APU System

Question 1

During normal operation, from what fuel source does the apu receive fuel?

Answer 1

The left fuel feed line supplies the APU. The required pressure is normally available from tank pumps. If pressure is not available (batteries only or pumps off) the APU FUEL PUMP starts automatically. The ECB controls the fuel flow

Question 2

If the aircraft is operating on external power, can the apu be started with the bat pushbuttons off?

Answer 2

The APU may obtain power for starting from the aircraft’s batteries or normal electrical system, or from ground service.

Question 3

How can the flight crew manually shutdown the apu immediately in an emergency?

Answer 3

APU FIRE s/w

Master S/W p/b……OFF

Question 4

What conditions causes the apu to automatically shutdown?

Answer 4

Depending on version of the ECB, this amber light comes on, and a caution appears on ECAM, when an automatic APU shutdown occurs, which can happen in case of: 
Fire (on ground only) 
Air inlet flap closed 
Overspeed 
No acceleration 
Slow start 
EGT overtemperature 
No flame Reverse flow 
Low oil pressure 
High oil temperature DC power lost (BAT OFF when aircraft on batteries only) 
Overcurrent 
Sensor failure 
IGV failure 
ECB failure
No speed 
Underspeed 
Loss of overspeed protection 
Oil system shutdown 
Inlet overheat 
Clogged oil filter 
Loss of EGT thermocouples

Question 5

hat is indicated when the apu n% speed is displayed in amber or red?

Answer 5

APU N ‐ Displays APU speed in green.

‐ Becomes amber when N ≥ 102 %.
‐ Becomes red when N ≥ 107 %.