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Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

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Re: Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

#31

Post by geocrasher »

andy_ppp wrote: post #16
geocrasher wrote: post #15

Earlier quoted context omitted.

MCAS was only installed to cover up aerodynamic changes (not flaws) that would have required greater recertification and retraining of pilots. To save that expense, they covered it up with MCAS so they could say "See, it's just another 737!" which caused all the issues we know so much about.

So you’re saying without MCAS the plane flys just as safely but differently which would have required retraining. That’s interesting, thanks!

Yes @andy_ppp that's what I'm saying :)

Re: Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

#32

Post by redis_mlc »

cratermoon wrote: post #19
andy_ppp wrote: post #16

Earlier quoted context omitted.

So you’re saying without MCAS the plane flys just as safely but differently which would have required retraining. That’s interesting, thanks!

No, the plane does not fly safely without MCAS. Without the MCAS there the aircraft has a tendency to pitch up, resulting in a stall situation.

> Without the MCAS there the aircraft has a tendency to pitch up, resulting in a stall situation.

That's not why MCAS was added. Airliners have certification requirements for "flying qualities" (smoothness) as a passenger and IFR platform.

Without MCAS, the 787 MAX pitch-up in some cases exceeded the certification requirements, so MCAS was added to control the rate of pitch-up.

Source: commercially-rated pilot.

Re: Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

#33

Post by manigandham »

cratermoon wrote: post #19
andy_ppp wrote: post #16

Earlier quoted context omitted.

So you’re saying without MCAS the plane flys just as safely but differently which would have required retraining. That’s interesting, thanks!

No, the plane does not fly safely without MCAS. Without the MCAS there the aircraft has a tendency to pitch up, resulting in a stall situation.

That's incorrect. All planes have a relationship with thrust and pitch based on multiple factors (size, weight, speed, wing configuration, altitude, etc). The aircraft was perfectly sound.

The problem was software designed to alter the flight profile automatically to minimize the differences and new training required (and was allowed to override manual inputs). Any pilot with full training of this specific plane without MCAS would have no problem flying it.

The planes didn't crash because they pitched up but because bad software mistakenly, and forcibly, pitched them down.

Re: Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

#34

Post by phire »

geocrasher wrote: post #3

"- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS." Indeed. This was a part failing on an aircraft in flight. It landed without incident, and was likely never in any sort of danger. Losing electric trim is an annoyance but also trims…

Not just the autopilot, but if pitch trim has failed then the Speed Trim System is disabled too.

What is Speed Trim? Well imagine MCAS, but instead of moving the stabiliser near the edge of the flight envelope, it moves the stabiliser all the time (when the speed is below mach 0.68). And instead of being introduced with the 737 Max, it was introduced 35 years ago with the 737 classic.

At least it's mentioned in the manual.

Re: Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

#35

Post by scrollaway »

airhead969 wrote: post #30
i_work_at_GOOG wrote: post #9

Guys, this is a very common and well-known problem. It's been around for over 4 years now. The good news is that instead of nosediving into the ground the 737s can now land and be swapped out. The main take away here is that there are no more fatal crashes. This is a solid improvement for Boeing.

I wonder if people realize it's sarcasm. Nope. - Poe's law

How about scrollaway's law of post quality: if your sarcastic post sounds believable enough for Poe's law, it's a shitty post no matter how it's interpreted.

Re: Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

#36

Post by geocrasher »

na85 wrote: post #27
geocrasher wrote: post #23

Earlier quoted context omitted.

I respectfully disagree. A news article calling them flaws does not make them a flaw. Here's the issue: At lower speeds such as you'd see during a landing approach, the throttle setting of the 737 Max directly affects its pitch. If the pilot were to suddenly reduce throttle, the nose would pitch up. This is due to the engine's more forward position. The forward position of the engines was done so that they wouldn't h…

>At lower speeds such as you'd see during a landing a approach, the throttle setting of the 737 Max directly affects its pitch. Any conventional airliner has this "flaw". If you are at low airspeed and you push the throttles forward, an A320 will exhibit nose-up pitch, too. It's a direct consequence of having giant engines slung kinda-sorta-underneath the wings of a low-wing monoplane.

