COOLING SYSTEMS
No external cooling systems are incorporated on this PT6A-34 engine
installation. However, the engine incorporates an extensive internal air
system which provides for sealing of the bearing compartments and for
compressor and power turbine disk cooling. For additional information
concerning the engine’s internal air systems, refer to the Pratt & Whitney
Canada PT6A-34 Maintenance Manual.
STARTING SYSTEM
The starting system consists of a starter/generator, a starter switch and
a
STARTER ON annunciation through the G1000. The starter/generator
functions as a motor for engine starting and motors the gas generator section
until the engine stabilizes at idle speed and the starter switch is returned to
the OFF position. The starter is controlled by a three position starter switch
located on the lower left portion of the instrument panel. The switch provides
selection of OFF, HI START and LO/MOTOR. The switch is spring loaded to
the OFF position and is the normal switch position except when starting or
motoring of the engine.
HI START
Starting the engine in the HI START mode will result in faster, cooler and
softer starting conditions. When the HI START mode is selected on the
starter switch, the following starting sequence is initiated through the Master
Control Unit.
1. Ignition system automatically energized.
2. One battery provides 24 volts to starter for initial motoring of the
compressor section.
3. Once the engine reaches a predetermined speed, the Master Control Unit
places the other battery in series to supply 48 volts to the starter/generator,
thus increasing the rotational speed of the starter/generator.
4. Once the engine stabilizes at idle RPM, the starter switch is returned to
the OFF position and the starter/generator is now able to function as a
generator.
LO/MOTOR
The LO/MOTOR function of the starter switch is provided for an alternate
method of starting the engine when battery condition is poor, clearing fuel
from the engine, dry-motoring of the engine for compressor washes and other
maintenance-related procedures. The ignition system is not automatically
energized when LO/MOTOR is selected, and the batteries remain in parallel
with each other to maintain 24 volts to the starter/generator while the switch
is placed in this position. An advisory annunciation is provided through the
G1000, indicating power is being supplied to the starter. Annunciation is
displayed as follows:
STARTER ON
NOTE: It is recommended to use the LO/MOTOR function to start the
aircraft for the rst ight of the day.
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