APU Flashcards
The APU compartment is made of
Titanium
What prevents compressor surge?
The surge control valve
Closed below 17,000 feet
What controls the different of stages of the APU
The electronic control unit
ECU
What powers the ECU?
The PWR/FUEL switch lights on the APU Control Panel
Is the APU door position shown continuously?
YES
When are the RPM and EGT gauges shown on the EICAS status page
Upon selection of the APU PWR/FUEL switchlight
APU Max operating altitude
41,000
Max altitude for starting APU
37,000
Max altitude for bleed air
25,000
Ground starting altitude limit
15,000
What type of engine is the APU
Single shaft constant speed design
two stage turbine
Fuel for the APU comes from
The left collector tank
The APU gearbox has an internal oil sump
.
Where is the inlet door located
Upper right side of the rear fuselage
Controlled by the ECU
How many air inlets door positions on the ground
Two positions on the ground
Closed or open
In-flight it is variable
What does the air inlet door ram air provide air for
APU operation
And
Oil cooling
What happens when the power fuel switch light is pressed
APU IN BITE STATUS MSG
APU SOV STATUS MSG
RPM/EGT gauges
Door opens
APU fuel pump turns on
What happens when the start stop switch light is pressed
Starter is energized(
APU START MSG)
Ignition
Fuel introduced
Start legend on the APU panel comes on
The APU starter is deactivated at
46% on the ground
60% Inflight
What notifies the crew that the APU is ready for loading
Two seconds after the APU reaches 99%
available legend in the start stop switch light illuminates
When the start stop switch light is selected to stop the APU
The APU will automatically shed it’s loading and shut down
When the power fuel switch light is deselected
The fuel shut off valve closes
Power is removed from the ECU
On the ground the APU can be shut down bye
An emergency stop button located in the APU compartment
On APUshut off switch on the external services panel
APU overspeed?
APU shuts down automatically
Ground and flight
20-15 ch 20 Airborne auxiliary power
APU overtemp?
APU automatically shuts down on the ground
APU fault caution?
APU shuts down automatically on the ground
Test
APU high oil temperature
AP will shut down on the ground only
Apu inlet door located?
Upper rt side if fuselage
Minimum ambient temperature for starting?
-40c
How many starts in one hour?
Three starts or start attempts in any hour
What is the primary purpose of the APU?
Electrical power
The APU door is controlled by the?
ECU
Where is the exhaust air mixture vented??
Through the centered tail pipe
What is the APU and main battery voltage required before we start the APU?
22V
How does the APU start sequence differ in the air from on the ground?
In-flight…The APU door will not open until the start stop button is selected
Three ways an APU compressor stall or surge is prevented?
One way check valve in pneumatic ducting
Surge control valve
Control logic of the ACSCs
(Interlock protection)
When will the APU LCV close?
Either PRSOV open
Wing or cowl engine anti-ice selected on..if APU is the bleed source
When selected to manual modeusing an engine as a bleed source
Fuel is supplied to a FCU (fuel control unit) from???
Left collector tank
Via deficated APU fuel pump
What monitors flow of fuel to apu?
FCU
Fuel control unit
( in response to commands from ECU)
Appch bit ldg
Ldg gear dwn
Or
Flaps greater then 20
Appch bit takeoff
TL out of toga
And
Ldg gear up
And
Flaps 20 or less
APU door position in-flight depends on…
Mach number
WOW
Altitude
Apu door positionis dependent on?
Wow
Mach
Apu rpm
Apu door will automatically close when?
During shutdown
And FIRE
B4 starting apu .. bat voltage?
22v
Both main and apu
When does the AVAIL light turn on
99% RPM +2 seconds
What prevents compressor style or surge
One way check valve
Surge
control valve
Control logic of the ACSCs
When start stop switch light is pressed( during shutdown) what happens?
An over speed situation is simulated in the APU shut down
APU GEN OFF CAUTION?
Apu ready for loading and gen switch off ( after 30 seconds)
Apu can never
be used for icing
Bleed misconfig
Apu door in flight vs on ground?
In flight .. apu door will not open until ..
Start/stop is selected
APU Altitude starting a limit
37000
When does the green avail switch light illuminate green?
99% RPM plus2/ seconds
What three things prevent APU compressor stall
One way check valve
Surge control valve
Control logic of the ACSCs
46%
60%
95%
99% + two seconds
Started deactivated on the ground
Starter deactivated in-flight
Ignition turned off
Ready for loading
APU Shuts down on the ground
OVERTEMP
LO OIL PRESSURE
HI OIL TEMP*
ECU Is off of what bus?
BATT BUS
APU start Inflight?
Can restart, rpm blo 12%
APU flameout?
Auto relight function of the ECU
The APU is started from which battery?
The APU battery
