shunted surface gap spark igniter. The system is powered by the aircraft 28-volt dc electrical system.
This ignition system is only required during starting, because continuous combustion takes place after the
engine is started. Components of the ignition and turbine outlet temperature (TOT) systems are
illustrated in figure 7.16.
The TOT thermocouple harness contains four probes used to sense the temperature of the
gases on the outlet side of the gas-producer turbine rotor. Each thermocouple probe generates a dc
millivoltage which is directly proportional to the gas temperature it senses. The thermocouple harness
averages the four voltages produced and indicates TOT on a gage in the cockpit.
The Allison T63 is a free-power gas turbine engine which has four major sections: the
compressor assembly, power and accessory gearbox, turbine assembly, and combustion assembly. The
power-turbine governor senses power turbine speed and relays this to the fuel control that controls the
compressor speed. The fuel control sends fuel to the nozzle located in the combustion section, and the
nozzle sprays fuel into the combustion liner.
The engine is lubricated by a dry-sump pressure system. Ignition for engine starting comes
from an ignition exciter and spark igniter located next to the fuel nozzle in the engine combustion