To Pool:
If you're out of thrust, retarding is not necessary.
What if they had firewalled with such a switching? - It would have saved their day, wouldn't it?
This is some silly behind the desk comment. If you are in a emergency situation without thrust, you really don't care about technicalities, formalities, bulletins, sops or similar: Anything that gives you a notch more is very welcome....
Although i agree with you this was an emergency situation and lacked thrust, i was only explaining how the system functions, how the 'hard alternate' mode is designed and operated. Obviously it was not designed with the BA038 incident in mind. Fact remains that there is no thrust limit protection and that is why thrust levers are (partially) retarded if fire-walled and that is how operation in this mode is trained. N1, N2, and N3 overspeed protection remain available. Again, with hindsight, in the case of BA038 none of these limits would probably have been reached. And again with the crew not exactly knowing what was affecting the engines might or might not have followed trained alternate mode procedures, all hypothetical anyway because they had no indication or alert to select the alternate mode and most likely never did.
airfoilmod:
Alternate mode selection does not lock out the thrust levers which, in this case, do not have to be fully retarded to idle and as FullWings explains, in this mode N1 becomes the controlling parameter.
Green-dot