T-34C AIRCRAFT SYSTEMS FAMILIARIZATION
shaft that drives the main oil pump. It removes oil from the compressor bearings and the bottom
of the accessory gearbox. The external scavenge pump draws oil from the reduction gearbox and
the power turbine shaft bearings.
After leaving the main oil pump, the oil is cleaned by a metal screen type oil filter located inside
the oil tank. A bypass valve allows the oil to be rerouted if the filter becomes clogged.
The oil breather is located inside the main oil tank and it vents air from the tank overboard. It
incorporates a two-way, gravity-operated valve to accommodate inverted flight.
Cooling of engine oil is accomplished by utilizing a radiator type heat exchanger located in the
accessory air intake duct. Air passing through the oil cooler removes heat from the oil and then
exits through a square opening on the lower left side of the engine cowling. There is a
temperature-sensitive bypass valve on the oil cooler that controls oil flow through the cooler.
A combination oil pressure and oil temperature indicator is located on the instrument panel in
both cockpits. The indicator uses DC power to display the pressure and temperature of the oil as
it leaves the main oil pump. It receives its signals from the oil pressure transmitter, located on
the right engine support frame and the temperature transmitter on the right side of the accessory
gearbox. The temperature portion of the gauge is graduated in 10º C increments, while pressure
is in 10 PSI increments.
Gauge is rotated 90º for ease of reading.
40 PSI @ idle (62-65% N1)
10 - 99º C
65 - 85 PSI (above 75% N1)
(The NATOPS limit for minimum oil temperature is -40º C, but the gauge only reads to a
minimum of 0º C)
The ignition system provides initial ignition (during engine start) for the fuel/air mixture in the
provide the spark. They receive power through two shielded ignition cables, from an exciter box
aircraft nominal DC current to approximately 1400 volts pulsating DC current. It is located at
the 10 o'clock position on the engine support frame. When operating, the exciter box produces
stray voltage which will be seen on the fuel flow indicator as an increase in fuel flow, i.e., a false
PT6A-25 AIR/OIL/IGNITION SYSTEMS