AF447 stalled but crew maintained nose-up attitude

[colmbo]

IFR - Instrument Flight Rules, where there is little or no visibilty outside of the cockpit (fog, clouds, rain, etc), you fly and navigate by instruments

VFR - Visual Flight Rules - you can see outside, you fly and navigate primarily by visual reference

IFR and VFR have nothing to do with being able to see...they are definitions of the rules used to conduct the flight.

IMC and VMC (Instrument or Visual Meterological Conditions) relate to visibility and/or ceiling/cloud conditions.

[TonyJoey]

I'm obviously not a pilot either, but I've experienced a similar type of stall in Falcon 4. The plane will repeatedly oscillate up and down at AoA's well above the 25* limit on the F-16, while you fall toward the ground. The only way to get out of them is to override the Flight Control System and rock your way out of it with elevator. I'm not sure how well an airbus would fare with such harsh inputs though?

[icepac]

I can't see them mushing in all the way down without realizing it.

There had to be some sort of overspeed to airframe failure at some point.

More time to reduce the data and testing in same type plane will eventually yield the answer.

[CAP1]

I can't see them mushing in all the way down without realizing it.

There had to be some sort of overspeed to airframe failure at some point.

More time to reduce the data and testing in same type plane will eventually yield the answer.

 disorientation. listening to your senses, rather than trusting your instruments.

[Angus]

I saw a crash the other day, and it was a complete and absolute pilot's mistake. Stall.
However, 3-4 minutes of mushing down at some 100 kts is really funny. You'd have thought that there was plenty of time to nose-down and gather some speed.
Was there downstream? It is nasty, experienced it once as a right-seater with an old hand on the controls of a Cessna 172m, and in what looked like harmless weather, it took full power just to maintain altitude.
But....the airliners like the airbus have a lot bigger envelope. And the aircraft sort of corrects stall, look here:
http://www.youtube.com/watch?v=IKBABNL-DDM&feature=related
Is there a possible explanation in that video?

[CAP1]

i think there was mention of the auto pilot being turned off.

 if the crew got it into a stall, and it was night(i don't remember what time this happened), over the water, there is nothing. nothing at ALL for reference.
 had something happened that allowed the aircraft to get into a stall, and the crew got a little "behind the curve" in correcting....now they're going to go on what they feel, rather than what their instruments tell them.

 all that being said, i've obviously not flown anything that big, and am just speculating.

[Golfer]

My question is, how did they not know they were stalling? Instrument failures or not, surely they must have felt the plane buffeting?

A swept wing transport jet isn't a 172. They don't behave the same way.

Whether they seemed to expect stall/AoA protection in alternate law for their flight controls I don't know. What was going through their heads I don't know. I can say it can be disorienting and confusing when you're in a lull to have your whole world go to hell while you're clipping a rock-your-world thunderstorm like they were. I imagine their responses are going to be studied in further depth to help understand the why's of this accident. It's easy to get fixated and I've seen pilots do it when something abnormal happens. From your weekend warrior in a bonanza to a professional aviator with what you'd consider a lot of experience.  It's not that common and usually it just takes a little kick start to get their scan moving again but it's happened.

Many times actually recognizing what failure has occurred can be more difficult than actually dealing with the failure. Getting a bunch of CAS messages (Crew Alerting System, depending on your acronym, Awareness) at night, in a thunderstorm, during a circadian low and troubleshooting just as the airplane gives up and says "you got it" because it doesn't know what to believe isn't easy especially for the first couple seconds while you're absorbing all the information.  After that you start flying and then fixing.  Should it have been managed?  Sure. Why wasn't it?  I'd like to know. I don't know what else this crew saw, felt or thought to led them down the road they were on but I'd like to. I hope we learn.

[Angus]

I said that. To clear up, - a swept wing airliner on full power has hundreds of knots between stall and top cruising speed or VNE. A Cessna 172 has only 50 knots or so between maximum level speed and the stall.
Hundreds of knots, ponder on that.
The average speed in the descent would be very near a hundred knots, or some 10.000 fpm. It means nothing untill one knows what the actual curve was like during the descent.
And the aircraft landing on the sea in a nose-up position would be how an aircraft would normally be landed on water. But did it fall into the water with the nose-up, or make an emergency landing?
Dunno.

[Golfer]

I said that. To clear up, - a swept wing airliner on full power has hundreds of knots between stall and top cruising speed or VNE.

That's correct for flight down low but not at altitude.  The margin between overspeed and stall can get down to 40 knots in normal cruise and less until they eventually meet.  This is depicted in a flight envelope and where they begin to converge is known as "coffin corner" because the aircraft has such a tight margin between overspeed and stall.

[Tordon22]

Further reports on the subject will be most interesting.

[CAP1]

That's correct for flight down low but not at altitude.  The margin between overspeed and stall can get down to 40 knots in normal cruise and less until they eventually meet.  This is depicted in a flight envelope and where they begin to converge is known as "coffin corner" because the aircraft has such a tight margin between overspeed and stall.

this i never knew.

[rogwar]

http://en.wikipedia.org/wiki/Coffin_corner_(aviation)

[Golfer]

this i never knew.

To expand a little (just a little) the maximum altitudes for a given weight will change based on temperature in relation to standard (ISA +/-) but some airplanes at certain weights just can't go above a certain altitude.  At Brand X airline we had a performance manual in each aircraft's library that would be referenced for our max altitude at a given weight.  The airplanes FMS/FMC can compute your maximum altitude and the airplane will get there but depending on the programming would not provide any buffet margin meaning any burble of air that adds even momentarily a higher wing loading could result in a stall. We'd reference this book which had 1.3G charts meaning those weights and altitudes had a built in margin that was 1.3x stall speed for the given circumstances.  This will keep the high and low speed envelopes wide enough with reasonable safety but you can see how if you're heavy and in cruise that flying into a thunderstorm with it's associated turbulence could potentially lead to a stall condition.  My current airplane doesn't have these charts anywhere but we do have two engine cruise charts for a constant speed and long range cruise which one can only assume have these margins built in.  Seeing what the AoA (Angle of Attack) is and the low speed awareness (LSA) cue projected on the primary flight display (PFD) when we're curising tells me there's a comfortable margin.

I usually don't cruise around unless the airplane will maintain .4 AoA or less but in smooth air for longer range (think holding on an arrival when going fast and burning lots of fuel doesn't help anything) can increase it to .5 or .6 with a comfortable margin.  At .8 the stall warning system (stick shaker in this airplanes case) will begin to shake telling you "hey dummy, get me out of here" while the airplane is still flying until 1.0 AoA as displayed on the indicator when the stall occurs.  The point is yes the margin between stall and overspeed can and does get fairly slim especially when operating near the aircraft's ceiling for that given weight.

These guys losing reliable airspeed, combined with a potential legitimate stalled condition and it happening RFN (right friggin now) can be extremely disorienting especially initially.  They seemed to be talking all the way down and were stable enough for (at least my take was) the captain to take his seat back and have control up until impact with the water.  More information and analysis of the data is required but I'm anxiously awaiting to learn something from this.

[FTJR]

I'm anxiously awaiting to learn something from this.

So am I, thanks for the link, it makes horrifying reading.

[Angus]

You need a very high altitude for that margin. (Coffin corner), and since the aircraft did not go "mach" which would have broken it up in the air, we have to look at a possible stall. But stalling all the way to SL leaves you nowhere near the coffin corner.