Use of APU's

Most jet aircraft have an APU (auxiliary power unit), a small jet engine which produces power for the aircraft when it is on the ground and the main engines are turned off.

The APU is most often located in the tail of the aircraft. Like other jet engines, it emits some noise when in use. To reduce noise, the APU may only be used for five minutes before the aircraft leaves the stand and five minutes after it arrives at the stand.       
Instead, the aircraft must use the power and ventilation facilities found at most stands. At stands that do not have these facilities, the aircraft can use a GPU (ground power unit), which is a diesel or electric powered generator which emits considerably less noise than an APU.

Each year, CPH performs many inspections to check the use of APUs by aircraft at the different types of stands.

Emissions from an APU engine
Emissions from an APU engine

A GPU in use
A GPU in use at one of the airport's remote stands, which have no fixed power or ventilation facilities.

Power and ventilation connected to an aircraft at a stand