The only real info I could find is this matter is this:
> Is there a list of external drives that are verified
> to be able to power down when used with airport
> extreme?
The AEBSn will NOT power down ANY USB disk connected to it. That is the expected behavior.
If a disk goes to sleep by itself, it will not be recognized again by the AEBSn until the station is power cycled or rebooted.