APU System Flashcards
(14 cards)
How many packs can the APU?
2 on the ground
1 in flight
Fuel Supply
Left side of fuel manifold on A/C power
D/C Pump as a backup if insufficient pressure
Suction feed from No1 Tank if no fuel pumps
Inlet Air
Right Side of fuselage
Cooling Air
Opening above exhaust air
Exhaust air creates a low pressure pocket that pulls air into for cooling the APU and oil cooler
Electrical Starting Requirements
Transfer Bus 1 DC Power or Battery Power
Battery Role
Shutting off batter shuts down APU
Electrical Control Unit loses power and cannot monitor APU
Start Sequence
Opening Air Inlet door
Ram door full open initiates start sequence
APU Reaches proper speed
Ignition and fuel provided
After APU reaches 100% wait 2 minutes before bleed air/electrical power
Indications when ready when started using battery power
none
Can the APU be started with a maintenance light
Yes
Time to start
Up to 120 seconds
Automatic APU Shutdown Conditions
High Oil Temp
Low Oil Pressure
Overspeed
APU Fire
Fuel Control Unit Failure
EGT Exceedance
APU Shutdown
Automatic one minute cooldown to preserve life
If fuel valve doesnt automatically close after 30 seconds, fault light illuminated and needs to be shut down with fire switch
EGT or Speed Exceedance
Electrical load shed if starting
Bleed air shed if not by closing inlet guide vane
Load Shedding
Automatic at 92% till 75% (OBIGGS to low)
100% after 4.5 minutes
120% after 20 seconds
