Multiple Use of Engine Bleed Air in Aircraft

Engine bleed air from aircraft is being used, for decades, for a variety of purposes, whether it is starting the engine, anti-icing and cabin pressurization. Let’s take a look as to how engine bleed air works:

Hot, High Pressure Engine Bleed Air

The air that enters a turbine engine passes through a series of compressors. This increases the temperature and pressure of the air significantly. This hot and pressurized air is mixed with fuel and ignited.

A small portion of this compressed air is redirected from the engine through ducting, valves and manifolds to different areas of the aircraft. The temperature and pressure of this engine bleed air is quite high, ranging from 200 to 250 degrees C and around 40 psi.

Air Conditioning and Cabin Pressurization

The air at high altitudes is not thick enough to fulfill human oxygen requirement. The engine bleed air is utilized to create the required pressure in the cabin along with maintaining the desired temperature. The air that leaves the engine is cooled as it passed through the air-conditioning pack. Before entering the cabin, this bleed air is combined with re-circulated cabin air.


High temperature bleed air helps pilots fight against icing. It passed through the leading edges of empennage and wing, as well as key components of engine for example inlet guide.

Engine Start

Auxiliary power unit is located in the rear of the aircraft. It does not produce any thrust. The high pressure bleed air from this unit serves a pneumatic energy to initiate blade rotation in a main engine.

Water and Hydraulic System Pressurization

Engine bleed air also provides pressurization for the water and hydraulic system reservoirs. This pressurization is used in propelling drinking water to the cabin from the holding tank. In the absence of sufficient atmospheric pressure, smooth flow of hydraulic fluid to the pump inlet is also maintained.

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