2-35. ENGINE IGNITION SYSTEM.
a. The basic ignition system consists of a solid-
state ignition exciter unit, two igniter plugs, two
shielded ignition cables, pilot-controlled IGNITION
AND ENGINE START switches, and the ENG AUTO
IGN switch. Refer to Figure 2-15. Placing an
IGNITION AND ENGINE START switch to ON will
cause the respective igniter plugs to spark, igniting the
fuel/air mixture sprayed into the combustion chamber
by the fuel nozzles. The ignition system is activated
for ground and air starts, but is switched off after
combustion light up.
b. One three-position toggle switch, located on
the overhead control panel, for each engine will initiate
starter motoring and ignition in the ON position or will
motor the engine in the STARTER ONLY position.
The switches are placarded #1 ENG START and #2
ENG START to designate the appropriate engine.
The ON switch position completes the starter circuit for
engine rotation, energizes the igniter plugs for fuel
combustion, and activates the #1 or #2 IGN ON light
on the annunciator panel. At center position, the
switch is OFF. Ignition circuits are protected by two
CONTR #1 and IGNITOR CONTR #2, located on the
overhead circuit breaker panel. Starter control circuits
are protected by two 5-ampere circuit breakers,
placarded START CONTR #1 and START CONTR #2,
located on the overhead circuit breaker panel, Figure
2-36. AUTOIGNITION SYSTEM.
If armed, the autoignition system automatically
provides combustion re-ignition of either engine should
accidental flameout occur. The system is not essential
to normal engine operation, 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 #1
IGN ON or #2 IGN ON, on the annunciator panel.
Autoignition is accomplished by 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 plugs.
a. Autoignition Switches.
placarded #1 ENG START ENG AUTO IGN and #2
ENG START ENG AUTO IGN, with positions ARM
and OFF, are located on the overhead control panel,
Figure 2-15. 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 5-ampere
circuit breaker, placarded START CONTR #1 or
START CONTR #2, located on the overhead circuit
breaker panel, Figure 2-16.
b. Autoignition Lights. If an armed auto-
ignition system changes from a ready condition to an
operating condition energizing the two igniter plugs in
an engine, a corresponding green annunciator panel
light will illuminate. The annunciator panel light,
placarded #1 IGN ON or #2 IGN ON, indicates that the
igniters are energized. The auto-ignition system is
triggered from a ready condition to an operating
condition when engine torque drops below 20%.
Therefore, when an auto-ignition system is armed, the
igniters will be energized continuously during the time
an engine is operating at a level below 20% maximum
torque. Auto-ignition lights are protected by two
CONTR #1 or IGNITOR CONTR #2, on the overhead
circuit breaker panel.
2-37. 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 starter
function, 28 Vdc is required to power rotation. In
250 amperes dc output. When the starting function is
selected, the starter control circuits receive power
through the respective 5-ampere START CONTR
circuit breakers 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. For
additional description of the starter-generator system,
refer to Section IX.
2-38. ENGINE INSTRUMENTS C D .
Engine instruments are vertically mounted near
the center of the instrument panel, Figure 2-17.
a. Turbine Gas Temperature Indicators. Two
TGT gauges on the instrument panel are calibrated in
degrees Celsius. Each gauge is connected to
thermocouple probes located in the hot gases between
wheels. The gauges register the
temperature present between the compressor turbine
and power turbine for the corresponding engine.
b. Engine Torquemeters. Two torquemeters
on the instrument panel indicate torque applied to the
propeller shafts of the respective engines, Figure 2-14.
Each gauge shows torque in percent of maximum
using 2% graduations and is actuated by an electrical
signal from a pressure sensing system located in the