites it
Watch how much effort it takes to adjust trim with the motors disabled ▶ this video It's good that MCAS will now disable itself without having to disable the trim motors completely. I wish they'd just taken the hit on a new type rating and given up on MCAS completely after the failures. Perhaps new 737 pilots could get training on NG and MAX at the same time? One thing I'm not seeing much discussion of today (though it was addressed in previous posts about the MAX) is the development process issues that led to the problems in the first place. Some blame it on post-McDonnell-Douglas-merger penny-pinching, non-engineer-indulging managers. Whatever it was, the investigation should have resulted in not just plane modifications, but company ones.
in “U.S. FAA proposes requiring key Boeing 737 MAX design changes” · View on HN
weaksauceApr 2019Cites it
They had 40 seconds to avert the accident from what I read. the memory items for runaway trim take about 1 minute in a relatively calm simulator with a professional 37 pilot to get to that point where they flip the switch[0]. They still had an incorrectly trimmed aircraft when they got to that point. also of note was that the pilots in the sim were at 3000' AGL where the other ones that crashed were at about 1000' AGL. 0. ▶ this video
in “Boeing delays 737 MAX software fix delivery” · View on HN
AserApr 2019Cites it
The pilots were trained on how to deal with a runaway trim stabiliser. The procedure hasn't changed from the old 737, the only thing that has changed is that it is that the failure mode is more likely to occurr on the 737 MAX. From the article: “A properly trained pilot should be able to solve an MCAS anomaly or any uncommanded flight-control input through procedures that are taught to all 737 pilots,” said Menza, noting that the emergency information Boeing distributed in December reiterated those procedures. Here's a video of a competent 737 pilot showing those exact procedures: ▶ this video Obviously the MCAS system is badly designed, but any automation system can fail and pilots need to know how to deal with it.
in “Lack of redundancies on Boeing 737 MAX baffles some involved in developing it” · View on HN
js2Apr 2019Cites it
It’s a lot of cranking to do by hand[1]. You could use the electric trim to reset back to zero and then disable electric trim. (But, that isn’t the procedure.) 1. ▶ this video
in “Ethiopian Pilots Followed Boeing’s Required Steps to Disable 737 Max System” · View on HN
morganwApr 2019Cites it
After watching Mentour Pilot's demo correcting for runaway trim in a 737 simulator, it seems like a switch that cuts out computer (autopilot, auto-speed, MCAS) control of the elevator trim motors, but keeps the column switches working would be nice. Consider how cumbersome & slow the manual wheels are: ▶ this video It would be one more layer of complexity, but perhaps when the column trim switches are operated, all computer control could stop until it (autopilot, etc) is re-enabled by a human. The cutout switches in the center are still there if two column switches short out (used to be a single up-down switch, but it was single point of failure to runaway so now there are separate enable and direction switches).
in “Boeing software under scrutiny as Ethiopia prepares crash report” · View on HN