That's my point. The engine positioning is not an aerodynamic flaw, it's just a design change that makes the aircraft behave differently than the 737-shaped planes that came before it.

Re: Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

#37

Post by cratermoon »

geocrasher wrote: post #24
cratermoon wrote: post #19

Earlier quoted context omitted.

No, the plane does not fly safely without MCAS. Without the MCAS there the aircraft has a tendency to pitch up, resulting in a stall situation.

LOTS of aircraft have a tendency to pitch up or down based on throttle. This isn't unique to the 737 MAX. A quick google on "thrust line pitch moment" gave me this: https://www.homebuiltairplanes.com/forums/threads/thrust-ang... " I want to adjust the thrust angle from where it was (0° with respect to the chord line) to reduce the downward pitching moment when thrust is added (or more importantly the upward pitch mom…

Not many passenger aircraft have a tendency to pitch up to the point of stalling, though.

Re: Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

#38

Post by slacktide »

berkut wrote: post #26
geocrasher wrote: post #3

"- A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS." Indeed. This was a part failing on an aircraft in flight. It landed without incident, and was likely never in any sort of danger. Losing electric trim is an annoyance but also trims…

With respect to the 737-8 MAX though, although in this case it's nothing to do with MCAS, doesn't the 737-8 MAX have smaller radius trim wheels than previous models (so less leverage)? So in theory, trimming might be more difficult on the MAX than previous 737 models, especially at higher speeds (where there's more force on the control surfaces that would need to be counteracted in the case of runaway trim).

The trim wheel on the 737 MAX is identical, down to the part number, to the trim wheel on the 737 NG, which has been in service since 1997. The trim wheel on the 737 NG was reduced in diameter by approx 1/8 of an inch compared to the 737 Classic, which has been in service since 1982, in order to give adequate clearance to the “new” CDU (data entry keyboard for the flight management system). Since the trim wheel is around 10” in diameter, a 1/8” change would have a negligible effect on trim forces.

Re: Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

#39

Post by airhead969 »

worker767424 wrote: post #28
airhead969 wrote: post #21

Earlier quoted context omitted.

I have no opinion about flying on this particular plane. It's not so much MCAS, electric trim, this, or that. The bigger issue is it's too complicated, has too many features, and the FAA can't adequately oversee testing and certification all the way down the engineering stack. Furthermore, because of pressures to save a buck, Boeing is willing to cut corners and sacrifice safety by slapping a plane together without p…

This is every commercial plane, though. We've traded more frequent crashes due to human error for fewer, more spectacular crashes due to how complex planes have become.

False equivalency and hasty generalization that equivocates every plane as having the same risks when they clearly don't, and ignoring testing and training process improvements. Also, an oversimplification that somehow fundamentals of aviation are shifted as a finite resource over to automation when that's clearly not the case.

737 classics are simpler and reliable.

The NG's randomly have hidden structural weaknesses exposed during runway overruns and hard landings when the fuselage breaks up because of Ducommun and Boeing negligence.

The MAX is a steaming pile that may be a white elephant around Boeing's neck.

The 787 is notoriously-bad.

The 777 is pretty good.

Airbus has had much more automation for years. Are they dropping out of the sky? Maybe they manage their complexity better than Boeing, who hires underpaid engineers to work on things that they're really not qualified to do.

Re: Incident: American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure

#40

Post by mypalmike »

na85 wrote: post #20
eric4smith wrote: post #13

I sympathize with the engineers there. It's like a bug that will not go away in some software. You think you've fixed it and all seems well and you get a good nights sleep with the gleam of satisfaction in your eyes. But the next day your manager says "That bug is still there". You incredulously do not believe that bug report and go to replicate it yourself. And surely, under some edge weird case scenario, it really…

Aerospace engineer here. From TFA: >A component of the main electric trim system became inoperative. Our pilots ran the appropriate checklist, which included manually trimming the aircraft. They returned to MIA and landed uneventfully. The issue was not related to MCAS. That statement is from the airline, not from Boeing, so I'm more inclined to trust it. Additionally, if the airline lies and it turns up on an airwor…

These common imperceptible failures... Do they involve the aircraft turning around and flying an hour back to the departure airport?
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