Originally Posted by
acl65pilot
Packs off with is for second stage climb performance. Doing it with no APU is because there is a weight penalty for using the APU. (APU door open gives about a 500lb. hit) If the flight was weight critical it probably needed to do it.
Here at DAL, we generally do not leave the APU on, but just take off packs off. We do it on our small engine 767 on every takeoff.
Been a few years since I flew the 757 and the 767, I recall a weight penalty for running the APU on the 767 because of the door design, can someone chime in if there is a penalty for the 757 door. Weeding through some cobwebs, but I don't remember there being a takeoff penalty on the 757 for APU on.
Good question from the O.P. !
FF