APU Electronic Control Box
An Electronic Control Box (ECB) similar to a
Full Authority Digital Engine Control (FADEC) is installed in the aft cargo compartment in the fuselage. The ECB is a single computer that controls and monitors the start and continuous operation of the APU. The ECB is powered by the DC system and backed up by a Permanent Magnet Generator (PMG), which is driven by the APU cooling fan when the APU is running. If the ECB detects an anomaly other than fire,it initiates an immediate protective shutdown with a cooling period. A FAULT light appears on the MASTER SW pushbutton and an ECAM AUTO SHUT DOWN is displayed on the EW/D.An APU protective auto shutdown occurs when:
- Air inlet flap not open
- Overspeed
- No acceleration
- Slow start
- ECB failure
- Loss of overspeed protection
- Overcurrent
- Guiding Vanes failure
- Reverse flow
- Low oil pressure
- High oil temperature
- DC power loss when on batteries only
- EGT overtemperature
- No flame
- Underspeed
- EGT sensors failure
- FCU failure
- Generator high oil temperature
- Ignition failure
- Main start contactor or back start contactor failed open.
An emergency shutdown is commanded by
the ECB when either the APU fire pushbutton on the overhead panel is released out or the APU SHUT OFF pushbutton on the ground crew panel is pressed. If a fire is detected on the ground, the ECB will also initiate an emergency shutdown without any pilot inputs. This feature is only available on the ground.
The ECB will not command an emergency
shutdown if a fire is detected in flight. This
will be discussed further in the Fire Protection chapter. When this occurs, an EMER SHUT DOWN caution message is displayed on the EW/D and the ECB initiates an immediate shutdown without a cooling period even if the bleed air system is used.
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