When I'm running the APU, the flight deck is quiet- no sound of flowing air at all even with the packs on. Witht he engines off, this is a fairly major ambiance item, however by no means nessecary :) I'm not expecting to actualy hear the APU as it is some distace behind.Tim

Interestingly, you can hear the APU on level D sims! (At least in the classic).And those sims have certified sound systems so I'm starting to wonder whether you actually do hear the APU up front.(Note, it was the APU sound, not the packs as they were switched off)Regards,Mark

"(Note, it was the APU sound, not the packs as they were switched off)"Are you sure it wasn't Equipment Cooling, Mark? (This is electrically driven). Did the sound appear as the APU was spooling up or when the APU Generator was selected?Cheers.Ian.

Hi Ian,It was a cold & dark cockpit, no external power available. Sound came as the APU spooled up. The sound was very quiet and after the packs were switched on (and I guess equipment cooling after the generator was selected) I couldn't make out the APU sound.Regards,Mark

"Sound came as the APU spooled up. The sound was very quiet and after the packs were switched on (and I guess equipment cooling after the generator was selected) I couldn't make out the APU sound."This is usually the case with most Boeings, Mark. On some aircraft you may only notice it for a portion of it's spool up.... it's easier to hear some frequencies more than others..... after that it seems to fade into the background noise of your average airport. I'd imagine your Level D sim would not simulate this kind of thing?When you start or stop an APU it is comforting to hear it do what you've asked it to do, but, apart from that, it's just an annoyance. Just about every day, on my way to the office, I have to walk past the rear end of a 737.... and find it quite deafening at ground level.If it came to a choice, I'd much prefer to see the big engine spool-up sound improved first (e.g. no looping). ;-) I keep thinking my starter motors have failed.Cheers.Ian.