thanks for the links to the report!
I know the whole redundancy issue has been discussed before - but just in general, shouldn't on a airplane every vital function be back-uped? I mean why is the A/T not in general configured to use both radio-alts no matter what?
just out of curiosity, how does airbus handle the subject? do their A/T also only use one radio alt to measure the distance to the ground? (I really don't wanna start some boing vs. airbus discussion!!! just wondering if this A/T configuration is standard (and if so, why?) or not...)
If I'm correct here, the autothrottle is simply linked to the autoland system. It can obviously be used without autoland being activated for cruise and all other phases of flight. The crew of this particular flight was performing a single channel autoland, witch defaults to the left, or #1, Rad Alt. If a dual channel autoland was being executed, the autopilot would have sensed a discrepancy between the two Rad Alts, and disconnected the autopilot. At witch point, the crew would have had to shoot the ILS "old school", using the autopilot with APPR and IAS Speed Hold mode engaged until they obtained visual contact with the runway environment.
So to answer your Q, it can be connected to both Rad Alts, if the right mode is selected.
As far as differences between Airbus, Boeing, Douglas, Tupolov, or any other manufactureer, I am not totally sure on that...