AUXILIARY
POWER UNIT
AIRPLANE
OPERATIONS
MANUAL
2-09-05
Page
8
Code
01
REVISION 37
AOM-145/1114
APU STARTING/OPERATION
The APU starting cycle is initiated when the APU Master knob, located
on the APU control panel, is moved to the ON position. At this
moment, an EGT valid value is shown on the EICAS. On the Model T-
62T-40C14 APU, at this time, the fuel shutoff valve is energized to
open. When the Master switch is momentarily set to START, DC
power is applied to the starter-generator, which will drive the APU
compressor up to a speed high enough to obtain sufficient airflow for
combustion.
On the Model T-62T-40C11 APU, at approximately 3% rotor speed on
the ground (or 0% in flight), the ESU supplies power to the ignition unit
as well as power to open the Start Fuel Solenoid Valve, allowing fuel
to flow to the combustion chamber. At 14% rotor speed, the Main Fuel
Solenoid Valve is energized. The APU continues accelerating up to
the 70% rotor speed, when the ESU commands starter
disengagement and Start Fuel Solenoid Valve and ignition
deenergization.
On the Model T-62T-40C14 APU, at approximately 3% rotor speed on
the ground (or 0% in flight), the FADEC supplies power to the ignition
unit as well as power to open the Main Fuel Solenoid Valve, allowing
fuel flow to the combustion chamber. The APU continues accelerating
and, when rotor speed exceeds 50%, the FADEC de-energizes the
starter and at 70% rotor speed the FADEC de-energizes the ignition
exciter.
The APU acceleration continues by the APU’s own means and, 7
seconds after having reached 95% rotor speed, the Maximum Fuel
Solenoid Valve is energized (T-62T-40C11 Model) or the FADEC
energizes the Ready-to-Load (RTL) output signal (T-62T-40C14
Model), allowing electrical and pneumatic power extraction through the
starter-generator and the bleed valve, respectively.
If a failure in the control system occurs, associated with an APU
overspeed, the Model T-62T-40C11 APU will automatically shutdown
after the rotating parts reach 108% speed, while the Model T-62T-
40C14 APU will automatically shutdown after the rotating parts reach
104% speed.
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