Originally Posted by notsosmart
I think that you are smelling exhaust from the APU (Auxiliary Power Unit) which is the little jet angine that could in the tail.
Probably not. The exhaust for the APU is positioned so that it will not normally feed back into the air intakes.
What do do smell is the exhaust from other nearby airplanes just as you would smell the exhaust from nearby trucks or cars when stuck in traffic.
It runs most instruments while the plane is being loaded with people/catering/luggage, etc.
The APU provides electrical power and pneumatic pressure (air). Usually not needed at the gate as then you have ground power and ground air. The APU would be started shortly before push-back so that the ground power and air can be disconnected.
Also the hold doors remain open (big gaping spaces) quite a bt, and probably suck in quite a bit of the exhaust from other planes taking off/taxiing, etc.
No. Air is being pumped in through the air conditioning system. This creates a slightly higher pressure inside the cabin so air is leaking OUT any openings, not IN.