Figure 3-3. Ignition System

CHAPTER THREE

T-34C AIRCRAFT SYSTEMS FAMILIARIZATION

CHANGE 3

WORKBOOK

Figure 3-3 Ignition System

There is an ignition switch located on the right subpanel of each cockpit which is labeled

IGNITION ON/HOLD OFF. The switch is spring-loaded to the ON position, allowing current

flow to the exciter when the starter switch is turned on. The HOLD OFF position momentarily

interrupts current to the exciter, allowing the engine to be motored without initiating combustion.

The starter switch, also on the right subpanel of each cockpit, is labeled STARTER ON/OFF.

This switch, which is not spring loaded, allows power (battery or GPU) to actuate the ignition

system. A green IGNITION annunciator light located on the annunciator panel in both cockpits

illuminates to indicate when the exciter is energized.

The autoignition system automatically provides a spark for combustion in the event of an engine

"flameout." The system is normally armed prior to any aerobatic flight maneuvers or during

flight in foul weather conditions. The autoignition switch located adjacent to the ignition switch

is a two-position switch and, when turned on, arms the system. The normal position is OFF

because the system is not essential to normal engine operation. Located on the reduction

gearbox is an autoignition sense switch, which allows current flow to the exciter if engine output

power drops into the 300 - 180 ft-lbs. range. Therefore, with the system armed, once the system

is triggered to an operating condition, the igniters will fire continuously until torque is increased

above the 180 - 300 ft-lbs. range. A green AUTO IGN annunciator light in each cockpit

illuminates when the system is armed. When the system changes to an operating condition, the

AUTO IGN light extinguishes and the IGNITION light illuminates.

3-6 PT6A-25 AIR/OIL/IGNITION SYSTEMS