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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

#71

Post by ramblerman »

trynton wrote: post #56
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…

It's not the engineers pain, as it wasn't an engineering decision to mount the engines higher and forward of the wing. Precipiting a pronounced nose-up aspect. All the same, I admire your attempt to deflect blame from the management at boeing.

> I admire your attempt to deflect blame from the management at boeing.

Bah, what a vile comment. He didn't contest that at all.

It's the engineers who will have to go through this exercise of fixing it, and he identified something most of us can probably relate to.

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

#72

Post by satellite2 »

manigandham wrote: post #47
cratermoon wrote: post #37

Earlier quoted context omitted.

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

It does not just pitch up randomly. It does pitch more than other 737s due to engine size and placement, but that's just the specific behavior of this plane. Stalls are not a serious problem, they're basically the first thing pilots learn to solve. And there are plenty of aircraft that are more challenging to fly. That's what training is for. The real issue is that pilots should have full understanding of the behavio…

> Stalls are not a serious problem

They account for 25% of fatal accidents [1]

[1] https://www.aopa.org/-/media/Files/AOPA/Home/Pilot-Resources...

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

#73

Post by tallanvor »

mypalmike wrote: post #40
na85 wrote: post #20

Earlier quoted context omitted.

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?

Yes, if the destination isn't a maintenance base that stocks the part that fails. It's happened to me - 45 minutes into a 1 hour flight they decided to turn around and return to our departure airport. It's very annoying.

The problem is that some failures mean the plan can't fly again until the part is replaced, and sometimes it's cheaper to turn around than to have the plan sit idle until they can get the replacement part out to it along with someone certified to repair it.

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

#74

Post by bonzini »

slacktide wrote: post #54
na85 wrote: post #22

Earlier quoted context omitted.

>As I understand it the aircraft has a quite complex relationship with trim because of fundamental aerodynamic flaws (engines are too far forward). That's not really correct. The engines being in a different position means the aircraft doesn't meet a very specific criterion of the FARs (positive stick force gradient). The 737 Max has the exact same relationship with trim as any other airliner. >Am I right in saying o…

One thing that has always bothered me about how MCAS was implemented - if it truly was a stick force gradient issue, why not make the change in the Elevator Differential Feel Computer, which already manipulates the stick force gradient during approach to stall, rather than physically moving a control surface? Aside note, the elevator feel computer is a mechanical / non-electronic computer that is stuffed full of aner…

Maybe that's why, I don't blame engineers who didn't want to touch it...

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

#76

Post by bonzini »

dghlsakjg wrote: post #60
BenoitP wrote: post #50

"- 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." I don't get it. It is common for other airliners to rely systematically on trimming? Do other airliners have similar 'correcting' systems as MCAS?

Almost every airplane except the absolute most basic have trim controls for flight surfaces, especially the elevator. Even little two seat Cessnas get trim controls. Trim is changed for each phase of flight. Electric trim is just a motor spinning the manual trim control. Most airliners will be doing constant trim adjustment. If you want a real change of pace check out Airbus’ control system. It does a lot more interv…

AF447 was definitely pilot error, not realizing that the aircraft was stalling.

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

#77

Post by salawat »

slacktide wrote: post #54
na85 wrote: post #22

Earlier quoted context omitted.

>As I understand it the aircraft has a quite complex relationship with trim because of fundamental aerodynamic flaws (engines are too far forward). That's not really correct. The engines being in a different position means the aircraft doesn't meet a very specific criterion of the FARs (positive stick force gradient). The 737 Max has the exact same relationship with trim as any other airliner. >Am I right in saying o…

One thing that has always bothered me about how MCAS was implemented - if it truly was a stick force gradient issue, why not make the change in the Elevator Differential Feel Computer, which already manipulates the stick force gradient during approach to stall, rather than physically moving a control surface? Aside note, the elevator feel computer is a mechanical / non-electronic computer that is stuffed full of aner…

>Aside note, the elevator feel computer is a mechanical / non-electronic computer that is stuffed full of aneroids and solenoids and cams and followers and servovalves. Straight out of the 1950’s.

That's likely why they didn't. That type of change is hard to conceal and far more difficult to keep out of the documentation. A software change could potentially be handwaved. Full on revamping of said system would probably have edged a regulator enough to have raised an objection or a deeper dive into the nature of the reconfiguration.

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

#78

Post by Closi »

spoonjim wrote: post #66
sneak wrote: post #11

Earlier quoted context omitted.

I have taken a similar stance myself (not that I'm flying anywhere these days) but, out of curiosity: do you also refuse to be a passenger in automobiles? The 737MAX is quite a bit safer than those.

The 737MAX is safer than a car per passenger mile, but saying that it's safer than "driving" is false unless you assume that both trips are the same distance. This isn't usually how it works. A Californian who refuses to vacation in New York to avoid the 737MAX usually does not drive to New York instead -- they drive to Point Reyes or something nearby, or just don't go at all.

This is true to some extent, although the difference in safety is so large that in the example you are still more likely to die from a car accident on your way to Point Reyes than your flight to New York.

Deaths from car accidents per 100 million miles driven: 1.33

Deaths from plane accidents per 100 million miles by plane: 0.0077

(Note above statistics are from the US)

In your example, California to New York would be approx 3k miles while point Reyes is approx 150-300 miles depending on where you start. A 10-20x longer journey via plane is still an order of magnitude safer.

Per mile, the car is about 200x more dangerous - in fact the usual statistic is that getting on a plane is safer than driving to the airport, not doing the whole distance in the car.

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

#79

Post by bonzini »

airhead969 wrote: post #39
worker767424 wrote: post #28

Earlier quoted context omitted.

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…

As a passenger the 787 is a fabulous aircraft.

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

#80

Post by [deleted] »

lisper wrote: post #59
trynton wrote: post #58

Earlier quoted context omitted.

@na85:"Aerospace engineer here." Appealing to authority. > That statement is from the airline, not from Boeing, so I'm more inclined to trust it .. On an unstable aircraft such as the 737 Max, if the trim fails then the nose pitches-up, precipitating a stall, unless the pilot can execute a manual trim. Which is difficult without electrical-power-assist fed to the wheel. As the wheel was made smaller to allow for bigg…

> Appealing to authority. No. He is an authority. He is providing his bona fides. Not the same thing.

[deleted]
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