APU Flashcards
What controls & monitors the APU?
A dedicated FADEC
APU Protection: When will the FADEC automatically shutdown the APU in flight?
Overspeed
Underspeed
FADEC Critical Fault
APU Protection: When will the FADEC automatically shutdown the APU on the ground?
Overspeed
Underspeed
FADEC Critical Fault
APU Fire
APU EGT Over Temperature
APU Low Oil Pressure
APU High Oil Temperature
Sensor Fail
How would you carry out a normal APU Shutdown?
APU Master Selector knob from ON > OFF
What happens if you move the Master Selector Knob from OFF > ON during the shutdown sequence?
Cancels the Shutdown
How would you shutdown the APU in an Emergency?
Push the APU EMER STOP Button
What happens when the APU EMER STOP Button is pushed?
APU Fuel Shutoff Valve Closes
APU Shuts down with NO cooldown period
WHITE Striped Bar illuminates on the lower half of the APU EMER STOP Button
When would the upper half of the APU EMER STOP Button illuminate RED?
When an APU Fire is detected
How long is it recommended to wait after the EICAS is energised to attempt a start of the APU?
30 seconds
Which Fuel Tank provides fuel to the APU?
Right Wing Tank
Is it possible to provide fuel to the APU from the Left Wing Tank?
Yes, via the Crossfeed Valve
When only DC Power is available, which pump provides Fuel to the APU?
DC Fuel Pump
(located in the Right Wing Tank)
If AC Power is available (GPU) but the engine is not running, which pump provides Fuel to the APU?
AC Fuel Pump
(located in the Right Wing Tank)
If the engines are running, which pump provides Fuel to the APU?
The RIGHT Ejector Pump
What are the steps to start the APU?
APU Master Selector Knob from OFF > ON
APU Master Selector Knob from ON > START (Momentary Action)
During APU Start, what happens when you move the APU Master Selector Knob from OFF > ON?
Powers up the FADEC
APU Fuel Shutoff Valve Opens
EICAS Indications change from OFF to APU EGT & Rotor Speed
What is the Max APU Continuous EGT?
717°C
What is the Max APU Start EGT?
1032°C
What is the Max APU Rotor Speed?
108%
What is the Max Altitude at which you can start the APU?
30,000ft
What is the Minimum Temperature at which you can start the APU?
-54°C
What is the Max Operating Altitude of the APU?
33,000ft
What is the Max Altitude for APU Electrical Generation?
33,000ft
What is the Max Altitude for APU Bleed Air to assist Engine Start?
21,000ft
What is the Max Altitude for APU Bleed Air for Air Conditioning & Pressurisation?
15,000ft
What are the APU Cooling Periods after each Start Attempt?
1st & 2nd Attempt - 60 Seconds
3rd Attempt - 5 minutes
What is the APU primarily used for?
As an on ground pneumatic source for both the air conditioning packs and engine starting
What is the purpose of the APU?
To Provide:
Pneumatic power - for both engine start, and to supply bleed air to the air conditioning packs
Electrical Power - via an AC Generator
What is the APU, and where is it located?
A Gas Turbine Engine, located in the Tailcone
At what speed does the APU operate?
Constant
Where is the APU Air Inlet Valve Located?
On the bottom of the tailcone
What electrical power does the APU supply?
AC Power 115V 40kVA
When can the APU provide bleed air?
Both on the Ground and in Flight
During APU Start, what happens when you momentarily move the APU Master Selector Knob from ON > START?
The APU Start Cycle is initiated
FADEC commands the electronic starter controller to energise the brushless starter generator, initiating APU rotation
7% - FADEC commands the module to open and energise the exciter
50% - The ignition and starter are de-energised and the APU begins to run on its own
At what Rotor Speed will the APU begin to run on its own?
50%
When will Pneumatic & Electrical Services become available after APU start?
3 seconds after APU has reached 95% Rotor Speed
What happens if the APU does not reach proper speed or acceleration rate within the Starting Cycle time?
The APU will automatically shut down
What does an APU FAIL EICAS message indicate?
APU Automatic Shutdown has occured
Can the APU be restarted following an Automatic Shutdown?
No, unless it occurred during the starting cycle (subject to restrictions)
Following a Normal APU Shutdown when is Pneumatic Power removed?
Immediately
Following a Normal APU Shutdown, when is Electrical Power removed?
Following a 1 minute Cooldown period
(2 minutes PRE MOD)
What happens during a normal APU Shutdown?
APU SHUTTING DOWN EICAS Message
APU Pneumatic Power Removed Immediately
Electrical Power Removed after a Cooldown Period
Spooldown Period (POST MOD ONLY)
APU SHUTTING DOWN EICAS Message Removed
Why does the APU continue to run when selected OFF?
If the APU is the only source of AC Power it remains on for the entire shutdown process including cooldown/spooldown periods.
If it is not the only AC Power Source it will be taken offline as soon as the APU Master Selector Knob is moved from ON > OFF
How long should you wait after APU Shutdown before turning off the batteries and why?
8 seconds, because if power is removed from the APU Fuel Shutoff Valve during its opening/closing, it may result in a fuel leak
