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What really happened aboard Air France 447

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Re: What really happened aboard Air France 447

#41
post #19

Earlier quoted context omitted.

Which raises a very good question, when would you ever want that joystick behaviour?

This is a fantastic question. I can think of no situation where this behavior would be desireable, but then again IANAP

I'm a pilot and that seems insane.

Re: What really happened aboard Air France 447

#42
post #40

Earlier quoted context omitted.

Making a computer that can fly without airspeed makes less sense to me than making an airspeed sensor that either doesn't ice, or can de-ice itself. Is that so impossible?

Supposedly they do de-ice themselves, but that obv didn't work properly here.

According to the article, the pitots did, in fact, de-ice and return to normal functioning. However, apparently the alternate law needs to be manually reset, since the plane remained in direct input mode, and thus the pilots managed to stall the plane even though its instruments had all recovered.

Re: What really happened aboard Air France 447

#43
post #40

Earlier quoted context omitted.

Making a computer that can fly without airspeed makes less sense to me than making an airspeed sensor that either doesn't ice, or can de-ice itself. Is that so impossible?

Supposedly they do de-ice themselves, but that obv didn't work properly here.

Ah, I was not aware they already could. My next question is why not make themselves de-ice better?

This maybe seems trollish or silly, but in all seriousness, if your sensors aren't good enough, first rule out improving the sensors before you try to compensate with the system.

Re: What really happened aboard Air France 447

#44
I don't think the average person realizes that for aircraft pilots ice is a constant worry even in tropical areas of the world.

The temperature drops 1.98C for every 1,000 feet you go up so you can see quite quickly how fast you can enter an area below the freezing point of water.

Icing of the pitot tube and carburetor are a constant worry at least for prop driven aircraft. Right from day one you're taught what to look for signs of carburetor icing and how to correct it. Water in the fuel is probably #3 on the list.

I never got far enough along to learn about wing icing I ran out of money for lessons but really everyday it's ice, ice, ice!

Re: What really happened aboard Air France 447

#45

Could they not simply have looked out the window and understood? Or simply felt gravity in their bodies? A 40 degree incline is pretty severe, wouldn't it be obvious?

Our bodies are horrible when it comes to spatial awareness.

Pilots are trained to ignore sensory input like the feel of gravity, the feel of being in a dive/climb/bank and use the instruments to make determinations about what the aircraft is doing. Usually those feelings are dead wrong.

It's amazing how flying into a cloud bank, even though you've been flying straight and level, suddenly your body screams at you that you're in a descending bank or something. You just learn to disregard those senses and trust the instruments.

As far as looking out the window, it was cloudy, at night, and at high altitude. At high altitude in straight and level flight your nose is pointed at blue sky, not the visual horizon.

Re: What really happened aboard Air France 447

#46

Could they not simply have looked out the window and understood? Or simply felt gravity in their bodies? A 40 degree incline is pretty severe, wouldn't it be obvious?

In the dark, in a storm, you have no reference points. In a moving plane, your reference frame is further confusing. There are stories of pilots making a nice, 1-g bank turning the craft upside down and not noticing until it was too late due to white-out conditions. Gravity is only one of the forces acting on the pilots' bodies.

Re: What really happened aboard Air France 447

#47
post #45

Could they not simply have looked out the window and understood? Or simply felt gravity in their bodies? A 40 degree incline is pretty severe, wouldn't it be obvious?

Our bodies are horrible when it comes to spatial awareness. Pilots are trained to ignore sensory input like the feel of gravity, the feel of being in a dive/climb/bank and use the instruments to make determinations about what the aircraft is doing. Usually those feelings are dead wrong. It's amazing how flying into a cloud bank, even though you've been flying straight and level, suddenly your body screams at you that…

Ah, that bit about being trained to ignore their body is interesting. I was not aware of that, and it answers my question pretty well.

Re: What really happened aboard Air France 447

#48
That was one of the tensest things I've read in a while. My heart was pumping up until the end. The level of stress, confusion, and terror those pilots, not to mention the passengers, must have experienced must have been truly terrible.

Re: What really happened aboard Air France 447

#49

Could they not simply have looked out the window and understood? Or simply felt gravity in their bodies? A 40 degree incline is pretty severe, wouldn't it be obvious?

The nose was "only" pitched 15 degrees up. The descent was at 40 degrees. With considerable turbulence, and a storm raging outside even the rapid descent may not have been apparent (body-wise).

Re: What really happened aboard Air France 447

#50

I've followed the discussion of the AF447 investigation on several flight discussion forums. The PF (Bonin) apparently never became aware of his angle of attack (once the airplane fully stalled, AOA was absurdly high). He did not seem to be aware that his constant inputs had caused the Airbus's THS (trimmable horizontal stabilizer, horizontal flaps on the tail) to deflect to maximum in order to try to keep the nose u…

You suggest that one problem might be that Bonin didn't know his angle of attack. Alternately, I remember a similarity here with an Egypt Air flight that went down when some instruments went dead: when one of the instruments experienced malfunction, the pilots suddenly found it hard to believe anything the computer was saying. So maybe, on some level, Bonin dismissed the stall warning because the speed sensor had failed. One sensor is faulty, he might have reasoned, how can I know the computer isn't just over-reacting to that?
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