all engine operating speeds. Oil pressure is controlled by the pressure relief valve. If the oil strainer
becomes clogged, a bypass valve opens permitting oil flow and allowing engine operation to continue.
Scavenge oil from the five main bearings and gearbox is scavenged by five of the six gear
stages in the main oil pump.
The first stage is a pressure pump. Stage two scavenges oil from No. 1 bearing; stage three
from No. 3 bearing; stage four from the gearbox and No. 2 bearing; stage five from No. 4 bearing; and
stage six from No. 5 bearing. The scavenge oil empties into a common tube that returns the oil to the
tank. An air-oil separator in the gearbox removes oil from the breather air. Return oil passes through a
de-aerator which removes most of the air. The oil tank contains baffles to prevent re-aeration of the oil
in the tank.
Each of the bearing compartments and the oil tank are vented to the components drive
gearbox. A rotary separator within the gearbox separates the majority of oil particles from the breather
air. This air then exits through the overboard breather connector on the upper right side of the gearbox.
The torque sensor, the ignition system, and the power turbine inlet temperature indicating
system make up the engine electrical system.
The torque sensor consists of a torque shaft assembly, a three-pole magnetic torque sensor,
and a torquemeter. It produces a visual indication of power transmitted from the engine to the main
rotor gearbox by measuring the main drive shaft twist resulting from engine torque.
The ignition circuit is energized only during the starting cycle through operation of the starter
circuit. The ignition system components consists of two identical, four-joule ignition exciters, one for
each igniter plug. The ignition system operates satisfactorily with an input voltage of 14 to 30v dc.
Operation of this system is the same as described in chapter 2, paragraph 2.22.