We were taxiing for takeoff at DTW last night, and as I sat in 1D sipping my drink, I couldn't help but notice all the DC-9's pointing their rear ends at me. Sort of like cats looking for affection.

Anyhow, the DC-9 fuselage ends in a sort of wedge-shaped affair. The Airbus (and Boeing a/c, too, IIRC) has a hole there, with a flange around it. Sort of like a jet exhaust, though I know it isn't. Even the little CRJ's seemed to have tiny holes pointing out the back.

What are those openings for? Is it some sort of ventilation device? I did notice that the DC-9's had a set of louvers around the tail; maybe that performs the same function. Whatever that function is.

Can someone enlighten me?