OVERHEAT AND LEAK DETECTION

The system detects overheat conditions near the hot air ducts in the fuselage, pylons and wings. There are double loops in the wings and the fuselage back as far as the APU check valve and single loops for the pylons and APU. 

The following occur for an APU leak: 

• The APU bleed valve closes 

• The APU BLEED FAULT light illuminates 

• The cross-bleed valve closes 

For a wing leak: 

• The bleed valve closes on the related side 

• The associated ENG BLEED FAULT light illuminates 

• If open, the cross-bleed valve closes (except during engine start) 

• If open, the APU bleed valve closes for a left wing overheat (except during engine start) 

For a pylon leak: 

• The related bleed valve closes 

• The associated ENG BLEED FAULT light illuminates.

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