I would not be surprised if the crew thought that since they were using AP B then the AT system would also read from RA on that side and they had no issues due to the captain's side RA malfunction. It's clear that they were very surprised at the low energy state of the aircraft once they found themselves in that situation. I also believe they were complacent to a long engines idle period during descent as it was mentioned in the briefing that they were in a relatively high energy state to begin with, so long engines idle periods were expected.
Of course this does not excuse the lack of airspeed awareness.
For obvious reasons, we will never know what they thought.
Wouldn't it be nice to have an "FDR" for the pilots brain... on the other hand, could be a lot of garbage data there
