The distribution system uses pressurized air which comes from the engines, the auxiliary power unit (APU), or a ground source.

The distribution system supplies pressurized air to the air-conditioning system, the engine start system, the wing anti-ice system, and the cowl ant-ice system. These systems control the pressurized air through ducts, shut off valves, check valves, and other valves.

Bleed-air from the engine is supplied through a bleed-pressure regulating and shut-off valve, which is found in each engine nacelle.

Bleed-air from the auxiliary power unit (APU) is supplied during ground operation or for a cross-bleed start of an engine in flight. The APU is found in the aft equipment compartment.

The ground connection is installed behind the ground-air servicing-connection door in the lower aft fuselage.

An electrically controlled cross-bleed valve connects or isolates the left and the right air supply systems.

The primary functions of the bleed-air system are what follows:

• Transfer the bleed-air between the low pressure and the high pressure ports
• Control the pressure of the bleed-air
• Control the temperature of the bleed-air supplied to the air conditioning system
• Supply the bleed-air for engine start

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The bleed-air leak-detection system monitors the hot air leaks from the air ducts of the bleed air system, the anti-icing system and trim air valves. This system protects the components and the structure near the ducts against an overheat condition and the risks of fire.