How does the A320 (or other Airbus FBW aircraft, for that matter) decide which radio altimeter reading to use (say, for FMGC functions like autothrust), or whether to reject the radio altimeter data altogether and throw an ECAM to the pilots? It's certainly not a full voting system, considering that the A320 only has two radio altimeters, not three...
(For the curious: I ask because the flight profile from the ACA 624 mishap bears some resemblance to what would happen if the power rolled back on very short final without the crew noticing.)
