Originally Posted by
Waves
May I add my 2 cents? As a former SO LCA on the old 727, we highly discouraged the SO to not run the packs while hooked up to ground power. The obvious reason was that if power dropped, the pack fans would turn off with an instantaneous dual pack overheat and corresponding smoke in the cabin. It's been awhile since I flew the 88 and 90 so I can't remember if it has a similar dilema but it seems like it did. So if you are running the APU and packs on the ground, make sure you are on APU power and not ground power.
Good points - on the 88, I think most people use the APU electrics if its running but I don't remember any specific guidance. On the 90 the power switching is automatic - if the APU is up with the gen on then that's what the airplane is using.