Last month, my family flew down to St Thomas, USVI from Atlanta. Down there, they do not use jetways from the aircraft to the terminal. One has to take stairs down from the aircraft into the terminal. They use two stairs, one for the forward door, the other for the aft door.When we were boarding to come back to Atlanta, we had to board the rear stairs. I noticed as we were climbing up the stair, there was a hatch open and felt a slight rush of air going into that hatch. I assumed that was the APU intake. Also it was noisy as heck back there, so my assumption about the APU should be correct. :)My question is this: When the flight crew starts up the APU, do they have to first OPEN the intake and discharge hatches for the APU? Or just by starting the APU itself, those hatches open automatically?I am just curious about that.ThanksJohn BradleyAuburn, Ga

Automatic....

The hatch you were looking at was probably the outflow valve for the cabin pressurisation system as this is situated on the aft left fuselage behind and below the L4 door. The APU intake is on the upper surface of the rear fuselage righhand side situated between the Fin and the Stab and as such it is not very apparent when looking at the aircraft from ground level. The opening and closing of the intake is controlled by the APU ECB (controller).