NB I am not an aviation professional.
I saw a documentary about the terrible Air France 447 disaster the other day.
I was struck, as were the experts in it, including David Learmount, who's known as a great aviation expert here in the UK, by the way all 3 pilots were completely unable to grasp what was really happening because of their fatal inability to trust the electronic instruments.
I had a thought: is it not the case when flying any aircraft, whatever its size, that you always need to know, particularly in an emergency, two things?
- air speed
I know this is VERY VERY obvious, but please bear with me.
The fact of the matter is that you can obtain totally reliable information about both these aspects, regardless of darkness, regardless of electronics, regardless of Pitot tubes, at all times:
- air speed: by having an incredibly robust, small structure outside the front of the cabin window which would flex visibly according to windspeed, thereby making the invisible (air flow) slightly less invisible: at 0 knots this would be inclined downwards; at over 150 knots the windspeed would cause this to become fully horizontal. Lack of horizontality would therefore indicate a low speed. One thing I have appreciated since posting this question is the intensely hostile environment this structure would be facing: freezing temperatures, high windspeeds, sometimes containing ice, etc. No doubt one of the reasons why during the development of aviation this has not been considered possible. But materials are being developed now which are much stronger than ever previously known. One candidate might be carbyne. It would also presumably have to be heated.
- attitude: by having one of those completely mechanical floating compasses (as used on ships) in a prominent position in the cabin. Much confusion has been created in some of the comments about apparent gravity. But apparent gravity has effect only when acceleration other than gravity (down!) and lift equal to 1G (up!) is present. The fact of the plane accelerating/decelerating (in any or all of the 3 dimensions) could be indicated by a system of calibrated inertial accelerometers in all 3 dimensions, with lights varying in intensity according to acceleration.
Obviously such a bendy thingy would have to be very tough to withstand the speeds, battering, temperatures, etc. But it is at least conceivable that this is not beyond the wit of humanity. Designed carefully, a change in the way it was flexed would then indicate without any possible doubt when an aircraft was in or near a dangerously low speed.
Wouldn't these two measures have had a good chance of providing the pilots of AF 447 with a true and totally irrefutable mental picture of what was actually going on?
PS it has been objected that such a system, even if feasible, would be redundant. But redundancy in critical systems is a desirable thing: what's worrying is if you don't have redundancy, and the aviation industry has made gaffes in the past over insufficient redundancy: Boeing 737 rudder issues; MD80 horizontal stabiliser: "The absence on the McDonnell Douglas MD-80 of a fail-safe mechanism to prevent the catastrophic effects of total acme nut loss" (Alaska Airlines 261, NTSB report quoted).