To further prevent internal oil leakage at engine shutdown, an external sump is connected to
the scavenge oil line at the power turbine support. One magnetic chip detector plug is in the accessory
gearbox sump, and the other one is in the scavenge oil pressure line which delivers oil to the oil outlet
port on the gearbox.
A torquemeter is located on the instrument panel and is connected to a transmitter which is
part of the engine oil system. The torque indicating system converts the pressure sensed at the
torquemeter pressure port, on the front side of the accessory gearbox, into an indication in psi of engine
FUEL CONTROL SYSTEM
The fuel control system meters fuel during starting, acceleration, constant speed, and
deceleration. This control system consists of governor, accumulator and check valve, and fuel nozzle.
These components are illustrated in figure 7.11. The following subparagraphs cover each component in
the fuel system.
The fuel pump assembly consists of two spur-gear pumps, filter, filter bypass valve,
regulator valve, and two discharge check valves. As shown in figure 7.12, the fuel pumps are parallel,
that is, fuel entering the inlet port can be pumped by either pump to the outlet port. Each pump has a
separate shear point. In the event of a pump failure, the discharge check valve of the failed pump closes
to prevent reverse flow through the pump. Failure of one pump will not affect engine operation.
The fuel control (N1) is located at the 3 o'clock position on the accessory gearbox case.
The fuel control delivers metered fuel (P2 in figure 7.11) to the fuel nozzle. The gas producer fuel
control, driven by the N1 gear train, senses compressor discharge pressure (PC). The N1 fuel control lever,
positioned by the twist grip throttle, is mechanically linked to a pointer and the fuel cutoff valve. A
quadrant, shown in figure 7.13, with 0, 5, 30, and 90 degree indications is located adjacent to the pointer.
The pilot's twist grip throttle has three basic positions: cutoff is 00 to 50; ground idle is at 300, and full
open at 900. When the twist grip is moved from cutoff to ground idle during engine start, the fuel
control automatically meters fuel in response to N1 rpm. The engine starts, accelerates, and stabilizes at
ground idle rpm. Fuel flow during this phase is metered entirely by the fuel control.