APU Flashcards
What is provided by the APU?
- Provide bleed for engine start
- Provide AC electrical source
- Air for air conditioning Packs
What are main components of the APU?
- Engine
- ECU
- Inlet Door
- Assembly gear box
- Lubrication system
Which part of the APU provides bleed air?
APU engine compressor. The vanes are used to regulate airflow depending on the demand
Where is APU ECU located?
In mid equipment bay
How is APU start supplied
Primarily by DC ESS BUS 2 (from battery)
Secondarily DC EMER BUS
APU needs DC Power to start
What is APU BITE test?
The ECU is continuously self-monitoring. It initiates an internal power-up
BITE test when either BATT 1 or BATT 2 switch on the ELECTRICAL
panel is set to AUTO. If it fails the BITE test, the FAIL light on the APU
panel comes on and the APU FAULT advisory message is displayed on
the EICAS page
Where are APU OFF switches located
What are possible positions of APU door?
The
position of the inlet door is either fully open, intermediate, or fully closed.
What is the function of APU door?
The inlet door directs air into the APU and splits the air into two sections.
Some air is directed to the APU compressor and the rest cools the APU
compartment.
What are paremeters of APU generator?
3-phase, 115V, 400 HC AC generator
How is fuel provided to APU with engines off?
By suction feed, controlled by the ECU and fuel control unit
How is fuel provided to APU with engines ON?
Left engine fuel ejector pump, and if AC boost pumps are operating
What is needed to start the APU?
The APU requires either the Transformer Rectifier Unit 3 (TRU 3) when
external AC power is available, or both batteries for starting.
How is energy split when only batteries are used for Engine start with APU?
When the batteries are used to start the APU, battery 1 powers the ECU while battery 2 turns the APU starter.
Describe APU start sequence with ground power available
- Commands an APU BITE test,
- Opens the APU inlet door,
- Opens the APU fuel shutoff valve,
- Turns on the left AC fuel boost pump (on the ground with left engine
off and AC power available), and - Begins the APU start sequence begins and APU IN START shows in EICAS
APU star limitations?
Max 3 times per hour, with 2 minuted between each start. ECU will prevent APU start if APU RMP is above 7%.
How long is the APU colldown before APU dorr closes?
60 seconds
What causes ECU to shutdown APU in air and on ground?
Where is APU bleed shutoff switch located?
Air Panel on Overhead panel
Can APU generator be disconnected to the Electrical system?
Yes, witht he APU GEN switch on the ELECTRICAL overhead panel
When is APU FAIL displayed?
IF APU Fails to start
IF BITE test fails
IF APU fire is detected on ground (in this case EICAS SHUTDOWN)
IF AOU fire detection fails ground
Does APU FAIL light extinguish if APU is shut down?
Yes
What is APU GCU?
APU generator control unit
What does the APU Fire switch do?
- closes APU shutoff valve
- closes APU bleed air valve
- deactivates APU generator
- commands APU shutdown
- arms APU extinguisher bottle
When the aircraft is on the ground or in flight, and a critical ECU fault occurs, the APU will
Shut down immediately
if no AC power available or the left engine is not operating, fuel is supplied to the APU by
Suction feed
when the left engine is operating, Fuel is supplied to the APU by
The left engine main fuel ejector pump
The main purpose of the APU is to provide an alternate source of
Bleed air during ground and flight operations and AC electrical power
The APU can be started with which of the following power sources?
External power
Both aircraft batteries
AC power through transformer rectifier unit 3 (TRU 3)
Which of the following conditions will cause the APU to shutdown automatically on the ground or in flight?
Failed/slow/hot/hung start
Select the three conditions that illuminate the APU FAIL light.
Failed start
Failure of built-in-test
APU fire detection fails on the ground
When the APU rotary switch is placed to the START position for three seconds:
The APU fuel shutoff valve opens
What controls the APU inlet door position?
Electronic control unit (ECU)
The main purpose of the APU is to provide an alternate source of ____. (Select two responses.)
bleed air during ground and flight operations.
AC electrical power.
When does the electronic control unit (ECU) initiate an automatic shutdown in flight?
When a critical ECU fault occurs (i.e. loss of DC power)
How is APU oil cooled?
By an air/oil heat exchanger
Does APU FAIL light stay on when APU is swithced off?
No
What type of power APU can generate?
APU can generate 75 kVA AC
Important note for LAND 2 operations and NAV sources?
NOTE: Manual tuning all of the navigation sources and setting the inbound courses is required for LAND 2 operations.
How is fuel provided to the APU?
1) if engines are running?
2) if AC Power not available?
