APU EXAM QUESTIONS AND ANSWERS
How many volts are required to start the APU? - Answers - 22
What are the APU start cycle limits using ground power? - Answers - 15 seconds On - 2
minutes OFF,
15 seconds On - 20 minutes OFF,
15 seconds On - 2 minutes OFF,
15 seconds On - 40 minutes OFF.
When does the white APU starter message go out? - Answers - At 50 % rpm.
At what speed will the APU AVAIL light illuminate? - Answers - At 99 % rpm (after 4
seconds)
What conditions will cause the APU to automatically shut down in flight? - Answers -
Fire, Overspeed, RPM signal loss, DC power loss, ECU loss, or a slow start (less than
50% for 60 seconds).
What conditions will cause the APU to automatically shut down on the ground? -
Answers - Fire, Overspeed, RPM signal loss, Loss of DC power, ECU loss, Slow start,
Over temp, Over current, Low oil pressure, High oil temp, EGT signal loss, or loss of
door signal.
What four things happen when you press the APU power fuel switch? - Answers - The
APU SOV opens, the APU intake door opens, APU gauges appear on the MFD, and the
APU in Bite status message appears. (DIGS: Door, In-bite, Gauges, SOV)
The APU ECU protects the APU compressor against surge by opening and closing
what? - Answers - The APU variable diffusers.
Which busses are required for the APU to start? - Answers - The APU battery direct bus
(APU door, and starter). The Main battery direct bus (ECU interface) and the battery bus
(PSEUs and APU ECU).
The APU modulates APU bleed air through what valve? - Answers - The APU Load
Control Valve (LCV)
The APU ECU ensures priority is given to what APU function? - Answers - Electrical
loads.
What will happen if you have an APU fire on the ground? - Answers - The APU will shut
down, the APU Fire-x bottle discharges after 5- second spool down, and an external
horn will sound.
How many volts are required to start the APU? - Answers - 22
What are the APU start cycle limits using ground power? - Answers - 15 seconds On - 2
minutes OFF,
15 seconds On - 20 minutes OFF,
15 seconds On - 2 minutes OFF,
15 seconds On - 40 minutes OFF.
When does the white APU starter message go out? - Answers - At 50 % rpm.
At what speed will the APU AVAIL light illuminate? - Answers - At 99 % rpm (after 4
seconds)
What conditions will cause the APU to automatically shut down in flight? - Answers -
Fire, Overspeed, RPM signal loss, DC power loss, ECU loss, or a slow start (less than
50% for 60 seconds).
What conditions will cause the APU to automatically shut down on the ground? -
Answers - Fire, Overspeed, RPM signal loss, Loss of DC power, ECU loss, Slow start,
Over temp, Over current, Low oil pressure, High oil temp, EGT signal loss, or loss of
door signal.
What four things happen when you press the APU power fuel switch? - Answers - The
APU SOV opens, the APU intake door opens, APU gauges appear on the MFD, and the
APU in Bite status message appears. (DIGS: Door, In-bite, Gauges, SOV)
The APU ECU protects the APU compressor against surge by opening and closing
what? - Answers - The APU variable diffusers.
Which busses are required for the APU to start? - Answers - The APU battery direct bus
(APU door, and starter). The Main battery direct bus (ECU interface) and the battery bus
(PSEUs and APU ECU).
The APU modulates APU bleed air through what valve? - Answers - The APU Load
Control Valve (LCV)
The APU ECU ensures priority is given to what APU function? - Answers - Electrical
loads.
What will happen if you have an APU fire on the ground? - Answers - The APU will shut
down, the APU Fire-x bottle discharges after 5- second spool down, and an external
horn will sound.
