What really happened aboard Air France 447 • Hacker News Board

Re: What really happened aboard Air France 447

#151

Post by gnaffle » Thu, Dec 08, 2011, 9:40 AM UTC

StavrosK wrote: post #142

einhverfr wrote: post #128

Earlier quoted context omitted.

IANA Pilot. I do make aerodynamically correct fixed-wing and lifting-body type paper airplanes, however, and I have had a LOT of fun playing with aerodynamics in this hobby. One thing to keep in mind regaring stall is that it's 100% dependent on angle of attack, not speed (something Popular Mechanics gets entirely wrong). What happens basically is that at a high angle of attack the air layer doesn't track the wing su…

Is it possible that the warning speaker was broken? It's odd that none of the pilots would even acknowledge it. Or does the recorder record the stall warning noise too?

From what I read from the preliminary report, it's established that the stall warning sounded. If it had not been audible on the CVR, they would probably have noted it.

One problem was that the stall warning stopped due to high angle of attack even though the plane was stalled, and it started again when the nose was lowered and the AOA was in the "valid" region again. This might have confused the pilots in a situation when they already had inconsistent airspeeds etc. to deal with.

Re: What really happened aboard Air France 447

#152

Post by furyg3 » Thu, Dec 08, 2011, 9:43 AM UTC

bambax wrote: post #118

Klinky wrote: post #30

Co-pilot Robert, after finally getting full control back from Co-pilot Bonin: "Damn it, we're going to crash... This can't be happening!" Co-pilot Bonin, who had been pulling back & stalling the plane during the crisis: "But what's happening?" Pretty much sums it up. I am thinking that perhaps Bonin had shellshock & may not have even realized he was holding the stick back. Perhaps the more experienced Robert didn't t…

> Add a display that shows the current positions of both control sticks Yes! From the article: " As the plane approaches 10,000 feet, Robert tries to take back the controls, and pushes forward on the stick, but the plane is in "dual input" mode, and so the system averages his inputs with those of Bonin, who continues to pull back. If this is true, it's insane. What does it mean to "average" the inputs of both pilots…

I was shocked that new airplanes use joysticks are just simple inputs and don't give (some) feedback on the current state of the current control surfaces or the state of the other joystick.

This seems like a "feature" of analog controls that you'd want to take forward to fly-by-wire systems.

Re: What really happened aboard Air France 447

#153

Post by Too » Thu, Dec 08, 2011, 9:48 AM UTC

greiskul wrote: post #14

jeffbarr wrote: post #7

Earlier quoted context omitted.

According to the article, the input from the two joysticks is averaged.

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

I guess it could be a cheap workaround to always get smooth transitions when changing pilot. Imagine if one pilot holds full left and the other full right and you press a "switch now!"-button. You would need some kind of transition-period of maybe a second to avoid jerk which could be confusing for the pilot to not know when he has full control and when he is in transition.

Re: What really happened aboard Air France 447

#154

Post by StavrosK » Thu, Dec 08, 2011, 9:54 AM UTC

gnaffle wrote: post #151

StavrosK wrote: post #142

Earlier quoted context omitted.

Is it possible that the warning speaker was broken? It's odd that none of the pilots would even acknowledge it. Or does the recorder record the stall warning noise too?

From what I read from the preliminary report, it's established that the stall warning sounded. If it had not been audible on the CVR, they would probably have noted it. One problem was that the stall warning stopped due to high angle of attack even though the plane was stalled, and it started again when the nose was lowered and the AOA was in the "valid" region again. This might have confused the pilots in a situatio…

Ah, yes, I read that too. It was so frustrating that the pilot kept pulling up all the time, it makes no sense. You'd think that at some point he'd stop and reassess, but I guess he was too confused and shocked to do it...

Re: What really happened aboard Air France 447

#155

Post by DanBC » Thu, Dec 08, 2011, 9:54 AM UTC

teyc wrote: post #102

The state of UX design has advanced so much, perhaps we need more UX testing so that even pilots who are unfamiliar with a plane could figure out what to do. Amazon probably does more with figuring how to help users checkout their shopping cart than plane designers helping pilots get a plane out of a stall. Alternate law and normal law introduces two modes. This breaks one of the rules of user experience, especially…

> The voice should demonstrate increased tension and panic as counting down.

This part doesn't sound so useful, in a cockpit with worried pilots.

