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

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

#61

Post by _ph_ » Wed, Mar 31, 2021, 6:07 AM UTC

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…

No, to expertise. An Aerospace engineer is more qualified to correctly interpret the event report and whether this is a common problem or something related to the previous problems of that model.

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

#62

Post by danaliv » Wed, Mar 31, 2021, 6:08 AM UTC

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…

Flight instructor here. This person knows what they're talking about.

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

#63

Post by slacktide » Wed, Mar 31, 2021, 6:09 AM UTC

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…

Everything you said is false.

The 737 MAX is not unstable, even with MCAS inoperative, and does not have a tendency to pitch up if trim fails or MCAS is inoperative.

Source: EASA 737 MAX Return To Service report, top of page 6.

https://www.easa.europa.eu/sites/default/files/dfu/B737_Max_...

The trim wheel on the 737 MAX is exactly the same as the trim wheel on the 737 NG. They have the same part number.

Source: my own two eyes and a 12” Mitutoyo caliper. The 737 Classic trim wheel (pre-1997) is approx 1/8” smaller than the NG and MAX trim wheel.

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

#64

Post by danaliv » Wed, Mar 31, 2021, 6:12 AM UTC

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?

Even gliders have trim. It's not technically considered a primary flight control because you can survive without it, but at the very least it's annoying not to have it.

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

#65

Post by conistonwater » Wed, Mar 31, 2021, 6:12 AM UTC

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?

One "silly" reason why minor failures result in flying back to the original airport is sometimes that the original airport is some sort of hub for the airline with plenty of equipment and personnel for maintenance, which makes it cheaper for the airline to repair the plane specifically there compared to another airport. If you follow avherald.com even a little bit, you will notice a lot of incidents result in exactly that.

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

#66

Post by spoonjim » Wed, Mar 31, 2021, 6:13 AM UTC

sneak wrote: post #11

benmarten wrote: post #6

I'm refusing to fly the MAX, period! The plane is flawed by design...

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.

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

#67

Post by spoonjim » Wed, Mar 31, 2021, 6:14 AM UTC

technick wrote: post #43

I flew on one of the returned 737-max aircraft down to Houston about a month ago. Flight was uneventful and landed a few minutes early.

Thankfully, our standards for aviation safety are not low enough for an anecdote of a safe landing to be a valuable data point.

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

#68

Post by salawat » Wed, Mar 31, 2021, 6:15 AM UTC

manigandham wrote: post #33

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.

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 with…

What the poster was more likely referring to was the uncertifiable behavior that would occur without MCAS during a wind-up turm or during descent whereby stick control forces would slacken on the way to stall instead of requiring steadily increasing pressure on the control column to bring the plane to a stall due to extra lift from the forward nacelles. While technically a pilot could deal with it, aircraft that demonstrate said behavior cannot be certified as civil transport aircraft without appropriate mitigations.

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

#69

Post by Toutouxc » Wed, Mar 31, 2021, 6:16 AM UTC

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.

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 positively stable airplane, just like basically all civilian aircraft. If the trim on such plane fails (gets stuck), it becomes annoying to fly, like a car that pulls to one direction. It doesn't do anything violent or sudden (the plane is trimmed correctly until the last moment) and it's possible to overcome the force with the control column and return safely.

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

#70

Post by koonsolo » Wed, Mar 31, 2021, 6:21 AM UTC

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.

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.