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What really happened aboard Air France 447

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Re: What really happened aboard Air France 447

#231

Post by lutorm »

onli wrote: post #202
StavrosK wrote: post #154

Earlier quoted context omitted.

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...

It's especially frustrating for me because i remember all the times i crashed in a simulator due to stall until i understood what was happening. I don't even remember the name of the simulator, i'm not even an amateur-pilot - but that makes that report almost unbelievable, that something like this happened in a real flight to a real pilot.

unbelievable, that something like this happened in a real flight to a real pilot

Actually, most fatal crashes are "stall-spin accidents", where pilots stall the airplane near the ground without sufficient altitude to recover. But those are not cases where you keep the airplane in a deep stall for 90s. When you stall an airplane in VFR, it's obvious what happens.

No one would persist in keeping the airplane at 20 degrees positive pitch while descending at thousands of feet per minute without realizing the airplane is stalled. But here, without outside references and with obvious confusion about the state of the airplane, it was apparently beyond these guys. (Except the captain, whose comment about "no, don't climb" seems to indicate he was on the right track, but by then it was too late.)

Re: What really happened aboard Air France 447

#232

Post by jrockway »

teyc wrote: post #126
Nick_C wrote: post #120

Earlier quoted context omitted.

> how does a plane know it's stalling if the pitot tubes are frozen Angle of attack sensor. AoA is the actual definition of a stall as it measures the point at which airflow breaks away from the wing, reducing lift. Re your other points on computer warnings, cockpits can get pretty noisy when shit happens with various alarms, buzzers, horns and voices going off. There's actually a tendency to reduce the number of dif…

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 many messages, yes, but nothing that endangered the safety of the flight.

In the AF447 case, the crew was getting the stall warning. They did the exact opposite of what you are supposed to do to recover from the stall. Computers were not the problem. (The same thing happened to that Colgan Air flight a few years ago. The crew reacted to the stall warning by stalling the plane even more. The plane tried to physically force the controls to nose down, which is how you recover from a stall, but the pilots fought it. Bad UI was not the problem. Bad flying was.)

Re: What really happened aboard Air France 447

#233

Post by lutorm »

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.

On the other hand, it's not obvious to me that the simulator would behave correctly in this regime either. Having the simulator work correctly in a deep stall is probably not high on their list of priorities. It's possible that this was even the first time ever that an Airbus had been stalled like that, so maybe no one actually knew how it would behave.

Re: What really happened aboard Air France 447

#234

Post by lutorm »

jrockway wrote: post #227
eftpotrm wrote: post #207

Earlier quoted context omitted.

Yes, but when groundspeed with a slight lag is all that's available is it really that much worse than nothing, which seems to be the failure mode at present? I stress I'm not a pilot and I'm sure you'd want to have a Big Flashing Warning Light telling you that ground speed air speed, but there'd seem to be some benefit over nothing at all.

The ground speed is not useful information. You can be moving backwards relative to the ground and still be overspeed. The only thing that matters to the airframe is the airspeed, and the only way to know the airspeed is to sample the air around the plane.

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.

Re: What really happened aboard Air France 447

#235

Post by jrockway »

freemarketteddy wrote: post #116
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…

>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.

No. There is, not surprisingly, another sensor in the airflow for that.

http://www.lindenhillimports.com/images/photof48.jpg

Re: What really happened aboard Air France 447

#236

Post by barrkel »

freemarketteddy wrote: post #116
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…

>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.

Re: What really happened aboard Air France 447

#237

Post by jrockway »

orenmazor wrote: post #107
brc wrote: post #82

Earlier quoted context omitted.

This is an important point as cars nowadays have more and more electronic overrides - everything from traction control to stability control to anti-lock brakes to lane departure warnings (and recovery) to emergency braking and speed control. Most of the later ones (emergency braking, speed control, lane departure) are only on expensvie cars, but within 10 years will be standard equipment on all cars. If not by legisl…

as a cranky old car owner (old? I'm 27 damn it!), I live in fear of the day that I'll have to give up one of my fun 80s/90s hobby cars and get a self driving toaster :/

Presumably you can easily disable the safety systems after you get the thing home from the dealership.

Re: What really happened aboard Air France 447

#238

Post by adrianwaj »

That Bonin guy was so out of his depth, he should've been thrown out of the cockpit, then again the captain was just too laissez-faire. Bonin should've deferred as soon as captain told him to fly into the storm. Instead he chose to be Manuel from Fawlty Towers.

Re: What really happened aboard Air France 447

#239

Post by jrockway »

lutorm wrote: post #234
jrockway wrote: post #227

Earlier quoted context omitted.

The ground speed is not useful information. You can be moving backwards relative to the ground and still be overspeed. The only thing that matters to the airframe is the airspeed, and the only way to know the airspeed is to sample the air around the plane.

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 85kt winds with the flaps down, you're flying backwards and are overspeed. (This can happen with the flaps up too, of course, but winds of 149 kts are a little hard to believe :)

Re: What really happened aboard Air France 447

#240

Post by jrockway »

lutorm wrote: post #233
jrockway wrote: post #224

Earlier quoted context omitted.

(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.

On the other hand, it's not obvious to me that the simulator would behave correctly in this regime either. Having the simulator work correctly in a deep stall is probably not high on their list of priorities. It's possible that this was even the first time ever that an Airbus had been stalled like that, so maybe no one actually knew how it would behave.

Yes, that's possible. I remember reading an article by the author of X-Plane about how stalls are mostly simulated by trying it in the real aircraft and programming something similar, because the airflow dynamics are too difficult to model in real time. (Incidentally, the Cessna 172 is nearly impossible to stall in X-Plane, but somewhat easier to stall in FlightGear. I wonder who's closer :)
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