APU Flashcards
How is the APU started?
- Aircraft batteries
- External power source
- Normal aircraft AC power
What is the main function of the Auxiliary Power Unit (APU)?
It is a self-contained unit that supplies the aircraft with:
PNEUMATIC and ELECTRICAL power
What does the APU provide during on-ground operations?
- supplies bleed air for starting the engines
- supplies air-conditioning
- supplies electrical power
What does the APU provide during takeoff?
- Supplies bleed air for air conditioning (for example, when optimum aircraft performance is required)
[APU bleed ON during takeoff]
*computation is packs OFF but PACK 1 and 2 pb still ON
What does the APU provide in-flight?
‐ It backs up the electrical system
- It backs up the air conditioning
- It can be used to start the engines
What is the basic element of an APU engine?
A SINGLE-SHAFT gas turbine that delivers mechanical shaft power for:
- Driving the accessory gearbox (electrical generator, starter, etc.)
- Produces bleed air (engine starting and pneumatic supply)
The basic element of an APU engine is a SINGLE-SHAFT gas turbine the delivers power for:
- Driving the accessory gearbox (electrical generator, starter, etc.)
- Produces bleed air (engine starting and pneumatic supply)
Is a full-authority digital electronic controller that performs the bulk of the APU system logic for all modes of engine operation:
Electronic Control Box (ECB)
What is an ECB?
Electronic Control Box
A full-authority digital electronic controller that performs the bulk of the APU system logic for all modes of engine operation
What does the Electronic Control Box (ECB) provide for the APU system?
Performs the bulk of the APU system logic for all modes of engine operation, such as:
- Sequences the start and monitors it
- Monitors speed and temperature
- Monitors bleed air
- Sequences the shutdown
- Controls the automatic shutdown
This allows external air to reach the compressor inlet of the APU:
APU air inlet flap
Where is the APU air intake flap located?
At the bottom of the tail cone, beneath the APU compartment
What controls the APU starter?
The ECB (Electronic Control Box)
When does the APU starter engage?
- When the APU MASTER switch and START pb is switched ON
and
- When the APU intake flap is FULLY OPEN
When the APU MASTER switch and START pb is switched on, what else is needed in order for the APU starter to engage?
APU air inlet flap fully open
Where is the APU located?
In the unpressurized tail cone
After the APU MASTER sw has been turned ON, the ECB will not allow an APU start until:
The APU air inlet flap is fully open
What are the two (2) things needed in order for the APU starter to engage?
- APU MASTER switch and START pb ON
- APU air inlet flap fully OPEN
When the APU MASTER switch and START pb is switched ON with the APU air inlet flap still fully closed, will the APU starter engage?
NO.
The APU air inlet flap MUST be FULLY OPEN
(Together with the APU MASTER switch and START pb ON)
The APU fuel system is normally supplied from?
The LEFT fuel feed line.
The required pressure is normally available from the tank pumps
What happens if the required pressure from the left fuel feed line is not available (batteries only or pumps off)?
The APU FUEL PUMP starts automatically
When does the APU FUEL PUMP turn ON?
Provided that the APU MASTER sw is ON:
It starts AUTOMATICALLY when the required pressure from the fuel feed line is not available.
The ECB controls the fuel flow.
When does the APU Fuel pump operate?
If no fuel tank pump is running
The APU bleed air system is fully automatic. True or False?
True
The flight crew uses the controls on the APU panel for routine shutdown. What are other controls can be used in case of an emergency shutdown?
- The flight crew can use the APU FIRE pb (cockpit)
- The ground crew can use the APU SHUT OFF pb on the inter-phone panel under the nose fuselage
What happens with an APU fire on-ground?
- The APU fire warning operates
- A horn in the nose gear bay sounds
- The AVAIL light goes out
- The APU MASTER sw FAULT lt comes ON
- The APU shuts down
- The APU fire bottle discharges
During an APU Manual shutdown sequence, if the aircraft was using APU bleed air, the APU keeps running for a cooling period of how long?
60 to 120 seconds
When does the APU Master switch amber light come on?
When an APU automatic shutdown occurs
What happens during an APU automatic shutdown?
Depending of the version of the ECB:
- The amber fault light comes ON
- A caution appears on ECAM
An automatic APU shutdown occurs in case of:
Name three causes
- Fire (On-ground only)
- Air inlet flap closed
- Overspeed
- No acceleration
- Slow start
- EGT overtemperature
- No flame
- Reverse flow
- Low oil pressure
- High oil temperature
- DC power lost (BAT OFF when aircraft on batteries only)
- Overcurrent Sensor failure
- IGV failure
- ECB failure
- No speed
- Underspeed
- Loss of overspeed protection
- Oil system shutdown
- Inlet overheat
- Clogged oil filter
- Loss of EGT thermocouples
What does an amber fault light on the APU Master sw pb indicate?
An APU auto shutdown has occured
During the APU cool down period, can the APU be turned back on?
Yes. As long as it is within the 60 to 120 second cool down period, and the AVAIL light is still on, the APU MASTER sw can be turned back ON.
During an APU start sequence, when does the green AVAIL lt come on (on the START pb)?
When N is above 99.5 % or 2 s after N reaches 95%
After the APU has been started and is on speed (95% N) the green AVAIL light appears in which three locations?
- APU Start pb
- ECAM APU System page on the SD
- E/WD memo section
What happens during an APU fire in flight?
The flight crew must manually shutdown the APU by pressing the APU Fire pb and manually discharge the fire bottle/agent.
What is different about an APU start using the aircraft batteries?
Nothing. Everything is the same except that the APU System page does not appear on the ECAM SD page.
When the APU Bleed Valve is open and supplying bleed air, the APU AVAIL line on the ECAM memo is replaced with what line/message?
APU BLEED
Can the APU be started and operated even if the LOW OIL LEVEL ECAM advisory is displayed?
Yes. If there is no oil leak, then the remaining oil quantity allows normal APU operation for about 10 hours. (Ref: ECAM Advisory conditions)
Maintenance action is required within 10 hours of APU operation.
