AIR - DESCRIPTION AND OPERATION

** ON A/C NOT FOR ALL

1. General

A. Bleed and Surge Air
(Ref. AMM D/O 49-51-00-00)
The bleed and surge-air system controls the supply of the APU bleed air to the pneumatic system of the aircraft and prevents a load compressor surge.
The bleed and surge-air system supplies the APU bleed air for:

the main engine start,
the air conditioning.

The APU bleed air system, installed in the APU compartment, is made of stainless steel and is fireproof. If one of the ducts breaks, there is no risk.. Overheat sensor elements are installed on the bleed air duct, between the APU check valve and the APU load control-valve. When the overheat sensor elements detect an overheat condition, the APU load control valve will close.
(Ref. AMM D/O 49-51-00-00)
The bleed and surge-air system controls the supply of the APU bleed air to the pneumatic system of the aircraft and prevents a load compressor surge.
The bleed and surge-air system supplies the APU bleed air for:

the main engine start,
the air conditioning.
the Integrated Controlled APU to Rotate Engine (iCARE).

The APU bleed air system, installed in the APU compartment, is made of stainless steel and is fireproof. If one of the ducts breaks, there is no risk. Overheat sensor elements are installed on the bleed air duct, between the APU check valve and the APU load control-valve. When the overheat sensor elements detect an overheat condition, the APU load control valve will close.

B. Accessory Cooling
(Ref. AMM D/O 49-52-00-00)
The accessory cooling system supplies cooling air to the APU oil cooler and to the APU compartment. The system operates independently of the APU load compressor and the bleed and surge-air system.

** ON A/C NOT FOR ALL

2. System Description

Pneumatic System - Schematic ** ON A/C NOT FOR ALL

A. Bleed and Surge Air
The APU load compressor supplies the APU bleed air. The quantity changes with the different bleed air demands of the pneumatic systems. Variable Inlet Guide Vanes (IGVs) (which are installed at the load compressor inlet) control the quantity of the bleed air.
An APU load control valve and a surge control valve are installed on the outlet orifices of the bleed air T-duct. The APU load control valve stops or permits the bleed air flow from the APU to the pneumatic system of the aircraft. The surge control valve prevents a load compressor surge. The excess air passes through the valve to the exhaust duct.
The Electronic Control Box (ECB) 59KD controls and monitors the APU bleed air supply and the surge air flow. You start and stop the bleed air supply with the APU BLEED pushbutton switch, which is on the AIR overhead panel 30VU in the cockpit.

B. Accessory Cooling
The accessory cooling system operates independently of the APU load compressor and the bleed and surge-air system.
A cooling fan supplies sufficient cooling air to the oil cooler to keep the lubricating oil in the correct temperature range. It also supplies cooling air to the APU compartment to remove the heat which comes from the APU surface.
The cooling fan is of the one-stage axial-flow type and the accessory drive gearbox turns the cooling fan rotor.
The compartment cooling air flows through an outlet into the APU compartment.

[Rev.10 from 2021] 2026.04.01 01:30:45 UTC