Comment by filleduchaos
3 days ago
What does the AF 449 crash have to do with the existence of a button to return the aircraft to wings level + zero vertical speed?
To answer your question though, LVL has been around for close to two decades now. IIRC there was a Cirrus/Garmin partnership that added it to the latter's G1000/GFC 700 and it's since trickled out to other consumer-grade autopilots.
The AF 449 was in a stall, and the pilots panicked and did exactly the wrong thing. The pilot came out of the lavatory and immediately realized what was wrong, and pushed the stick forward. But it was too late.
If the captain could figure it out, so could the computer.
I recall another crash, not so long ago, of a commuter plane where the wings iced up a bit and the airplane stalled. The crew kept trying to pull the nose up, all the way to the ground. They could have recovered if they pushed the stick forward - failing basic stall recovery training.
There are many others - I've watched every episode of Aviation Disasters. Crew getting spatially disoriented is a common cause of crashes.
No, one of the pilots put the plane into an aerodynamic stall because they had failed sensors giving them erroneous airspeed information and he kept overriding the other pilot who was doing the correct thing to recover from the stall he had put the aircraft in.
What exactly was a computer at the time supposed to figure out with unreliable data, especially after a stall had first developed?
Also in fairness I was a bit too opaque with my point, which is that 1) LVL requires the pilot to actually press it, which they are unlikely to do if like you yourself have mentioned they are clueless about what situation they're actually in, and 2) LVL is not appropriate stall recovery so I don't really see how it is relevant to a case of an aerodynamic stall.
> LVL requires the pilot to actually press it
Of course. I did say it was a button to press!
> LVL is not appropriate stall recovery
It should be. I don't see how it couldn't be designed to do stall recovery. After all, the avionics do recognize a stall (as it activates the "pull up" stick shaker).
"and he kept overriding the other pilot who was doing the correct thing to recover from the stall he had put the aircraft in."
Yep, the real design problem here is the idiocy of allowing dual input.
2 replies →
> a commuter plane where the wings iced up a bit and the airplane stalled. The crew kept trying to pull the nose up, all the way to the ground.
There’s probably a lot that match, but sounds like Colgan Air 3407 in 2009 (the last major commercial airline crash in the US before the mid-air collision earlier this year in DC)
https://en.wikipedia.org/wiki/Colgan_Air_Flight_3407
Yes, that's the one. Nice work finding it!
(It was AF 447.) I take this opportunity to recommend Admiral Cloudberg's excellent analysis (longread): https://admiralcloudberg.medium.com/the-long-way-down-the-cr...
The autopilot had disengaged, most likely because the pitot tubes had iced over.
The aircraft system entered ALT2 mode, where bank-angle protection is lost. Protection for angle-of-attack is also lost when 2 or more input references are lost.
You might describe these circumstances as the computer saying "I don't know what the heck's going on, you humans figure it out please".
As a former engineer who worked on the 757 flight control system, I am not terribly impressed with that design.
Having 3 pitot tubes iced over means they read 0 velocity. It is reasonable for the computer to be designed to recognize that if all three pitot tubes read 0, then the pitot tubes are the problem. With the altimeter unwinding, it should be able to recognize a stall. With the turn and bank indicator, and the AOA indicator, it should be able to return to straight and level.
Recall that the captain figured it out at a glance and knew exactly what to do.
4 replies →