Re: What really happened aboard Air France 447

#156

Post by Too » Thu, Dec 08, 2011, 9:58 AM UTC

cellularmitosis wrote: post #72

kmort wrote: post #9

Earlier quoted context omitted.

The author did touch on it: "According to Camilleri, not one of US Airway's 17 Airbus 330s has ever been in alternate law. Therefore, Bonin may have assumed that the stall warning was spurious because he didn't realize that the plane could remove its own restrictions against stalling and, indeed, had done so."

So, here's the problem with this whole normal law / alternate law situation: If a pilot believes he is in normal law, and wants to ascend above the storm, he'll probably just pull all the way back on the stick, thinking "this will cause the computer to ascend as quickly as it can without stalling". AAAARGGHH!!!! This maddening concept of normal law is turning the above insanity into the EXPECTED OUTCOME! Having a com…

This is not only a case of getting comfortable with electronic help. It is also a case of having experience with the extreme conditions in the first place.

I've seen many people who has driven cars, without traction control, for many years and then experience ice for the first time. When the car doesn't move they press the accelerator or turn the steering wheel even more which is the exact opposite of what you should do.

Re: What really happened aboard Air France 447

#157

Post by gnaffle » Thu, Dec 08, 2011, 9:58 AM UTC

jarek wrote: post #75

jrockway wrote: post #69

Earlier quoted context omitted.

There is other debris that can clog pitot tubes. Birgenair Flight 301 crashed because some wasps built a nest in a pitot tube during an extended layover: http://en.wikipedia.org/wiki/Birgenair_Flight_301 189 people died. (Also note the failure to react properly to the stall warnings. This comes up again and again.)

I wonder if in a couple of decades we'll look back at pitot tubes and wonder what the hell we were thinking using such a fragile solution. (Of course, in a couple of decades we'll probably have a much more accurate external method of finding out speed/airspeed.)

Maybe, but keep in mind that they are in operation on thousands of planes operating night and day, and they very seldom fail. So it's not what you would call a fragile solution. After all, the pitots involved in this flight were already due to be replaced because of icing problems.

Re: What really happened aboard Air France 447

#158

Post by Simon_M » Thu, Dec 08, 2011, 10:00 AM UTC

nikcub wrote: post #110

bhickey wrote: post #68

Earlier quoted context omitted.

The NTSB concluded that 990 was a homicide. A relief pilot assumed control after take-off and then deliberately crashed the aircraft. From what I hear, it wasn't a fun week at the RI Medical Examiner's office.

the other similar incidents are Birgenair Flight 301, where the pitot tubes were blocked because of insect nests, resulting in pilot confusion: http://en.wikipedia.org/wiki/Birgenair_Flight_301 and Aeroperu Flight 603, where the pitot tubes had been covered by maintenance workers and not removed prior to takeoff, also resulting in pilot confusion and lack of confidence in instrument readings: http://en.wikipedia.org/…

Considering how many incidents there seems to be due to the loss of these airspeed sensors it seems crazy not to have an additional, different method of calculating airspeed.

Is there a reason GPS is not suitable here?

Re: What really happened aboard Air France 447

#159

Post by Angostura » Thu, Dec 08, 2011, 10:03 AM UTC

acabal wrote: post #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.

I couldn't actually bring myself to click to page 2.

Re: What really happened aboard Air France 447

#160

Post by einhverfr » Thu, Dec 08, 2011, 10:03 AM UTC

bambax wrote: post #146

einhverfr wrote: post #128

Earlier quoted context omitted.

IANA Pilot. I do make aerodynamically correct fixed-wing and lifting-body type paper airplanes, however, and I have had a LOT of fun playing with aerodynamics in this hobby. One thing to keep in mind regaring stall is that it's 100% dependent on angle of attack, not speed (something Popular Mechanics gets entirely wrong). What happens basically is that at a high angle of attack the air layer doesn't track the wing su…

A commenter below (cellularmitosis) makes a very interesting point: Bonin may not have realized he was in "alternate law" (let's call it "mode" instead of "law"). In "normal mode" the computer will not let pilots stall the plane, whatever they do; it will accept the commands up to what it considers dangerous. There's an "envelope" of acceptable plane movements; pilots can move inside this envelope but not outside of…

yeah, I agree with that. Also there's another factor in that stall warnings may have been seen as an ADIRU malfunction rather than an actual stall. In those cases, I suppose pulling back might make some sense if you think you have bad ADIRU input and the plane is in normal law.