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What really happened aboard Air France 447

popularmechanics.com

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Re: What really happened aboard Air France 447

#241

Post by einhverfr »

soren_dahl wrote: post #192
bambax wrote: post #146

Earlier quoted context omitted.

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…

There's a school of thought that says that user interfaces should be modeless, I wonder if the concept of a mode here is a fault in the design of the HCI as well as insufficient training?

Actually the normal vs alternate law thing might be a mode to build into the displays. I am usually a modeless fan and a VIM user, but this is an exception ;-)

Re: What really happened aboard Air France 447

#242

Post by freemarketteddy »

barrkel wrote: post #236
freemarketteddy wrote: post #116

Earlier quoted context omitted.

>how does a plane know it's stalling if the pitot tubes are frozen? I think it can easily do that by measuring the G force similar to an accelerometer on iPhone.

Accelerometers measure acceleration. You won't feel any unusual G forces for any constant velocity, whether it's climbing or descending.

Yes you're right...Stall is not a free fall but a sudden reduction in lift which can occur for instance when the angle of attack increases beyond a certain value.

Re: What really happened aboard Air France 447

#243

Post by krschultz »

runningdogx wrote: post #29

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…

I find the fact that the control sticks do not move together the most troubling design flaw. Bonin's actions were not obvious to the other two pilots, if the other pilot saw his stick pulled all the way back when he knows they need to get the nose down and pick up airspeed, he'd instantly know what was wrong. Instead he is looking at instruments and talking to the other pilot and is completely unaware of how self-inflicted the crisis is.

Re: What really happened aboard Air France 447

#244

Post by wavephorm »

mtts wrote: post #181
nikcub wrote: post #86

I simply don't undersand (or don't comprehend) how the pilots don't know these things. My knowledge of planes is 4 hours of pilot lessons and watching a few documentaries on the Discovery channel yet I know that pulling the nose up of a plane would stall, that when you get bad readings from instruments you cross-check, and that a frozen pitot tube giving bad airspeed readings is very likely in high-altitude storms. I…

At night, over an ocean, in a storm, with no visibility, in possibly significant turbulance and responsible for the lives of 300 people. I doubt knowledge acquired from an episode of "Air Crash Investigation" is very useful in such a case. Watching documentaries or looking up stuff on the internet does not make anyone an expert. That Bonin guy, as inexperienced as he was, knows far, far more about piloting airplanes…

  That Bonin guy, as inexperienced as he was, knows far,
  far more about piloting airplanes than you do.
Not anymore.

Re: What really happened aboard Air France 447

#245

Post by Florin_Andrei »

runningdogx wrote: post #29

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…

> without valid airspeed there's a risk of overspeed which can cause a new set of problems

What problems specifically?

> Nobody believed a passenger aircraft would be so stable during a full stall.

What was the plane "supposed" to do during the stall? If you're inside the plane, how does it feel when the plane has stalled?

Re: What really happened aboard Air France 447

#246

Post by teyc »

jrockway wrote: post #232
teyc wrote: post #126

Earlier quoted context omitted.

There's actually a tendency to reduce the number of different alarms and use screen information to indicate the problem Yes, that'd be good UX. There should be only one actionable task presented at any time to correct errors. In any case, user testing is more important than guidelines. I wonder if grouped alarms make any sense. For instance you can group all alarms related to stalling together, and present the one th…

This already happens. I have not been trained to fly an airliner, but I believe that the priority is something like stall, gpws (flying into the ground), tcas (flying into other traffic), master warning, and master caution. These all have their own lights and sounds in the cockpit, and if I know them, so does the flight crew. Presumably the 150 messages that needed to be looked at were all "caution" messages. Too man…

      The plane tried to physically force the
      controls to nose down,
I'm glad you mentioned that. I thought that's what a plane should do at first, and then on second consideration wondered if the psychology of panicking pilots would be to fight the controls in order to wrest the plane from going down.

Re: What really happened aboard Air France 447

#247

Post by Florin_Andrei »

einhverfr wrote: post #128
bambax wrote: post #112

Earlier quoted context omitted.

What's missing from this article is the fact that the Captain chose to fly right into the storm, saying "on va pas se laisser emmerder par des cunimbs" (in essence: "fuck this storm") http://www.lexpress.fr/actualites/2/actualite/des-dialogues-... This is incredible hubris. Then, in the middle of the storm he leaves the two copilots alone, one of them quite inexperienced, and goes for a nap. He's obviously trying to…

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…

> 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 surface properly and so you are deprived of standard lift.

So the air layer on the back "peels off", and you have turbulent flow on the back, instead of laminar, is that right? So the negative pressure is greatly diminished.

Re: What really happened aboard Air France 447

#248

Post by smiler »

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 do wonder if passengers knew what was happening. Many might have been asleep. It sounds like there was a fair bit of turbulence on.

It looks like from the report that none of the cabin crew raised any concerns, so I'm wondering if people were pretty much oblivious and they went quickly.

Re: What really happened aboard Air France 447

#249

Post by Florin_Andrei »

jrockway wrote: post #224
gnaffle wrote: post #167

Earlier quoted context omitted.

Yes, maybe a combination of shock, confusion or distrust in the instruments was a factor. It will be interesting to see what the human factors group of the investigation comes up with. I'm sure that the flight training will also be investigated, there has been concerns that improper stall recovery technique is being taught by some instructors: http://www.caa.co.uk/docs/33/012010.pdf (And of course, in planes that are…

(And of course, in planes that are not certified for stalls, you can't really practice full stalls and have to train on approach to stalls instead.) Of course, very little airliner training happens outside a simulator, which can you can stall without damaging anything.

> Of course, very little airliner training happens outside a simulator, which can you can stall without damaging anything.

Maybe they should apply mild taser shocks to pilots stalling in the simulator. I'm not being snarky. There should be some kind of physical consequence of making bad mistakes, otherwise it's too disconnected from reality.

Re: What really happened aboard Air France 447

#250

Post by lutorm »

jrockway wrote: post #239
lutorm wrote: post #234

Earlier quoted context omitted.

You can be moving backwards relative to the ground and still be overspeed. That's not true. The wind even at altitude won't be more than ~100knots. It's true you can't land using GPS speed, but if your GPS tells you 90 knots ground speed at 37000ft, you know something's not right regardless of wind.

The margin between stall and overspeed is something like 20 knots at that altitude. You're not going to be able to calculate your airspeed from the groundspeed within that margin. (FWIW, I'm pretty sure this GPS speed information is available in the cockpit already. If not, you can get it off your iPhone if you really care.) Finally, the flaps-down speed range of a Cessna 152 is 35-85 kts. So if you're facing into 85…

True about the small margin between stall and overspeed, I didn't mean you could regularly fly like that. But according to the article, their air speed decreased from > 220knots to 90knots. What I meant was that regardless of wind, 90knots air speed should give you a ground speed so low that it should leave no doubt that you are stalled.

Apparently the PF was even thinking they were in overspeed at that point. So a ground speed should have told them that they weren't. But on the other hand, positive pitch angle and -10,000 ft/min vertical speed should also tell you beyond a doubt that you are stalled, so the problem here was not that the pilots didn't have the information they needed to figure out what was going on. They did, but failed to process it. It seems this is a classical case of "getting behind the airplane", they were just not processing events at the speed they were happening.

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