[az_gila]

True, the HSI (artificial horizon) would have settled the question if it could be trusted. The gyros can go bad, so you can't automatically assume the HSI isn't lying, especially if the VSI is going nuts, as I understand it was. Plus, the FCS was apparently trying to fly the plane out of a stall, and fighting the pilots.

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I don't know the redundancy logic for the AH, but looking at the A-330 cockpit it looks like a separate instrument, even if it is a mini-screen instead of mechanical.

http://www.flickr.com/photos/jpavao/4644756009/

I would have also thought that the Pilots Handbook would give details on which instruments are powered by what for use in emergency situations.

I would also hope that the certification authorities would demand some sort of back-up for the triple redundant computer...:^)

[expatpat]

The pilots would know which gyro instruments were powered by electricity and which ones by vacuum, but there are failure modes other than power problems.

It is my understanding that there is no backup to the triply-redundant FCS on the Airbus, other than a back-up software system, but that requires good air-data to work.

I know Boeing has looked at quad-redundant systems but I'm not sure what aircraft they use them on, if any. It is my understanding that Boeing does have a back-up system outside the FC computers, but I'm not sure of that.