Glueball,
You might be interested in knowing that neither of your suggestions will work in an FAA certified B777. Single Pack operation reduces takeoff weight even more than having two packs working. You aren’t allowed to use the APU for takeoff.
Chaparral,
The majority of the engine life savings come from the initial thrust reduction, I believe that RR quote a 12% increase in blade life for a .01 EPR reduction (RB211-524D4). This saving isn’t constant and at a certain point you will have achieved your maximum savings regardless of further thrust reductions. Therefore turning the packs off to increase the engine savings isn’t really offering you a lot of benefit.
Obviously you should keep a system where you can increase you takeoff weight with Packs Off when required.
Mutt.
[ 06 November 2001: Message edited by: mutt ]