Air France 447 Said To Have Suffered Deep Stall

I suspect that the pilots did not fully understand the "big picture", but were instead focusing on the various alarms and warnings that were going off. A stall is easy to recover from if one has sufficient altitude. Nose down and add power. Very simple. We'll know more on Friday when the initial report is released.

It is of course much easier to blame the pilot and co-pilots who cannot defend themselves than to consider technical malfunction on Airbus and its suppliers and Air France. As for the factual report to be issued tomorrow by BEA, we can only expect "selected" information but no transcripts or recordings that will bring any new information as for the causes of this terrible accident. Just one month prior to the Paris Air Show what can we expect?

This points out the fragility of flying at the very extremes of the aircraft's capabilities. The envelope that these jets fly in is only +-10 KIA, where 10 knots too slow means the jet stalls and 10 knots too fast means it breaks the sound barrier. Stop and think about that for a minute: 10 knots in an aircraft weighing thousands of pounds is not much of a leeway.

I am only flying a DA40 with a G1000 avionics suite, I have no experience with big iron aircraft. But what I do not understand: If the pitot tube(s) get iced, I still have te GPS indictate groud speed. So the malfunction of a pitot tube should be easily recognisable and the GPS provides backup GS and VS indications.

First, stalling a jet is nothing like stalling your local 172. A large transport aircraft is an aircraft no one should ever stall. This is why they are equipped with stick shakers and pusher, as required by their type certificates, to ensure they are never stalled. An Airbus 330 is also a fly by wire aircraft. A feature of this aircraft is computer controlled control surfaces. The computer code governing the control surfaces is designed to never allow the aircraft to enter a stall or even an unusual attitude. Thus, for the aircraft to stall it necessitates that there must be a technical failure. The pilots failed as well if they allowed the aircraft to stall. However, if the technical failure fooled the aircraft to the extent that it would not accept the pilot inputs, there would be nothing they could do. That scenario is theoretically impossible though. If the computer receives data that is contradictory to flight regime limits, i.e., the aircraft accelerates at a high pitch angle with the power at idle, hence not possible, the computers go to a primitive mode in which the pilot inputs control the surfaces directly. At that point the computers will no longer interfere. Should an aircraft of this type already be in a deep stall by the time the computers give up control or by the time the pilots recognize what is happening, it may well be too late.

A deep stall behaves quite differently than a typical stall we all experience in primary and recurrent training.

A deep stall is normally an unrecoverable stall or may require some rather unorthodox maneuvering for recovery. It happens as has already been explained, when the horizontal stab enters the turbulence from the wing and the elevator can no longer exert enough force to bring the nose down. Typically the wing and tail are both stalled, and the wash or turbulence from the stalled wing prevents the tail from doing much of anything.

The tail normally exerts a negative force which keeps the nose up. IE It pushes down behind the CG. If the horizontal stabilizer (stab) stalls the nose drops. There is a balancing act between lift from the wing and lift from the tail. In a deep stall the nose is *usually* quite high and the horizontal stab exerts no lift, either up or down. In instrument conditions, or at night with no outside reference and with instruments lying to you, your senses (and the computer) are likely to interpret this as an acceleration.

Indications are that the plane impacted, or pancaked into the water. The only typical way this can happen is in a deep stall or high angle of attack. However if the plane has flying speed (under control) it will still have a substantial forward speed even with a high angle of attack.

This phenomena (nose high = acceleration) is how simulators can *simulate* acceleration by raising the nose. Conversely acceleration with no outside reference is interpreted as a pitch change. Like Vertigo, no pilot is immune to this. Add to that your instruments are lying to you and it's all over except for the shouting.

Another point to remember is that the larger the aircraft the more momentum it has. Even many light twins may take many thousands of feet to recover when all is going right.

5/27/11

"Richard Quest, CNN's aviation expert, said: "For whatever reason the aircraft speed sensors failed and the A330 went into a high altitude stall. The pilot's actions were unable to recover the aircraft and some might say, made the bad situation worse."

http://edition.cnn.com/2011/WORLD/americas/05/27/air.france.447.crash/

The initial report was released this morning and although no conclusions have been drawn, it's fairly clear that the pilot error was a fundamental cause, due to improper reaction to the stall warning horn. The pilot pulled the nose up repeatedly and according to the report, maintained the nose up attitude (due to control inputs) for the entire 4 minute duration of the rapid descent.

This sounds like the same pilot error that was made by the Continental Connection pilot landing in Buffalo .... he over powered the stick shaker to pull the nose up when the stall warning sounded, causing an aggravated stall at just 1000 feet.

It's hard to believe that 3 experienced pilots could make such a basic mistake and not correct it over a 4 minute period, yet that's what the report implies.