APU Flashcards
APU start sequence
- ) Battery Master on
- ) Wait 30 seconds then test the fire system
- All 9 fire lights should illuminate and 2 master warning lights illuminate
- FIRE SYS OK advisory message
- ) Anti-ice off
- ) Batteries (main and APU) above 22volts
- ) Press the APU PWR/FUEL switchlight and check for the following messages
- APU DOOR OPEN
- APU IN BITE status message
- APU EGT and RPM gauges are displayed
- APU SOV OPEN status message
- ) Wait for APU IN BITE status message to disappear
- ) Press the APU START/STOP switchlight and check for the following
- Start switch illuminates
- APU START message displayed
- APU start light extinguishes (46-60% RPM)
- APU START message disappears
- APU AVAIL switchlight turns green (99%rpm + 2 seconds)
APU shutdown sequence
- ) Press the START/STOP which deselects it
- ) AVAIL light should extinguish
- ) Wait for for the APU DOOR CLOSE indication to appear
- ) press the PWR/FUEL switchlight which deselects it
- ) APU RPM and EGT gauges should disappear after approximately 10 seconds
How does the GCU command the the APU to stop?
It commands an APU over speed condition which tells the APU ECU to shut down
What is the APU priority?
Electrical first, then pneumatics
What is the APU rating?
40KVA, 115VAC, 400HZ, 3 Phase
What is the APU ECU?
Electronic control unit. It controls and monitors all facets of APU operation.
How is an APU compressor surge prevented?
By venting some compressor air overboard via a surge control valve
What’s the APU’s maximum operating altitude?
41,000’
What’s the maximum altitude for APU starting?
37,000’
Maximum altitude for APU bleed air extraction?
25,000’
Where can you get a textual description of the position of the APU door?
EICAS primary page
What does it mean when the APU door position on the status page is a sequences of dashes?
The APU door position is unknown
Is there a hazard area for the APU exhaust?
No, due to the height of the exhaust.
Does the APU share oil with the engines?
No, it has its own self-contained oil system
How is the APU oil cooled?
It’s cooled via a heat exchanger. APU intake air passes directly over the cooling fins of the heat exchanger. This air is then used to ventilate the APU compartment and then exhausted out the tail pipe.
What happens on the ground when the APU ECU sends high oil temperature or low oil pressure?
ECU automatically shuts down the APU
What happens in flight if the ECU senses a loss of APU oil pressure or high APU oil temperature?
You’ll receive a caution message on the EICAS primary page, but the APU will continue to operate.
Where does the APU get fuel from?
The left collector tank
What provides fuel pressure for APU start and operation?
A dedicated APU fuel pump, which takes fuel from the left collector tank
What valve allows/disallows fuel to flow to the APU?
APU fuel shut off valve (SOV)
If the APU fuel pump fails while the APU is running, what will happen?
An internal bypass valve will open, and the high-pressure, gear-driven fuel pump draws in fuel, allowing the APU to keep running.
Which batteries are required for APU start?
Both APU and main batteries
What is the minimum battery voltage for APU start?
22V minimum on both batteries
Which battery supplies power to crank the APU starter?
APU battery
Which battery supplies power to the APU ECU?
MAIN battery
What will happen during an APU flameout?
The high-energy ignition unit, controlled by the ECU, will energize the igniter and attempt to auto relight.
Maximum APU RPM
106%
Maximum APU EGT
806ºC
Minimum ambient temperature for APU starting
-40ºC
APU starter motor limitations
- A two minute delay must be observed between APU starter cranking attempts to allow for APU starter/contactor cooling, and APU fuel drainage.
- No more than three start attempts in a one hour period
When is the APU surge control valve command open automatically by the APU ECU?
When the APU is supplying electrical loads above 17,000’. This reduces APU surge potential.
What controls the APU load control valve?
Both the ECU and the ACSC. Generally the load control valve is modulated to provide 45psi to the common bleed air manifold.
How can the APU be shutoff externally?
2 ways. Via an emergency stop switch in the APU compartment on the forward firewall. Also via a guarded APU shutoff switch inside the external service panel on the right side of the nose.
Where can you pictorially see the position of the LCV?
ECS synoptic page
Can the APU supply bleed air to the anti-ice system?
No. The system logic prevents this.
What does it mean if “PUMP/FAIL” is indicated on the APU PWR FUEL switchlight?
That the APU fuel pump has failed
What does it mean if “SOV FAILED” is illuminated on the APU PWR FUEL switchlight?
That the APU fuel shutoff valve is in an uncommanded position.
What are the for small exposed tubes on the left side of the aft fuselage near the tail cone?
APU drains
What happens when you press the APU fire switch?
In no particular order…
- ) The ECU closes the APU fuel SOV (if not already automatically done)
- ) The APU fire bottle squib is armed and the BOTTLE ARMED PUSH TO DISCH switchlight is illuminated
- ) APU fuel solenoid valve is closed
- ) APU load control valve (LCV) is closed
- ) APU generator is tripped offline
Will the APU fire extinguisher automatically go off in flight?
No
Will the APU fire extinguisher bottle automatically go off on the ground?
Yes, 5 seconds after the APU fire is detected
