The inlet door directs air into the APU and splits the air into two sections. Some air is directed to the APU compressor and the rest cools the APU compartment.
The inlet door position is controlled by the ECU, depending on various inputs such as weight-on-wheels signal, Mach number, Total Air Temperature (TAT), and Air Data System (ADS). The position of the inlet door is either fully open, intermediate, or fully closed. The inlet door position is displayed on the STATUS synoptic page as either OPEN or CLOSED.
During the start sequence, the 'APU IN START' status message is displayed on the EICAS page.
The 'APU INLET DOOR' Caution message is displayed on the EICAS. What does it mean?
The APU is limited to a maximum of three start attempts within 1 hour, with _____ between each start. The ECU prevents restart until RPM decreases to less than 7%.
Fuel can be supplied to the APU by:
The APU is self-governing, with automatic start sequencing and automatic protective shutdown:
The APU engine and generator have two different dedicated oil pumps for lubrication and cooling.
The APU engine and generator share the same oil for lubrication and cooling. The oil is cooled by an Air/Oil Heat Exchanger (AOHE). The oil is cooled by an Air/Oil Heat Exchanger (AOHE).
The APU controls are on the APU panel, and on the external service panel. In addition, there is an APU shutoff switch in the APU compartment.
There is an APU EMERGENCY STOP switch in the forward firewall enclosure of the APU compartment. When this switch is pressed, it commands the ECU to shut down the APU.
The 'APU OVERSPEED' Warning message is displayed on the EICAS. What does it mean?
APU indications are displayed on the STATUS synoptic page and status / fault messages are displayed on the EICAS page. APU indications are also displayed on the:
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The APU Electronic Control Unit (ECU) controls and monitors:
The aircraft battery bus supplies electrical power to start the APU. The DC power energizes the ignition and the starter motor. The APU requires:
When the batteries are used to start the APU, battery 1 powers the ECU while battery 2 turns the APU starter.
When the APU switch is selected to OFF, the ECU starts a _____ cool down period. After the cool down is completed, the ECU shuts down the APU and closes the inlet door.
The accessory gearbox contains:
During start, the APU Fuel Control Unit (FCU) supplies the correct amount of fuel for start and acceleration to full rated speed. When rated speed is reached, fuel flow is modulated to meet the demands of varying pneumatic and electrical loads while a constant speed is maintained.
The APU Electronic Control Unit (ECU) is continuously self-monitoring. It initiates an internal power-up BITE test when either BATT 1 or BATT 2 switch on the ELECTRICAL panel is set to AUTO. If it fails the BITE test what will you observe?
The 'APU OIL LO QTY' Advisory message is displayed on the EICAS. What does it mean?
The APU Fuel Control Unit (FCU) only controls the quantity of fuel that goes to the fuel nozzles.
The FCU controls the pressure and the quantity of fuel that goes to the fuel nozzles.
When the RPM reaches _____, it is ready for electrical and pneumatic loading.
The APU engine is a:
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