15.18 Flashcards
What is the apu
Small gas turbine (free) turbo shaft engine
What does the apu supply
Pneumatic bleed air and electrical power
What does the apu supply
Pneumatic bleed air and electrical power
What does the apu do on ground
Allow aircraft to operate without ground support equipment
Primary source of bleed air for engine starting
Where is the apu located
Unpressised fireproof compartment in the rear fuselage tail cone
How do you require an ETOPS certification
Have an inflight APU
Apu starting altitude
15-17k ft
Apu operation altitude
Up to 40k
Why are apus started in landing phase
Unloads main engine pneumatic burden
3 parts of apu
Power
Bleed
Accessory gearbox
Order of operation of the apu
Power drives compressor and gearbox
Gearbox drives apu accessories
Power section of GTE
Compressor
Combustion chamber
Turbine
What does the electrical control box do (ECB)
Start sequence
Turbine sped
EGT
oil and fuel supply
Bleed air outlet
What generator is used in the apu
AC
What does normal speed mode do
Keeps the apu at 100% regardless of load changes
Why does the apu monitor acceleration
Optimize apu start
Protect the apu from damage
What correlation does bleed load have with EGT
Opening the bleed valve increases bleed load which increases APU EGT
What is apu cooldown period
0-120 seconds
How many pressure switches in the primary apply fuel system
Minimum of one
What does the positive fuel pressure in the apu fuel feed line do
Prevent cavitation at the high pressure fuel pump of the APU
What does the cooling system do
Supply air to the oil cooler and apu ventilation
What 2 things must be done in order for the apu bleed valve to open
Apu bleed Switch selected on
Apu start sequence compete
What’s an advantage of an apu having a load compressor
Makes it more fuel efficient
3 parts of the load compressor
Variable inlet guide vanes
Inlet guide vane actuator
Apu control unit
When is the anti-surge system used
On apus without a load compressor
How does a anti surge system work
Anti surge valve bleeds air off when surging is possible
When does the surge control valve open
Airflow behind the load compressor decreases or stops
When is an automatic apu emergency shutdown activated
When fire condition occurs while aircraft is on the ground
What’s the quickest way to shut down the apu
Activate the fire switch
What signals are used by the apu to control a constant speed
Speed signal and torque motor signal
