Author Topic: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'  (Read 59021 times)

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Offline KL27x

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1150 on: Yesterday at 10:14:02 pm »
^That's another way of saying "unstable."
Unstable doesn't necessarily mean the plane can't be flown without electronic aid, requiring 50 corrections per second. Instability can be slow/gradual.

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The airplane still has positive aerodynamic stability even with MCAS disabled.
The MAX is unstable at higher AOA. It will fly just fine, as long as the pilot keeps one eye on his pitch/AOA while doing w/e else he has to do. When things go wrong, you don't want to have to juggle so many things, and it's during takeoff and landing that you generally have things going wrong and are flying at a high AOA. It would also come into play in bad weather with shifting up/down drafts.

Test pilots complained for reasons. No matter how you want to word it, the plane doesn't behave as well after the modification. "Requiring more corrective force" sounds benign, but the plane can even run out of elevator range (no matter how hard he presses on the stick? Still not enough!) before the pilot realizes it, which is what MCAS is for. MCAS adjusts the stabilizer to get the elevators back into range for condition, but then the hydraulics can become the weak link. The elevator didn't need to do as much in the original design. It didn't have this additional nose up force that appears and gets even stronger at higher AOA.

Ideally, horizontal stabilizer adjustment would be for convenience. It was never meant to be a main maneuvering surface. Once adjusted, the plane should be able to fly to its limits without having to touch it, again. For the MAX, this is apparently not the case. 
« Last Edit: Yesterday at 10:37:08 pm by KL27x »
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1151 on: Yesterday at 10:59:03 pm »
"Instability" might be the wrong word for it - the nacelle's lift and mounting the engine in front of the wing, ahead of the plane's center of gravity -  a positive feedback loop leading to a stall. How bad is it?

Some team at Boeing was in charge of MCAS, identifying the need for it, flew the plane with those settings and changes, and put that behavior into the flight sim, as well as the transgressions.
 

Online sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1152 on: Yesterday at 11:17:13 pm »
The horizontal stab trim is not a “merely for convenience” flight control in an airliner, but is rather a control surface that is trimmed for each substantial airspeed change. (It’s the “raar-raar-raar” spinning crank sound that you hear periodically on every approach as the aircraft slows. You can also sometimes hear it on takeoff and climb out, but there other noises sometimes dominate.)
 

Online sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1153 on: Yesterday at 11:26:34 pm »
^That's another way of saying "unstable."
No, it’s not.

Aerodynamic stability has a defined meaning.

At most, it’s insufficiently positive stable, but it still exhibits positive stability (does not go neutral or negatively stable) throughout its flight envelope.

Quote
The airplane still has positive aerodynamic stability even with MCAS disabled.
The MAX is unstable at higher AOA.
No, it’s not. https://www.quora.com/Is-the-Boeing-737-MAX-aerodynamically-unstable-I-have-read-that-the-new-heavier-and-higher-mounted-engines-have-changed-its-center-of-gravity/answer/Alan-Dicey
 

Offline KL27x

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1154 on: Today at 12:27:10 am »
Apologies for stating opinion like fact. "Lower margin of stability," per the link. But still stable. And with the suggestion that it is perfectly airworthy, EXCEPT that it doesn't meet original cert? Ok, that sounds reasonable.

Per link, the higher the AOA, the more force the pilot has to exert in the original 737 (and is the goal in all planes). But in the MAX the force decreases. According to him, it doesn't increase less. It decreases from the force required at a more moderate AOA.

Unless the pilot has freak proprioception of large muscle groups, he can't tell the exact location of the yoke so much as how much force he is putting on it. In turbulence or extreme corrective maneuvering, it might even be hard to feel if/when the yoke is (net) moving. So while the plane might still be "aerodynamically stable," this is obviously undesirable for any plane, even if it were a new design. IMO.
« Last Edit: Today at 12:55:06 am by KL27x »
 

Online BravoV

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1155 on: Today at 08:46:03 am »
Imo, up to this stage, the only possible to fly is thru political maneuvers and backup by politicians, of course, compromises included ... nasty.  >:D

Unless Boeing turning into non profit organization.  :-DD

You have to factor in Trump's new tariffs on Airbus too, with it's consequential knock on effect on Scotch Whisky exports (Huh?).

https://www.bbc.co.uk/news/uk-scotland-scotland-business-49915034

Afraid those are just precursors, more are coming like a carpet bombing the whole Europe.

Not sure bout you Brits though, assuming once you're detached from EU as in Brexit, the bargaining power will not be as strong as EU as the whole, like below "opinionated" column ...

Read thoroughly here -> China tariff deal was easy compared to the EU’s bazooka-proof trade walls

Ok, enough off topics.  ::)
« Last Edit: Today at 08:51:20 am by BravoV »
 


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