The oil pressure indicator measures oil pressure in psi at the delivery side of the oil
pump. The oil pressure transmitter is mounted just above the oil temperature bulb on the accessory
The turbine tachometer registers compressor turbine speed (N1) as a percentage of
maximum rpm. Propeller shaft speed is registered in hundreds of rpm. The tachometer-generator for
the N1 is mounted at the 5 o'clock position on the accessory gearbox and is driven from the internal
scavenge pump. The propeller tachometer-generator (N2) is mounted on the right side of the reduction
generators produce their own electrical current.
The torquemeter indicating system registers engine output power in psi of torque. The
transmitter converts oil pressure to an electrical signal that registers engine torque on a gage in the pilot's
The Pratt and Whitney T74-CP-702 has four major engine systems. The compressor bleed-
air system prevents the compressor from stalling during low engine speeds. Compressor bleed-air is also
used for bearing compartment seals and turbine cooling.
The lubrication pressure system produces a constant supply of clean oil to the engine
the oil tank by the internal and external scavenge pumps.
The basic fuel system consists of a single engine-driven pump, fuel control unit, temperature
compensator starting control, fuel manifold, and 14 simplex fuel nozzles. The fuel control determines
the fuel flow to the engine to produce the power required. The temperature compensator sends an air
pressure signal to the fuel control to prevent compressor stall or excessive turbine temperature. The
starting control permits the primary manifold to fill for engine starts. The fuel manifold delivers fuel to
two sets of seven simplex nozzles.
The glow plug ignition system is capable of quick light-offs at extremely low ambient
temperature. The fuel is vaporized and ignited by the hot coil element in the glow plug. The engine is