Originally Posted by
double_barrel
Alternatives? $0.1 accelerometer would have been enough ! So would GPS or simple interpolation. The system 'knows' the attitude and what the engines are doing, it knows the ground speed now and what the airspeed was a few seconds ago. Of course those do not give the actual instantaneous airspeed, but it would not require an especially smart system to detect that the airspeed data was simply missing and to use other sources of data to make an approximation that would have been good enough to keep the aircraft flying until the airspeed data stream returned.
The existing system already detected that the input was bad. The problem is that unless you can determine why the input was bad, it can't be trusted from that point on: it might look as expected, but still be off, just by less.
Your alternative sensors can't replace air speed data: inertial speed or GPS speed is ground speed, which is fine for navigating, but for aviating you need the air speed because it determines how close to the limits the plane is: how close to a stall, how close to being overstressed?
"Do nothing" might have been "keep air speed constant by applying power", which is what it was doing before the autopilot turned itself off. That's pretty much what the pilot did, isn't it? And if you change the system behaviour to "do nothing", you may have changed it for situations where it shouldn't have changed (any programmer knows that fixing a bug often introduces new bugs). What you say is "easy to manage" is in fact hard to manage. It is easy for humans, but hard for computers, which is my point.