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American Airlines Is Quietly Bringing Back the 737Max

zdnet.com

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Re: American Airlines Is Quietly Bringing Back the 737Max

#191

Post by nl »

atharris wrote: post #91
bronson wrote: post #61

Earlier quoted context omitted.

The MD-11 that was so crashy that airlines eventually sold their airframes to freight companies because cargo can’t refuse to get on one?

I don't think the flight safety record of the MD-11 bears that out[0] - most crashes of significance were either cargo flights (which are much more prone to dynamical issues than passenger flights) or flights in conditions that exceeded design specs (landing in typhoons). It sounds like most airlines sold it because it missed range/fuel burn targets, not because of safety issues. [0] https://en.wikipedia.org/wiki/McD…

My Dad was a frequent business traveller in the 1980s and 90's and I remember him commenting on the MD-11 and saying that he hated them because they were noisy and had lot of vibrations at the back from the center engine.

He said that was the the reason airlines switched to using them as cargo planes.

I realise this is just an anecdote, though.

Re: American Airlines Is Quietly Bringing Back the 737Max

#192

Post by wahern »

harshreality wrote: post #184
knaq wrote: post #115

Earlier quoted context omitted.

It sure looks defective to me: It was controlled more by pressure than movement, using joysticks instead of the traditional huge yoke. When one person was screwing up, the other could not observe this. On a Boeing, each person would feel the other person's force because the controls are physically linked. The stall warning was designed for mild stalls, not severe stalls, and would turn off if the stall was really bad…

The difference between the Boeing problem, where the computer would do un-intuitive things that caused the planes to dive, and the AF447 A330 situation, where the pitot tubes froze over (they shouldn't have) but the aircraft wouldn't try to crash itself, is significant. Of course the pitots shouldn't have frozen over, and of course the stall warnings were poorly thought out, and of course the lack of direct awareness…

It seems like the difference here is that in the Boeing incidents the flight computer was Bonin, inputting the grossly wrong control[1] based on a tragically flawed model of the current angle of attack. Among all Airbus pilots, there are probably only a small number of Bonins. On the Boeing 737-MAX, every plane has a Bonin.

[1] Not just the wrong command, but of a magnitude that greatly exacerbated the situation, based on an unwarranted level of certitude.

Re: American Airlines Is Quietly Bringing Back the 737Max

#193

Post by kjaftaedi »

wycy wrote: post #67

I still don't think I'd trust it. While it's probably true that they fixed the software to never again produce this kind of error, I don't like the idea of software being used to correct the fundamental physics that the airframe is dynamically unstable. While the software probably does a good job of correcting it under a wide range of normal operating conditions, can it deal with evolving or abnormal operating condit…

I was under the impression that this was never a software problem, just that they are attempting to fix the problem with software.

If you get a faulty AoA sensor, or maintenance installs it poorly, there is nothing the software can do to fix that.

The problem was dual AoA sensors were sold as an additional feature instead of a base requirement.

Since the problem was not caused by software, the best you can do with software is to try and build some workarounds.

I think the only way to fix this with software would be to use the other AoA sensor from the secondary MCAS, making the backup system no longer fully redundant, but that's just a guess.

Would be interested in feedback if this is accurate.

At any rate, the software will never be 100%. The biggest change in regards to safety is that pilots are now aware they can turn the MCAS off. Which is the necessary knowledge that would have prevented both crashes.

Re: American Airlines Is Quietly Bringing Back the 737Max

#194

Post by cpgxiii »

bruckie wrote: post #180
cpgxiii wrote: post #33

Earlier quoted context omitted.

No it is not. No regulators has yet been prepared to certify a fixed-wing aircraft that is intrinsically unstable, even after decades of proven fly-by-wire development. The 737 Max has different yoke force during pitch-up than predecessor 737 models, such that at higher angles of attack it does not natively require increasing yoke force to continue to pitch up. That doesn't mean it would pitch up uncontrollably. MCAS…

https://en.wikipedia.org/wiki/Relaxed_stability#Unstable_air... indicates that the MD-11 (which regulators certified) is aerodynamically unstable. (That plane has a compensation system, similar to the 737-MAX.) Is "intrinsically unstable" different from "relaxed stability" in some subtle way? And while military planes are quite different from commercial planes, many (most at this point?) military jets are aerodynamic…

There are different kinds of "relaxed stability", largely depending on which axes of the aircraft are affected, and the magnitude of the instability.

Longitudinal stability is something of a special case, in that essentially all swept-wing aircraft are vulnerable to "Dutch roll" instability and are generally fitted with yaw dampers. Since such stabilizers are, practically-speaking, omnipresent, regulators are OK with using them in what is now a well-understood domain. While it can be unpleasant, all of these aircraft can be flown with a failed yaw damper - notably the 707 family has a particular proclivity for yaw instability, and while almost all civilian users opted for the yaw damper, the largest fleet user, the USAF, did not fit their KC-135s with dampers until well into their service life.

