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Simple question: What is that thing?

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May 14, 2002
I've noticed on the very end of the tail of several aircraft there seems to be an outlet of some kind. What is that outlet called? What is its function? How come a 777 doesnt have one?
That really depends on what aircraft you're referring to. Typically fuel vents and other vents are located here. Fuel dump outlets may also be located here. APU outlets, and even trailing antennaes are often located at the aft end of the fuselage or tailcone. In some cases in light jets and military equipment, a drogue or drag chute may be located here.
I agree, your probably thinking of the APU. But simply stopping at saying it's an APU probably doesn't help much. Here's a quick explanation.

APU stands for Auxillary Power Unit. It is usually a single-stage turbine engine used to supply the aircraft with electrical and pneumatic power while on the ground, typically when at the gate when engines are not running or on taxi.
I don't know about that, guys...speaking from my wealth of knowledge and experience, I'm going to have to agree with the poopie.
737,47,67,57 --its the APU Exhuast. 777 has the exhaust back there too but faired into the duck fin tailcone(design courtesy of Douglas) The MD twin jets exhaust the APU over top the right pylon.

Sometimes they go poopie there too. usually after ingesting FOD

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