mhandley

52 ms·

601.
by mhandley 8y ago
Indeed looks like they did disable MCAS using the stabilizer trim cutout switches, but the aircraft was trimmed nose down when they did so. Aerodynamic loading prevented manual trimming using the trim wheels. They eventually turned electri
602.
Ethiopian 737 Max: Aircraft Accident Investigation Preliminary Report [pdf](ecaa.gov.et)
57 points by mhandley 8y ago|2 comments
603.
by mhandley 8y ago
Trim is much more important in a large jet than it is in a Cessna because of the speed range it operates over. At lower speeds with flaps up, you need a high angle of attack to maintain altitude. This entails a very high stick load in a m
604.
by mhandley 8y ago
The original article title is somewhat less clickbait: "Introducing a More Seamless Navigate on Autopilot"
605.
by mhandley 8y ago
The bad AoA probe can cause IAS disagree, according to the FAA Emergency Airworthyness Directive: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/... Take a look at the graphs from the LionAir crash:
606.
by mhandley 8y ago
The preliminary report is not yet public - Ethiopian have seen it, hence their press release, and some of the media have been briefed on its contents, hence the BBC article, but it's not yet public.
607.
by mhandley 8y ago
From today's Ethiopian Airlines press release: "The preliminary report clearly showed that the Ethiopian Airlines Pilots who were commanding FlightET 302/10 March have followed the Boeing recommended and FAA approved emergenc
608.
by mhandley 8y ago
There's no trim tab on a 737 - the whole horizontal stabilizer is moved to trim the aircraft in pitch. Normally this is done electrically, but the stabilizer jackscrew can also be moved using manual trimwheels that move the jackscrew
609.
by mhandley 8y ago
The 737 is still mostly 1960s technology, despite all the tweaks over the years. With autopilot off, autothrottle off, and electric trim disabled, which is the situation the Ethopian pilots would have ended up in from following the checkli
610.
by mhandley 8y ago
The speculation is that his employer, which flies a lot of 737s, didn't like him using a company simulator to illustrate a safety issue with the 737.
611.
by mhandley 8y ago
This was posted on PPrune: "Originally Posted by infrequentflyer789 Since this video may not be coming back I'll post a sort of transcript from memory since I was lucky enough to get to watch it. I'll try and just describe wh
612.
by mhandley 8y ago
Will be interesting to see the details when the report is actually public. It does sound like the scenario that Mentourpilot explored in the simulator is close to what happened, namely: Bad AoA probe causes MCAS to trim down, and also to i
613.
by mhandley 8y ago
Extract from the Ethiopian Airlines press release: "The preliminary report clearly showed that the Ethiopian Airlines Pilots who were commanding FlightET 302/10 March have followed the Boeing recommended and FAA approved emergency
614.
Ethiopian crash: Preliminary report says pilots followed Boeing's guidance(cbsnews.com)
2 points by mhandley 8y ago|0 comments
615.
by mhandley 8y ago
I agree that on the NG, IAS disagree and an uncommanded stabilizer trim are much less likely to occur together. But if you did have an uncommanded nose-down trim close to the ground, you still wouldn't want to reduce throttle because
616.
by mhandley 8y ago
The cutoff switches actually disconnect the power to the trim motor, so this is unlikely unless Boeing changed something else they've told no-one about. More likely is that the pilots turned the electric trim back on because as the air
617.
by mhandley 8y ago
I'm not trying to excuse Boeing's shoddy implementation of MCAS, nor their hiding its existence from pilots - both of those are inexcusable in my opinion. But my understanding is that when working properly, MCAS would not kick in
618.
by mhandley 8y ago
The 737 Max is not actually unstable without MCAS. The requirement is for increasing angles of attack to require increasing back pressure on the yoke up until the edge of the flight envelope. The lift from the larger nacelles placed furth
619.
by mhandley 8y ago
Now there's a blast from the past. As a young researcher, I got to have a Sparcbook circa 1994 to take to events and demo the multicast multimedia conferencing software we were working on. It cost about five times more than everythin
620.
by mhandley 8y ago
I think that would open up a different safety issue. Suppose you're in a tight turn for some reason, pulling back hard on the yoke, as you have to do in a tight turn. The aircraft is at fairly high angle of attack, but not yet quite
621.
by mhandley 8y ago
Yes. But the AoA disagree indicator did not disable MCAS. In similar circumstances, SouthWest pilots would not have taken off, because AoA disagree would have indicated as soon as they'd begun their takeoff roll. But if an AoA sens
622.
by mhandley 8y ago
The full preliminary report from the LionAir crash is here: https://www.flightradar24.com/blog/wp-content/uploads/2018/1... I've put the relevant figure showing the trim adjustments here: http:&#x2
623.
by mhandley 8y ago
Agreed. Boeing's revised MCAS will disable itself if the AoA sensors disagree by more than 5.5 degrees when MCAS activates, or a sustained difference of more than 10 degrees otherwise. This is to take into account the fact that the s
624.
by mhandley 8y ago
All 737s have two AoA sensors - they're used for several purposes, not just MCAS. Originally MCAS used only one of the two sensors, though it alternated which one with each flight. The optional features were an AoA disagree indicator
625.
by mhandley 8y ago
Because if you did that, you'd have to alert the pilots when the AoA sensors disagree and MCAS has been disabled. And you can't do that without training them on what that means, notably how the plane will now fly differently with
626.
by mhandley 8y ago
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 somethin
627.
by mhandley 8y ago
The official preliminary report is due out in a day or two, but the contents have already started to leak: https://www.cnbc.com/2019/03/29/ethiopian-crash-boeing-737-m...
628.
by mhandley 8y ago
All 737s have two AoA sensors. The left one feeds the left air data computer and the right one feeds the right air data computer. The AoA disagree indicator displays when the two disagree, but is optional and was not fitted on the planes
629.
by mhandley 8y ago
An AoA disagree indicator was an option. But it was never an option for this to disable MCAS, as this would have resulted in a change of the flight characteristics that would have required training.
630.
by mhandley 8y ago
They did increase the length of the nose landing gear, which helped a bit. But increasing the length of the main landing gear would have required moving the gear further outboard, as there was no space to extend the gear in an inboard dire

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