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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

#101

Post by VBprogrammer »

slacktide wrote: post #86
bonzini wrote: post #76

Earlier quoted context omitted.

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

Predicated on their assumption that the flight control laws would prevent a nose-up control input from stalling the aircraft, and not realizing that the aircraft was in alternate law. Some of the last words on the CVR from the pilot flying were “But I’ve been at maxi nose-up for a while” while the computer was shouting STALL STALL STALL in the background.

You ever have the experience when you listen to someone speak with a strong accent, you don't quite catch the beginning of a word and the whole of what they say sounds like a foreign language?

I imagine that is how those poor pilots felt as their instruments screamed conflicting information at them as they tore through the skies above the mid-atlantic.

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

#102

Post by jakeogh »

Toutouxc wrote: post #92
jiofih wrote: post #83

Earlier quoted context omitted.

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…

If I understand correctly, ultimately they could not overcome it, and after many dives, the computer succeeded in crashing the aircraft... it's practically irrelevant long the pilots were able to overcome it.

The base issue is that it was even possible for the control of humans with hundreds of lives in their hands to be overridden by a set of predefined instructions.

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

#103

Post by ergl »

scrollaway wrote: post #35
airhead969 wrote: post #30

Earlier quoted context omitted.

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.

In more profane terms: https://news.ycombinator.com/item?id=17733579

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

#104

Post by tremon »

salawat wrote: post #77
slacktide wrote: post #54

Earlier quoted context omitted.

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 probabl…

A software change could potentially be handwaved

This to me seems a much greater process failure.

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

#105

Post by Toutouxc »

jakeogh wrote: post #102
Toutouxc wrote: post #92

Earlier quoted context omitted.

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…

If I understand correctly, ultimately they could not overcome it, and after many dives, the computer succeeded in crashing the aircraft... it's practically irrelevant long the pilots were able to overcome it. The base issue is that it was even possible for the control of humans with hundreds of lives in their hands to be overridden by a set of predefined instructions.

It's very relevant that the plane was flying long enough for the pilots to go through the runaway trim checklist, which, if they went through the procedure, would have probably saved the plane. They didn't go through the checklist, because AFAIK they didn't realize immediately that it's a runaway trim situation, because of imprecise and/or conflicting indications in the cockpit.

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

#106

Post by argvargc »

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…

All of these statistics are too generalised to be useful.

People who fly in planes are generally not flying from every conceivable location on the globe to every other one in an even distribution and randomly using every type of plane available on every carrier. Neither are those driving cars driving from every possible destination to every other in every kind of vehicle etc.

Compare someone exclusively flying back and forth between one wealthy first world country to another on a Dreamliner run vs someone driving an 80's Ford Pinto regularly across treacherous mountain passes in the Andes.

Or the converse (use your imagination).

An important and useful statistic is that one particular, new model of aircraft is tremendously crashy considering the amount of time it's been in service.

It makes sense to avoid travelling on that aircraft, until it can be proven to have a flight-miles/crash ratio more in line with other models. (Which may take a number of years, or decades, especially if people are avoiding it...)

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

#107

Post by BillyTheKing »

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…

the good old programming testing rule: the number of bugs you will find in a piece of software is proportional to the number of bugs you already found

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

#109

Post by avereveard »

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…

Both incorrect. The stability system to correct pitch to avoid training is only one side of the story. The other side is there wasn't a linear relationship between pitch, aoa and stick forces, and that would not have passed the faa certification.

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

#110

Post by qubit000 »

Boeing has lost the public trust not only in the US, but internationally.

Inherent instability aside, fact remains the general perception is that Boeing retrofitted engines too large for 50yr plane design necessitating structural modifications which compromised its flight worthiness. As a result, software had to be written to compensate for this, which unbelievably, relied on input from a single sensor--iow, single point of failure.

The lost of trust is further exacerbated by the fact that Boeing/FAA knew there was high probability of another crash after the first catastrophic incident but refused to ground the planes continuing to let them fly while issuing deceptive public statements regarding the planes safety.

Boeing's largest market is China, which justifiably, will not allow the 737 to fly within their territory.

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