What type of air is expelled from the APU exhaust?

The air expelled from the APU (Auxiliary Power Unit) exhaust is classified as hot air. The APU functions primarily to provide electrical power and bleed air for cabin pressurization and engine starting while the aircraft is on the ground. When the APU is operational, it burns fuel to generate the necessary energy, which subsequently produces hot exhaust gases as a result of this combustion process.

This heat is a byproduct of the energy expended in powering the APU's systems and generating bleed air. Therefore, it's essential to recognize that the exhaust is indeed warm, justifying the classification of the expelled air as hot air. Understanding this aspect can help in comprehending the operational characteristics of the APU and the effects it may have on surrounding aircraft systems and structures during operation.