APU Control Panel

Question 1

MAINT light

Blue

Answer 1

• low oil qty for the APU or starter-generator has a shorted rotating diode
• when the oil level is at LOQ, there is enough oil in the APU for 30 - 50 hours of operation at the max oil consumption rate

Question 2

LOW OIL PRESSURE light

Answer 2

• illuminated = oil press low
• auto shutdown occurs in 20 sec
• illuminates during start until oil pressure is normal
• if light is on when APU switch is placed to OFF, it extinguishes after 5 min
• light is disarmed when the APU switch is in OFF position

Question 3

FAULT light

Answer 3

• a malfunction exists which causes the APU to initiate an automatic shutdown
• shows that the APU ECU sensed a fault and a protective shutdown has occurred
• if light is on when APU switch is placed to OFF, it extinguishes after 5 min

Question 4

OVERSPEED light

Answer 4

• illuminates if actual overspeed (106%),
• auto shutdown and light stays on even with switch OFF
• if light is on when APU switch is placed to OFF, it extinguishes after 5 min
• maintenance must reset

Question 5

APU Start switch (3)

Switched to off it:

Answer 5

• starts cool-down cycle
• APU generator breaker trips and the APU bleed air valve closes
• APU continues to run for 60 sec then shuts down