15.18 APUs Flashcards
(21 cards)
is the apu free turbine or direct coupled
free turbine
what does apu supply
bleed air and electrical power
is the apu running at a constant speed or variable speed
always runs at a constant speed
is the apu affected by changes in load on the free turbine?
no
what is one of the primary requirements of apu
to achieve ETOPs certififcation
what is the starting altitude of an APU in-flight
15000-17000ft
up to what altitude can APUs operate at?
40,000ft
when is the apu usually started in-flight
during the landing phase
why is apu started during landing phase?
reduce pneumatic burden on the engines
allows the engine to keep the compressor air for reserve thrust (aborted landing, etc..)
what are the three sections of an APU
power section
bleed section
accessory gearbox section
what does the power section of an apu drive
compressor and gearbox and drives the turbine
what does the gearbox drive in an APU
all apu accessories such as fuel and oil pumps
is the fire protection in the apu, automatically activated or activated by pilot input in the flightdeck?
automatically activated fire protection system
is the apu start sequence automatic or manually operated
manually operated by switches in the flightdeck
how long is APU cool down period
varies between 0-120 seconds
can the load compressor be switched off
no bcs its fixed to rotor shaft
what can cause apu compressors to surge
bleed load changes
how can compressor surges be prevented
by bleeding off the air that is blocking the compressor discharge
where are external emergency shutdown switches located
NLG
MLG
Refueling station
