What really happened aboard Air France 447 • Hacker News Board

Re: What really happened aboard Air France 447

#291

Post by js2 » Thu, Dec 08, 2011, 6:40 PM UTC

Priority logic on the dual-sticks. Each stick has a take-over button. From http://www.smartcockpit.com/data/pdfs/plane/airbus/A330/misc...

  • Normal operation: Captain and First Officer inputs are algebrically summed.
  • Autopilot disconnect pushbutton is used at take-over button.
  • Last pilot who depressed and holds take-over button has priority; other
    pilot’s inputs ignored.
  • Priority annunciation:
    - in front of each pilot on glareshield - ECAM message
    - audio warning.
  • Normal control restored when both buttons are released.
  • Jammed sidestick:
    - priority automatically latched after 30 seconds
    - priority reset by depressing take-over button on previously jammed
      sidestick.

There's also a side-stick priority display on each side showing whether the opposite side is using the take-over button.

Re: What really happened aboard Air France 447

#292

Post by presto8 » Thu, Dec 08, 2011, 6:44 PM UTC

munin wrote: post #285

presto8 wrote: post #281

Earlier quoted context omitted.

Thanks for the great summary. I also read the full BEA report which was very informative. Is there ever a situation in a commercial plane where a stall would be a good thing? My non-pilot brain is trying to figure out why the plane would allow a stall even in alternate law mode. I'm sure the Airbus user interface designers know what they are doing, but wouldn't it be possible to make stall protection always enabled,…

as far as I understand, "stall protection" is a feature of the autopilot knowing its current airspeed. you can drive down the road without hitting things, right? what if you're blind?

The plane did have the air speed information, at least at the time it made the stall warnings. Starting at time 2h10m17s, the pitot tubes started working again, the air speed was available, and the Flight Director came back online [page 89 of BEA report]. That is why the plane was able to make the stall warning in the first place.

I also wonder if, once the FD was back online, could the pilots have just re-engaged the auto pilot and the plane would have fixed itself? This is just such a tragic accident when there was nothing at all wrong with the plane for most of the incident!

Re: What really happened aboard Air France 447

#293

Post by crikli » Thu, Dec 08, 2011, 6:46 PM UTC

eftpotrm wrote: post #207

aperiodic wrote: post #177

Earlier quoted context omitted.

GPS gives you speed relative to the ground, not speed relative to the air, which is what's important for aerodynamics.

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.

> I'm sure you'd want to have a Big Flashing Warning Light telling you that ground speed air speed

That light would never stop flashing. :)

Once you get up a couple of thousand feet, even if the flag is hanging flush against the pole on the ground, you're going to have some type of air movement. The higher you go, the higher the windspeed (in general).

Re: What really happened aboard Air France 447

#294

Post by crikli » Thu, Dec 08, 2011, 6:49 PM UTC

gnaffle wrote: post #260

jrockway wrote: post #240

Earlier quoted context omitted.

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 :)

By easier, do you mean that you have to exert more back pressure to have it stall, or that it quickly gets out of the stall? I think it can vary a bit depending on weight and the exact model you're flying. In some models it's difficult to maintain the stall because the nose will just drop. You should get an introductory flight lesson, then you could ask do have a stall demonstrated and see which flight simulator matc…

Yup, intentional stalls give plenty of warning in a trainer.

It's the stalls caused by uncoordinated flight during a steep bank or snap spins caused by exceeding critical angle of attack, regardless of speed, that will kill you. The first is easy to get into in a trainer like a C172. The second won't happen (safely) unless you're in something with a bit less lift and more power, like a Pitts.

Re: What really happened aboard Air France 447

#295

Post by bjornsteffanson » Thu, Dec 08, 2011, 6:56 PM UTC

Sort of off-topic, but does anyone know anything about the software the Airbus (or any commercial aircraft, really) runs? I'd be really interested to know how abstracted the code is from the hardware.

Re: What really happened aboard Air France 447

#296

Post by crikli » Thu, Dec 08, 2011, 6:59 PM UTC

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

Only in a simulator.

