Simple question: What is that thing?

[cl-65link]

On the Saab there is a vent just below the tail nav lights and it is there for the outflow valve for the pressurization. The CRJ's apu exhaust is on the fuselage just below and aft of the #2(right) engine.

 

[skydiverdriver]

On the Brazillia, it's the APU exhaust. On the FK-27, it's actually just a hole. It's there in case the rear pressure bulkhead explodes, to make sure it doesn't take the entire tail with it. So, it's a hole vented to the atmosphere from the unpressurized portion of the tail. Hope this helps.

 

[Tim47SIP]

On the ATR 42/72, it is a hole! That would be a bad thing. Wish it had an APU!!!! No more GPU's!!!!