Air-start system

A bottom boot device (german air starter unit or air start unit, ASU ) is a ground support equipment for aircraft standing on the floor, supplying pressurized air to start the turbines. The bottom boot device can also be combined with a ground power unit (GPU) and provides additional power.

A jet engine to be accelerated before the fuel supplied into the combustion chambers and the continuous combustion process can be initiated for starting to a speed of about 15 to 20% of the maximum speed. Normally it is used the on-board Auxiliary Power Unit (APU ). If the APU but fails, the airport operator, service company or the airline provides a bottom boot device. Aircraft entirely without APU (such as the Boeing 707) are still in military aviation, but rarely encountered in civilian aviation.

Depending on the performance is the bottom boot device, a compressor with a diesel engine or a gas turbine bleed air extraction (similar to an APU), which is mounted on a trailer, vans or trucks. The compressed air generated by the compressor is out with a hose to a special connection coupling on aircraft outer skin and then passes through pipes on the plane to the starter of the engine.

With the pressure of the soil air boot device and the onboard air conditioning system can be operated. Modern devices provide additional electrical energy, for otherwise a separate ground power unit was required and necessary for modern large-engine large volumes of air.