APU Flashcards
The APU should be operated for ________ before being used as a bleed air source
two minutes
The blue GEN OFF BUS Light illuminates when ….
The APU is ready to accept a bleed air or electrical load
T/F: an illuminated LOW OIL PRESSURE light is normal during start until the oil pressure is stabilized.
True
T/F: The APU cannot be operated when the blue MAINT light is illuminated.
False. It can be operated, but maintenance should be notified
T/F: In flight, if the APU is the only source of electrical power, all galley busses and main busses are automatically shed.
True
The APU Bleed Air Valve is ________ controlled and __________ operated.
electrically; pneumatically
T/F: The APU system will automatically discharge the dedicated APU fire bottle when it detects a fire
False. The bottle must be manually discharged.
Immediate manual shutdown of the APU can be accomplished by two methods:
- The APU FIRE switch located on the Fire Protection Panel
- The APU Fire Control Handle located on the Ground Control Panel (aft section of right wheel well)
The APU operates at a _______ speed to meet aircraft electrical demand
constant
Fuel can be supplied to the APU from what 2 sources:
- AC powered fuel pump (left manifold)
- Suction feed from the No. 1 (main tank)
The APU can get electrical power for its start from what sources?
Engine-driven generator, external power
or the battery
T/F: A running APU will shut down if you remove electrical power from it
True. It’s Electronic Control Unit (ECU) requires power
The APU’s Electronic Control Unit (ECU) does what 3 things during the APU automatic start sequence?
- Opens the Fuel Shutoff Valve
- Opens the Air Inlet Door
- Illuminates the LOW OIL PRESSURE light
When the APU switch is moved to the OFF position, the APU will continue to run for a ___________ period at which time its ECU will shut it down.
60 second cooling
What are some of the things that will cause the APU to auto shutdown?
APU Fire, Overspeed, Low oil pressure, High Oil temp, FCU failure, EGT exceedance
The APU amber annunciator lights will remain illuminated for _________ if any of them were illuminated when the APU switch was placed to off.
5 minutes
When will the APU OVERSPEED light illuminate?
- RPM exceedance causing an auto shutdown
- Overspeed shutdown protection feature failed a self test during a Normal shut down
What are the two types of APU airflow?
- Combustion airflow (exhaust)
- Cooling airflow (outside ambient air from the tail section of the aircraft cools the APU compartment, goes into an oil cooler, then exits out with the combustion air)
Bleed air from the APU enters the pneumatic system on which side of the manifold?
Left
Placing the APU switch to the OFF position does what when the APU is running?
- Trips the APU generator of the bus(s) if connected
- Closes the APU Bleed Air Valve
(APU will continue to run during 60 second cooling period)
