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How long can it take for the APU to start?
Up to 120 seconds
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What are two requirements to start the APU?
Battery switch on
APU inlet door fully open
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What happens if the APU has not started by the end of the start cycle?
Auto shutdown
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What happens if the APU GEN OFF BUS light has not illuminated by the end of the start cycle?
Auto shutdown
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If the APU senses a fault, what happens?
Auto shutdown
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What are some of the things that will cause an auto shutdown of the APU?
Fire
High oil temperature
Low oil pressure
Overspeed
High EGT
Overspeed
ECU faults
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How long should the APU be operated before using it as a bleed source?
One minute
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When the APU switch is moved to OFF, does the APU shutdown immediately?
No
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How could you shut down the APU immediately?
Turn off the battery switch or pull the APU fire handle
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During engine start, does the APU ECU favor bleed air or electrical load?
Bleed air
Electrical load is favored all other times
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How do you know if the APU is ready to accept a bleed air or electrical load?
APU GEN OFF BUS illuminates
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Can you operate the APU with the MAINT light illuminated?
Yes
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Can you operate the APU with the LOW OIL PRESS light on?
No, it will auto shutdown
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Will an APU LOW OIL PRESSURE alert shutdown the APU before the start cycle is complete?
No
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Approximately how long does it take for the APU inlet door to close?
20 seconds
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How many packs will the APU supply on the ground and in flight?
Ground: Both
Flight: One
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How does the APU receive fuel?
A DC fuel boost pump operates automatically when low fuel pressure is sensed. With AC power, the APU feeds from the left side of the fuel manifold. If the AC and DC pumps are not operating, fuel is suction fed from the #1 tank.
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APU shutdown occurs approximately how long after the switch is moved to OFF?
60 seconds
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How does APU automatic load shedding work?
In flight: if the APU is the only source of electrical power, all galley busses are automatically shed. If electrical load still exceeds design limits, both main busses and mission busses, mission AC busses, selected mission 60 Hz AC and selected DC mission busses are also automatically shed. On the ground: the APU attempts to carry a full electrical load. If an overload condition is sensed, the APU sheds galley busses first and then main busses and mission busses until the load is within limits. Manual restoration of galley power can be attempted by moving the GALLEY Power Switch to OFF, then back ON
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What does #5, 6 indicate?
5: Illuminated (amber) – indicates APU detector loop has failed.
Note: MASTER CAUTION and OVHT/DET system annunciator lights illuminate.
6: Illuminated (amber) – indicates APU extinguisher bottle has discharged
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What happens when you pull the APU fire handle?
-arms APU extinguisher circuit
-closes fuel shutoff valve, APU bleed air valve, and APU inlet door
-trips generator control relay and breaker
-allows APU fire switch to rotate
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What do #1, 3, 4, 5 mean?
1: Illuminated (blue) – APU maintenance problem exists: APU may be operated
3: APU RPM limit has been exceeded resulting in an automatic shutdown overspeed shutdown protection feature has failed a self–test during a normal APU shutdown if light is illuminated when APU switch is placed to OFF, light extinguishes after 5 minutes
4: A malfunction exists causing APU to initiate an automatic shutdown if light is illuminated when APU switch is placed to OFF, light extinguishes after 5 minutes
5: During start until the APU oil pressure is normal oil pressure is low causing an automatic shutdown (after start cycle is complete) if light is illuminated when APU switch is placed to OFF, light extinguishes after 5 minutes
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BOLD FACE for APU FIRE
1. APU fire switch Confirm...Pull, rotate to the stop, and hold for 1 second
2. APU SWITCH OFF
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APU fuel burn FL 350 and above
100 LB/HR
(QRH)
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In the event a fire is detected in the APU when the airplane is on the ground, will the fire extinguishing system automatically discharge the APU fire bottle?
On aircraft 203 only, the APU fire extinguishing system will automatically discharge the APU fire bottle 10 seconds after detection (if the airplane is on the ground and the engines are shutdown)
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