APU Flashcards
What brand APU do we have?
Hamilton Sundstrand APS 2300
What type of engine is the APU?
Single-stage gas turbine engine
What is the purpose of the APU?
To provide pneumatic air pressure and AC power
Which fuel tank is the APU normally supplied from?
Normally fed from the right wing tank
How can the APU receive fuel in abnormal operations?
Fed from the left tank via the crossfeed valve (XFEED LOW 2)
If there is a complete loss of AC power (electrical emergency), how will the APU operate?
The ejector pumps should provide fuel to the APU with the engines running. The DC fuel pump will supply fuel pressure from the right wing if the engines have failed.
If the engines are not running, what will normally provide fuel to the APU?
The AC power will provide fuel via the AC fuel pump
When does the APU’s FADEC shutdown the APU on the ground automatically?
Overspeed/underspeed, high oil temp/low oil pressure, overheat, fire, FADEC critical fault, sensor failure
When does the APU’s FADEC shutdown the APU in flight automatically?
Overspeed/underspeed, FADEC critical fault
How is normal APU start/shutdown controlled?
By the APU selector knob
What happens when the APU selector knob is turned OFF?
Removes pneumatics only, placing the APU into a 1-minute cool down period before shutting it down (to cancel the shutdown, deselect ON within 1 minute)
What is the APU EMER STOP button used for?
An abnormal shutdown without a 1-minute cool down period, closed both bleed air SOV and illuminates white
After the APU is started, when are electric power and pneumatic pressure available?
Electrics and pneumatics will be available via system logic (usually around 95% plus 3 seconds)
Describe the APU
Constant speed, single-stage impeller (impeller pump) with a 2-stage axial-flow turbine, with an independent oil system
What controls the APU?
A dedicated FADEC
What battery is used for the APU start?
BATT 1 powers the FADEC and EICAS for monitoring, BATT 2 powers the starter
What fuel pump is used for APU start?
Batteries ON only DC fuel pump in right tank; AC powered airplane ACMP 2; Right engine running Ejector fuel pump
Will the APU shutdown automatically if speed and acceleration rate isn’t reached in starting cycle time?
Yes. The limitation is 1min ON.
Can the APU shutdown be cancelled?
Yes, by moving the START switch back to ON before the 1-minute cool down is over
What will happen if batteries are turned OFF during the 1-minute cool-down period? (Pilot wants to leave the airplane early)
APU will shut down immediately
Can the APU be started after a critical fault?
No
When will automatic shutdown of the APU occur on the ground and in flight?
Ground - overspeed/underspeed, high oil temp/low oil pressure, overheat, fire, FADEC critical fault, sensor failure; In Flight - overspeed/underspeed, FADEC critical fault
Normal operating range for APU?
100%
What altitude is APU start limited to?
30,000’
What altitude is APU operation limited to?
33,000’ which includes electrical generation
What is the max altitude for APU-assisted engine start?
FL210
What is the max altitude for APU to supply bleed air to the AMS?
15,000’
Where is the air inlet for the APU?
The bottom of the tailcone with a mesh screen to minimize ingestion of FOD
What are the mechanical components of the APU?
FADEC
Compresser impeller
2-stage axial turbine mounted on a rotor shaft
gearbox assembly driven by the engine rotor shaft reduces the engine rotor speed to drive the:
40KVA oil cooled AC generator
oil pump assembly
Describe the APU start sequence
APU ON - powers APU FADEC and opens APU Fuel SOV
APU START - FADEC energizes the starter controller
APU speed 7%, FADEC commands fuel module to open and energize the exciter
50%RPM - ignition exciter and starter are de-energized
95%RPM +3sec - electric and pneumatic becomes available
When are APU electirc and pneumatic power available after APU start?
95%RPM + 3sec
Describe the APU normal shutdown sequence
APU OFF - pneumatic is immediately removed
If APU GEN is not the onlu source of AC power, then the APU GEN will be taken offline as soon as the switch is OFF
If the APU GEN is the only source of AC power, then the APU GEN will remain on the entire shutdown process
1min cooldown - then Fuel Module Closes
spooldown period
(APU SHUTTING DOWN dissapears at the end of spooldown period)
