APU Components

Air Intake & Compressor Section

• The air intake system draws ambient air into the APU. The compressor (often axial or centrifugal stage) increases air pressure before it enters the combustion chamber.

• Essential for supplying both compressed air (for main engine start and environmental control systems) and for running the turbine.

Combustion Chamber & Turbine Section

• Fuel is injected and ignited in the combustion chamber; the resulting high‑temperature, high‑pressure gases drive the turbine.

• The turbine drives the compressor (in many designs) and supplies mechanical power to the gearbox/generator.

Gearbox & Generator / Accessory Drive

• The gearbox takes the mechanical output of the turbine and drives the generator (for electrical power) and other accessory components.

• The generator produces AC (or DC) electrical power that supports aircraft systems (avionics, lighting, air‑conditioning packs) when main engines are off or in backup mode.

Bleed Air / Pneumatic Output

• Many APUs supply bleed air (compressed air) to start main engines and to support environmental control/air conditioning systems.

• Bleed‑air valves, surge control valves and pneumatic ducts are part of this subsystem.

Fuel & Lubrication Systems

• The APU has a fuel system to deliver and meter fuel for combustion.

• Also includes an oil/lubrication system, with oil pumps, filters and coolers to manage turbine and gearbox components.