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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

#91

Post by na85 »

trynton wrote: post #58
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…

@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…

>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.

Please educate yourself on the fundamentals. The 737 MAX is not unstable.

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

#92

Post by Toutouxc »

jiofih wrote: post #83
Toutouxc wrote: post #69

Earlier quoted context omitted.

> 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. MCAS is a safety mechanism meant to suppress a very specific behavior in a very specific corner of the flight envelope where an airliner is not supposed to operate at all. Its mere existence doesn't mean that the MAX is an unstable plane. The 737 is still a posi…

An out of whack MCAS that pushes the nose down, to a point where you can’t overcome it with the trim control, technically puts it into the “unstable” category, doesn’t it?

MCAS moves the trim wheel itself, so you don't overcome it with trim, you overcome it with your control column. Also, MCAS moves the trim to an extreme position that is nowhere close to how the plane should be trimmed for normal flight. But the pilots were still able to overcome it with their control columns for quite a long time. A situation like that is usually called a "trim runaway" and it can happen for multiple reasons, MCAS being a rather exotic one, but they all have the same solution, a procedure that the pilots unfortunately weren't able to follow.

The other way the trim can fail is that it gets stuck. When that happens, it usually gets stuck in a reasonable position (because the plane was flying normally before it happened), which makes the flight back annoying and renders systems that rely on trim input, like MCAS, autopilot, Speed Trim, inoperable, but it doesn't make the plane unsafe or uncontrollable.

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

#93

Post by na85 »

mypalmike wrote: post #51
na85 wrote: post #41

Earlier quoted context omitted.

That would strain the definition of "imperceptible", wouldn't it? My point is that aircraft break all the time. Once in a while they break in such a way that they need to return to base. This wasn't an MCAS failure.

Your wording was problematic. "In this case" strongly implied you were putting this incident in the same category.

Perhaps my wording was careless; I can't go back and edit it now.

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

#94

Post by corndoge »

weego wrote: post #87
worker767424 wrote: post #25

Earlier quoted context omitted.

But this doesn't feed the machine that is the 24-hour news cycle. I fully expect cable news to try to declare "more trouble for troubled plane," even though it appears to be a garden variety failure.

I think that attempts to whitewash the fact that Boeing have managed to burn the trust it spent decades building on the space of 2 or 3 years. This is the natural outcome -- until time proves otherwise again, every failure will be under a lens

> until time proves otherwise again, every failure will be under a lens

But it's really not every failure. There were 2 other failures on Boeing airliners yesterday alone and nobody posted the other two.

American B38M near Nassau on Mar 29th 2021, pitch trim issue/failure (OP's article)

Southwest B737 at Denver on Mar 30th 2021, speedbrake arming issue

United B739 at Denver on Mar 30th 2021, flaps problem

Day before

Batik B739 at Semarang on Mar 28th 2021, hydraulic fault

Aeroflot B738 at Krasnodar on Mar 28th 2021, flaps problems

Day before that

ANA B773 over Pacific on Mar 28th 2021, engine shut down in flight

iAero B734 near Evansville on Mar 27th 2021, loss of cabin pressure

Here's a 737-800 with a similar electrical trim issue recently https://www.youtube.com/watch?v=nLonztIXXWQ You probably didn't hear about that one

Like others said these aircraft fail every single day. People who read about them don't post them on HN because they're so common.

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

#95

Post by jacquesm »

trynton wrote: post #58
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…

@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…

FFS. Really. The 737 Max is not an unstable aircraft. Stop repeating this nonsense. I don't know how often I've had to explain this on HN and having to repeat this over and over again gets really tiring. The 737 Max is stable over the whole flight envelope. I'm a lay person when it comes to aircraft (even though I've written software for the aviation industry) but I know enough to know that you haven't a clue. Please don't berate others for being subject experts and disclosing this up front.

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

#96

Post by sofixa »

koonsolo wrote: post #70
trynton wrote: post #56

Earlier quoted context omitted.

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.

It's definitely the engineers pain. It's clear that management is the cause of all this shit, but the problem now lies in the engineers lap. So who has to solve it? Right, the engineers.

They're the ones that accepted and designed an unsafe aircraft ( a single sensor known for failure feeding a critical system that can crash an airplane? And they hid it from the FAA? They absolutely knew what they were doing and should rot in jail for at least a few years).

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

#97

Post by igravious »

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…

FTA: "The issue was not related to MCAS"

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

#98

Post by cryptonym »

Closi wrote: post #78
spoonjim wrote: post #66

Earlier quoted context omitted.

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 b…

What you say is true but coarse statistics doesn't reflect actual situation. You would have to compare 737 MAX deaths per mile to OP car deaths per mile. Maybe taking into account that hopefully OP doesn't speed, drink, text, watch harry potter... Don't know if deaths includes pedestrian or bikes killed by cars, could be irrelevant if you only compare your odds to be alive after journey. I'd also expect a recent car with good safety to have a lower rate than average and maybe 737 MAX higher than average?

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

#99

Post by qwertox »

slacktide wrote: post #44
mypalmike wrote: post #40

Earlier quoted context omitted.

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

Yes, they do. I suggest that you set avherald.com as your homepage for a week, and learn how common air turnbacks and diversions are.

Fun comment section on that site

> This girl is one of a few 757s that Delta uses exclusively for charters. Lower cycles on them. 31.5 years old and still chopping up birds. Love it. Long live the 757!!

http://avherald.com/h?article=4e52aeea&opt=0

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

#100

Post by VBprogrammer »

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…

Where have you been all through the 737 Max debacle! It's refreshing to read someone who genuinely understands this issue.

And for what it's worth I've pondered that before and my only conclusion was as others have said here, probably a lack of detailed organisational knowledge on the design of the pitch feel computer. Perhaps there are confounding factors, it has its own pitot tube but not a AoA vane for example. Or perhaps changing it may have triggered more regulatory oversight than MCAS did (unfortunate given events which followed).

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