Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

What really happened aboard Air France 447

popularmechanics.com

Post reply on HN
Print view View original

281–290 of 374 posts

Re: What really happened aboard Air France 447

#281

Post by presto8 »

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…

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, and then add a failsafe requiring both pilots to press a button to override stall protection? Then they would both have to consciously do a physical act to enter this dangerous state.

Re: What really happened aboard Air France 447

#282

Post by jrockway »

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…

I've been meaning to start taking lessons so I can get a private pilot's license, but it's hard when you live in downtown Chicago without a car. There are a couple schools at MDW, but you'll eventually have to drive to the suburbs as MDW does not let students fly solo out of the airport. Probably for good reason :)

Re: What really happened aboard Air France 447

#283

Post by arjunnarayan »

Florin_Andrei wrote: post #262
einhverfr wrote: post #166

Earlier quoted context omitted.

BTW, who is commanding the plane (by inputs) and who is commanding the crew are entirely separate questions. I think one of the serious issues that MUST be addressed here is the issue of conflicting commands to the plane. Two options.... 1) Place all controls between the pilots so they can easily see what eachother is doing or 2) Place a selection switch and indicator that allows a pilot to unambiguously take control…

What happens if they're fighting each other?

Then they have to fight! You can't delegate responsibility to the "system" to resolve such a fight. A fight is a fight. And if it's happening, you can't automagically get rid of the fight.

Re: What really happened aboard Air France 447

#284

Post by kristaps »

brazzy wrote: post #165
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…

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…

A mode switch as important as this should be very visible. An idea: put a two-color led under every indicator light and switch to the other color when the plane falls into alternate law. This should make it sufficiently clear that something very notable has just happened.

Re: What really happened aboard Air France 447

#285

Post by munin »

presto8 wrote: post #281
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…

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?

Re: What really happened aboard Air France 447

#286

Post by sowbug »

citricsquid wrote: post #6

The lack of reaction to "Stall!" implies one of two things; either it was broken and the sound didn't play or the complete lack of understanding about what the word "Stall" meant with the pilots. Has either of these been proposed and discussed? The author of this piece doesn't seem to touch on why they ignore "Stall!", unless it's been confirmed the sound had been heard (on the recording maybe?) and they did indeed u…

The Invisible Gorilla by Christopher Chabris and Daniel Simons tries to answer this question. These guys made the video where people are supposed to count the number of basketball passes (I won't say what's actually in the video in case you haven't already seen it).

The pilots were likely afflicted by a form of inattentional blindness. Their brains certainly heard the stall warnings, but they were filtering them out so that they could focus on "the important stuff." People do stuff like this all the time, like crash their cars into motorcycles because they were so preoccupied looking for oncoming automobiles (not bikes).

Re: What really happened aboard Air France 447

#287

Post by lake_rogue »

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…

149 kts occurs daily -- at altitude.

For example the current winds aloft forecast for BML shows 155 kts at 30,000 feet:

http://aviationweather.gov/products/nws/fdwinds/dynamic/bost...

While 149 kts at the 2,000 ft to 12,000 ft typical of Cessna 172 flight is rare, we had it in Seattle last week (wind speeds on the ground were 20 - 3 kts, at 3,000 feet we had 60 kt winds at 12,000 feet we had 100+ kts, can't remember exactly).

I'd guesstimate in the Seattle area it occurs once every 2 months below 20,000 feet. Above 20,000 feet, it's a regular occurrence.

Flying into 85kt winds will not put you overspeed, flaps down or up (assuming you're airborne, and not on the ground). Wind speed has no effect on aircraft air speed.

If you're flaps-up, engine at 2300 RPM, flying straight-and-level you're going to be cruising around 120kts airspeed in a C172 regardless of a 100kt headwind or 100kt tailwind.

Groundspeed is another story all together (and your fuel consumption getting to your destination).

Re: What really happened aboard Air France 447

#288

Post by gwern »

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.

Re: What really happened aboard Air France 447

#289

Post by crikli »

Florin_Andrei wrote: post #245
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?

> What problems specifically?

All aircraft have a VNE speed, the NE standing for "never exceed." Going beyond this threshold invites structural failure and loss of control.

> If you're inside the plane, how does it feel when the plane has stalled?

I've mentioned this in another comment, but the body is a horrible judge of spatial reference. How the body is going to feel during a stall is tough to predict, particularly given that as a passenger a) you will have no visual reference and b) you will be at a unique distance from the aircraft's center of gravity.

That said, you might feel a little buffeting as the wing reaches a critical angle of attack, but once the plane is in a full stall you probably wouldn't feel a whole lot. It's impossible to overstate just how much the body relies on the Mark One Eyeball to properly interpret the sensation motion, gravity, centrifugal force, etc.

Re: What really happened aboard Air France 447

#290

Post by [deleted] »

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.

[deleted]
Post reply on HN