APU Flashcards
Describe APU
Self-contained gas turbine
Consists of centrifugal compressor, reverse flow annular combustor and two stage axial flow turbine
Accessory gearbox drives two 225 kVA starter generators
One of the SGs changes to a starter motor for APU start
Does the APU supply bleed air?
No
What altitude limit does the APU have?
The APU can be started and operated up to the maximum operating altitude of the aircraft
Moving APU switch to ON position:
Opens APU fuel spar valve
Activates AC or DC fuel pump
Powers the APU controller
APU FAULT light?
APU fault/fire is detected
APU has shut down due to fault/fire
Momentarily during APU controller self-test
APU status display shows:
Rotation speed in % RPM
EGT
Oil pressure
Oil temperature
Oil quantity in quarts
What does the APU battery power?
APU controller (APUC)
Air inlet door
Right APU starter if required
What APU items does the main battery power?
APU shutoff valve
DC fuel pump
Fire detection system
How high can the APU be started without fuel pumps?
14,000 feet
If starting from a cold airplane using battery power, what does the APU wait for?
It waits until the CCS applications are available.
The CCS fire detection and fuel management applications are necessary to start the APU
Where is the fuel supplied for the APU come from?
Left fuel manifold by any operating AC pump or the DC pump in the left main tank
When does theft aft fuel pump supply pressure for the APU?
Anytime AC power is supplied to the aircraft, regardless of its switch position
How many APU starters are used for APU start?
One, and the starter selection is automatic unless battery power is being used, in which case only the right starter is used
APU RUNNING memo message?
Displayed 2 seconds after APU reaches 95%
APU SHUTDOWN EICAS?
APU failed to start, shut down automatically
Moving the APU selector to OFF from ON removes the message and resets the shutdown system, allowing another start attempt
If you lose three generators inflight, what will happen automatically?
The APU will start automatically regardless of switch position
If generators are brought back, APU can be shutdown by switching ON, then OFF
If cannot get generators back, only way to shut off APU is to pull the fire switch
APU COOLDOWN message?
APU in cool down mode, 2 minutes
APU shutdown sequence
2 minute APU cool down
After cooldown, an APU overspeed is simulated to test the overspeed and fuel shutoff protection
This shuts off fuel and APU shuts down
APU controller closes spar valve
CCS turn off fuel pumps
At 15 RPM, APU controller shuts the inlet door
When is the attended APU mode in effect?
Aircraft in flight
An engine is running or starting
When is the APU in unattended mode?
On the ground when no engine is running nor starting
In attended mode, what will cause the APU to shut down, with no cooldown period (6 items)?
APU Fire / Inlet temperature
Overspeed / Loss of overspeed protection
APU controller failure
Speed droop
APU start failure
Inlet door has failed closed
APU LIMIT EICAS?
High EGT
High oil temperature
Low oil pressure
APU will continue to operate
No cooldown if manually shut down
In unattended mode, ALU will shut down immediately for the following (10 items):
APU fire / Inlet temperature Overspeed / Loss of overspeed protection High EGT/Loss of EGT Low oil pressure High oil temperature APU S/G oil filter approaching bypass Air inlet door failed closed APU controller failure Speed droop APU start failure