For good reason, pitch instability is a much more serious issue, and there has been very little interest in trying to bring to market a transport aircraft that required active pitch stabilization. Many, if not all, modern clean-sheet airliner designs are fly-by-wire due the the safety, performance, and efficiency improvements to be had, but they are all safely flyable in an "alternate law" (or equivalent) fallback mode.

Combat aircraft, generally speaking, aren't certified aircraft (they have no need be), for good reason - if you're flying a modern fighter and the FBW computers die on you, it's over, you eject. Understandably, that's not an option in a transport aircraft.

Re: American Airlines Is Quietly Bringing Back the 737Max

#195

Post by renox »

stouset wrote: post #165
getpost wrote: post #161

Earlier quoted context omitted.

Mechanically linking is heavier than fbw/electrical/fiber optic linking, and what's the point if there's no mechanical linkage to the control surfaces? With the fbw system, the software makes the choice on how to interpret the control movement, use one or both? If one, which one? EDIT: Maybe you mean that a mechanical linkage would provide a feedback mechanism, so that one pilot would know if the other pilot was atte…

> what's the point if there's no mechanical linkage to the control surfaces? In this case, the pilot would have realized the junior copilot was issuing control inputs and (likely) prevented a plane from crashing, saving the lives of all aboard. Seems like a pretty decent point to me. > EDIT: Maybe you mean that a mechanical linkage would provide a feedback mechanism, so that one pilot would know if the other pilot wa…

Which is one of the main cause of the crash.. Is there an alarm now indicating conflicting inputs from pilots on Airbuses?

Re: American Airlines Is Quietly Bringing Back the 737Max

#197

Post by imtringued »

temp667 wrote: post #137
js2 wrote: post #92

Earlier quoted context omitted.

I’m not a pilot. I’ve just read the Wikipedia page on this crash and the final report. I don’t know what is common or expected and planned for but I take your characterization to mean that you think that it’s not a significant problem. There’s three pitot tubes. There were ADs issued over them icing over. Airbus replaced them multiple times with tubes from different vendors. In the final report, the first major issue…

It really highlights how terribly trained the pilots involved are - temporary inconsistency in measured speeds (there are still plenty of reasonable speed sources) in almost all other planes does not result in the plane crashing. Heck, my GPS can do groundspeed easily enough and you have basic pitch and power settings. How did they not notice their altitude was climbing as they pulled the plane up - they got into a C…

I'm not sure what accident you are talking about but the MCAS in the 737 Max overrode pilot input. The real problem was that pilots did not know that the MCAS existed, nor did they know how to disable it.

Re: American Airlines Is Quietly Bringing Back the 737Max

#198

Post by imtringued »

phkahler wrote: post #186
atharris wrote: post #87

Earlier quoted context omitted.

Ah - I didn't say Boeing's ability to write and test that control software was particularly good (in fact, I think their current track record says exactly the opposite.) I just hate when non-domain experts make judgements about things being 'fundamentally flawed.' Insufficiently tested and documented? Sure. Bad UI/UX? Most definitely. Irredeemable 'because of aerodynamics' according to some private pilot that flew a…

>> because of aerodynamics But yes. MCAS was put in place due to concerns over aero. If that was just to avoid the need for extra pilot training then it should have been scrapped since new training will be required now anyway. But since great effort has been made to fix MCAS we can conclude that the root problem is aerodynamic. Can aerodynamic issues be compensated for with software? Sure. I need to read up on the fi…

You're completely ignoring that flying the 737 MAX without MCAS is not an automatic death sentence. Meanwhile a malfunctioning MCAS is actually an automatic death sentence.

The big flaws are in the software, not in the hardware. So stop focusing on that.

Re: American Airlines Is Quietly Bringing Back the 737Max

#199

Post by imtringued »

jellicle wrote: post #14
ConceitedCode wrote: post #5

Earlier quoted context omitted.

Just curious, what would it take for you to get on a 737-Max? European and American regulators have gone over it with a fine tooth comb at this point and allow it to fly. There is always gonna be people that will say the plane shouldn't fly. Arguably the amount of attention this plane has gotten will probably make it one of the safest in the industry going forward.

I suppose it boils down to whether you have confidence in the FAA of 2020 to make a decision that would be strongly against the financial interests of Boeing and many US carriers. I think the Max will crash again. Excuse me, the 737-8 will crash again.

If pilots can disable the malfunctioning MCAS during emergencies then this type of accident won't happen again. The 737 max might suffer from more emergency landings than usual though.

Re: American Airlines Is Quietly Bringing Back the 737Max

#200

Post by holler »

larrik wrote: post #70
Schiendelman wrote: post #44

Earlier quoted context omitted.

It’s not clear that’s true. Flying doesn’t appear to be causing covid to spread.

Anecdote! One of my co-workers appears to have gotten covid from flying.

They could have got it just as easy at the store before or after the flight, in the airport, or in the uber. Hard to know... Certainly possible but having flown a few times this past year, not too worried.
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