tion, but is used to reduce the possibility of power loss
due to icing or other conditions. Each engine has a
separate autoignition control switch and a green indicator
light placarded No.1 IGN ON or No.2 IGN ON, on the
energizing the two igniter plugs in each engine.
The system should be turned OFF
during extended ground operation
to prolong the life of the igniter
Autoignition Switches. Two switches, located on
the overhead control panel (fig. 2-12), placarded ENG
AUTO IGN-ARM control the autoignition systems. The
ARM position initiates a readiness mode for the
autoignition system of the corresponding engine. The
OFF position disarms the system. Each switch is
protected by a corresponding START CONTR No.1 or
No.2 5ampere circuit breaker on the overhead circuit
breaker panel (fig. 2-27).
Autoignition Lights. If an armed autoignition
system changes from a ready condition to an operating
condition (energizing the igniter plugs in the engine) a
illuminate. The annunciator panel light is placarded No.1
IGN ON or No.2 IGN ON and indicates that the igniters
are energized. The autoignition system is triggered from
a ready condition to an operating condition when engine
torque drops below approximately 20%. Therefore, when
an autoignition system is armed, the igniters will be
energized continuously during the time when an engine is
operating at a level below approximately 20% torque.
The autoignition lights are protected by 5-ampere
IGNITOR CONTR No.1 or No.2 circuit breakers, located
on the overhead circuit breaker panel (fig. 2-27).
2-32. ENGINE STARTER-GENERATORS.
One starter-generator is mounted on each engine
accessory drive section. Each is able to function either as
a starter or as a generator. In the starter function, 24
volts DC is required to power rotation. In the generator
function, each unit is capable of 400 amperes DC output.
When the starting function is selected, the starter control
circuit receives power, through the respective 5-ampere
START CONTR circuit breaker on the overhead circuit
breaker panel, from either the aircraft battery or an
external power source. When the generating function is
selected, the starter-generator provides electrical power.
An automatic starter cutoff control is installed in each
starter-generator to provide automatic termination of the
start cycle when engine speed reaches 44% NI. Engine
speed is sensed by a magnetic sensor located in the
starter-generator. For additional description of the starter-
generator system, refer to Section IX.
2-33. ENGINE INSTRUMENTS.
The engine instruments are vertically mounted near
the center of the instrument panel (fig. 230).
Turbine Gas Temperature Indicators. Two TGT
gages on the instrument panel are calibrated in degrees
Celsius (fig. 2-30). Each gage is connected to
thermocouple probes located in the hot gases between
the turbine wheels. The gages register the temperature
present between the compressor turbine and power
turbine for the corresponding engine.
Engine Torquemeters. Two torquemeters on the
instrument panel indicate torque applied to the propeller
shafts of the respective engines (fig. 2-30). Each gage
shows torque in percent of maximum using 2 percent
graduations and is actuated by an electrical signal from a
pressure sensing system located in the respective
propeller reduction gear case. Torquemeters are
protected by individual. 0.5-ampere circuit breakers
placarded TORQUE METER No.1 or No.2 on the
overhead circuit breaker panel (fig. 2-27).
Turbine Tachometers. Two tachometers on the
instrument panel register compressor turbine RPM (N1)
for the respective engine (fig. 2-30). These indicators
register turbine RPM as a percentage of maximum gas
generator RPM. Each instrument is slaved to a
tachometer generator attached to the respective engine.
Oil Pressure/Oil Temperature Indicators. Two
gages on the instrument panel register oil pressure in PSI
and oil temperature in °C (fig. 2-30). Oil pressure is taken
from the delivery side of the main oil pressure pump. Oil
temperature is transmitted by a thermal sensor unit which
senses the temperature of the oil as it leaves the delivery
side of the oil pressure pump. Each gage is connected to
pressure transmitters installed on the respective engine.
Both instruments are protected by 5-ampere circuit
breakers, placarded OIL PRESS and OIL TEMP No.1 or
No.2, on the overhead circuit breaker panel (fig. 2-27).
Change 2 2-27