Air France 447 and the Colgan Air crash at Buffalo have injected new vigour into a debate that has been going on quietly in the industry for some years now.
It's about how to teach airline pilots to handle the aircraft when it's close to the edge of the flight envelope.
The debate about airline training for upset recovery (recovery from unusual attitudes) is a part of this, but it's stall recovery specifically that I want to concentrate on here.
For brevity, I am going to assume that readers know that stall is ultimately about angle of attack and that they understand the aerodynamics of a stall, so I can concentrate on existing perceptions about recovery technique, because technique is what the industry debate is about.
Some of stall recovery's finer points are in dispute. Let me set out what I think the case is, and then please feel free to tear my perceptions to shreds; the objective is to discover the truth, if there is a single truth.
During basic training, most pilots are taught to recover from a stall by dealing with the attitude first, accepting some height loss as inevitable, then applying power.
However line pilots, who spend most of their time in controlled airspace, have been taught for decades that they should apply power first, then adjust attitude if necessary to minimise height loss.
I suspect that this technique, blessed by the FAA, was was taught because it was assumed pilots would be reacting to a stall warning, rather than waiting for the actual stall. And the controlled airspace factor means that any loss of altitude would mean loss of cleared vertical separation.
Buffalo has caused a lot of heart-searching at the FAA and National Transportation Safety Board, leading to a re-discovery that the "power-then-attitude" stall recovery technique was not the one that the manufacturers' test pilots were required to demonstrate to win certification for the aeroplane type in the first place: test pilots use the classic "attitude-then-power" recovery, accepting height loss as inevitable. So the FAA, seemingly without noticing, had authorised a line training technique different than the one they required for type certification.
Of course if the "power-then-attitude" technique is applied skilfully, with a due appreciation of basics like phase of flight, density altitude and height, it works. But if applied when the aircraft is thoroughly stalled it will delay stall recovery and risks making the situation worse.
When and why the "power-then-attitude" technique change was accepted is not completely clear, but I have a personal theory. Please feel free to shoot it down:
In the 1950s when transport aeroplanes were powered by big piston engines and props, the power response was instant and gave you lift-producing propwash over the wings, which could assist stall recovery and restore airspeed. Also the thrust line and drag line were almost the same, so there was no pitch-up with power application as there is with today's underwing jet engines. And wings were not supercritical, so the stall was less dramatic.
My theory is that the FAA approved the power-then-attitude system for propliners and then forgot to review it for jets.
I have put this to many worthy senior airline pilots, but have not been able to confirm it. Maybe it's lost in the mists of time.
Finally, has the "power-then-attitude" technique got anything to do with the apparent fact, as demonstrated over the Atlantic and at Buffalo, that pilots both sides of the Atlantic - in big jets and turboprops (Colgan was a Q400) - are at risk of reacting wrongly to stalling?
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