Where does the APU exhaust discharge?

The APU (Auxiliary Power Unit) exhaust discharges at the aft end of the aircraft. This is significant for several reasons. The APU serves to generate electrical power and provide pneumatic air for starting the main engines, as well as environmental control for the cabin when the aircraft is on the ground. By placing the exhaust at the aft end, away from where passenger activities and ground support operations typically occur, it minimizes the exposure to exhaust gases and noise. This strategic location also helps ensure that the APU's exhaust does not interfere with the aerodynamics of the aircraft during flight.

The other locations mentioned, such as the upper side or forward section of the aircraft, would not be practical due to potential safety hazards and operational inefficiencies. For instance, discharging at the upper side could lead to increased risk of ingestion during takeoff or landing if not properly directed, while the forward section could expose ground personnel and passengers to harmful exhaust fumes. The side of the fuselage might also not offer the same level of efficiency in terms of managing airflow and noise suppression as the aft end does.