A Cessna 152 is a slow, low-powered trainer. It has a never-exceed speed of 141 knots. So for that aircraft to be going backwards AND be overspeed, you'd have to going into a headwind that exceeded 141 knots.

These windspeeds only occur a) during hurricanes/tornados or b) the high flight levels. You're not going to get a 152 out of the hanger during a hurricane and with a service ceiling around 14,000 feet, you're not getting close to the flight levels, which start at 18,000 feet. I supposed you might see some 100+ knot winds on occasion between 14,000 feet, but again, you're not probably going to be alive to attain the necessary altitude.

Re: What really happened aboard Air France 447

#297

Post by jsmcgd » Thu, Dec 08, 2011, 7:19 PM UTC

gwern wrote: post #288

jsmcgd wrote: post #196

Panic seems to be so debilitating in situations like this as stress severely diminishes to ability to think. Is it worth considering making certain fast acting drugs available to professionals that operate in life-threatening environments that would stop or minimize the stress response? I'm not sure if such a drug exists, one that might reduce stress but not also impair other cognitive functions. But it might well be…

Well, there are things like beta-blockers ( https://en.wikipedia.org/wiki/Beta_blocker ), but the thing about emergencies is that they're fast enough that there's not time to pop some pills, much less wait for them to be digested & metabolized & take effect. The whole OP covers, what, 15 minutes it said? The only way beta-blockers might help is if one took them in advance, and they're not perfect side-effect-wise.

Interesting. Things like cocaine (I'm led to believe) act very quickly. I was even thinking that the placebo effect could be leveraged somehow. Perhaps popping a pill that resides in your top pocket could be a first response whenever a situation starts getting a little hairy.

I honestly think it's worth investigating. Why put up with having your stress response decimate your cognitive abilities, especially when you need them most?

Re: What really happened aboard Air France 447

#298

Post by waqf » Thu, Dec 08, 2011, 7:23 PM UTC

presto8 wrote: post #278

brazzy wrote: post #165

Earlier quoted context omitted.

Bonin would have had to realize that the plane is in alternate mode in the first place in order to react correctly. It probably never crossed his mind since he never trained in it, and conversely if he had trained in it, he may have been more likely to at least check. But to me the bigger problem seems to be that such an important change in the plane's behaviour could happen without anyone noticing. I'd consider the…

Bonin had to have known that the plane was in alternate law. In the flight recorder log, at 2h10m05s, there was an audible "cavalry charge" alarm that indicated to everybody in the cockpit that the autopilot was disconnecting (plus message at the same time on the ECAM). Then, on the ECAM message console 1 second later, the message "F/CTL ALTN LAW (PROT LOST)" was displayed: alternate law, protection lost. At the same…

Of course Bonin knew that the autopilot was off. I don't think that's the same as being in alternate law.

Re: What really happened aboard Air France 447

#299

Post by Caballera » Thu, Dec 08, 2011, 7:29 PM UTC

jarek wrote: post #131

jpiasetz wrote: post #113

Earlier quoted context omitted.

Interesting in that account the person in charge said "my aircraft". May have helped with Air France to eliminate the two people pulling on the stick.

The Popular Mechanics account of AF447 leaves out some quotes and doesn't explain their content very clearly, unfortunately, but it appears they were doing that, more or less. "02:11:37 (Robert) Commandes à gauche! Left seat taking control! [...] At any rate, Bonin soon after takes back the controls." Sometime after 2:12:15: "As the plane approaches 10,000 feet, Robert tries to take back the controls, and pushes forw…

i don't know these people and I'm not a pilot, but is it possible the Bonin wanted to crash the plane? I find it hard to believe that he would continue to pull back on the stick almost the entire time and not 'share' that information, and after Robert took control (by stating 'Give me the controls!'. Just wondering if this is something that would be looked into.

Re: What really happened aboard Air France 447

#300

Post by assemble » Thu, Dec 08, 2011, 7:37 PM UTC

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…

Yeah, I don't know about the a/c in question; however, the Colgan crash was a result of the pilot fighting the stick pusher and winning. The stick pusher is not easy to override.

It seems counter intuitive to nose down when you're falling out of the sky, but it's how you recover.