Chapter 14: APU Flashcards
what does an APU provide?
electrical power for systems
pneumatic power for aircon & start up of engine
is APU considered a essential or non-essential equipment under normal conditons?
non-essential
on which type of aircraft can APU be started mid-flight?
ETOPS rated aircraft
what is ETOPS?
extended range twin-engine operational performance standards
what does ETOPS do?
permits diversion time limit of 60 minutes
time needed to fly at single-engine speed to an alternate route
what are the 3 subsystems powered by the APU?
1) Environmental Control System (ECS)
2) Main Engine Starting (MES)
3) AIr Turbine Motor (ATM)
load section vs power section in APU
load: consist of electrical generator & load compressor for powering the 3 subsystems (ECS, MES, ATM)
power: consist of gas turbine engine that provide torque to drive load section
key components of APU
1) IGV
2) load valve
3) surge control valve
4) accessory gearbox
5) inlet door
purpose of IGV in APU
position the IGV to satisfy aircraft pneumatic load demands
purpose of IGV actuator
regulate opening of IGV for varying pneumatic load supply
how does the IGV actuator work?
controlled by ECB, operated by fuel pressure IGV varies load without change in RPM
what does the load valve in APU do?
allows pneumatic bleed from APU to be interconnected or isolated from aircraft pneumatic systems
description of load valve of APU
butterfly type spring loaded valve, fail-safe open type
what does the surge control valve do?
spill excess air that compressor delivers but cannot be used, to protect compressor from stalling
an APU is designed to produce?
constant speed with variable load
