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Ignition system

The TPE331 engines used on the Conquest incorporated a high energy ignition system consisting of an engine mounted ignition exciter, two high tension cables and two igniter plugs mounted into the combustion chamber.

Ignition exciter box

Lower igniter plug and high tension cable

The ignition system is normally used automatically during the start cycle and is controlled by the respective fuel computer. It can also be used manually by the pilot during periods of very heavy rain in flight, landing on a runway with standing water and severe icing where ingestion of ice into the engine is possible.

Manual operation of the ignition system is achieved by the use of two IGNITION OVER RIDE switches that are marked ON or OFF.

Two green lights positioned above the IGNITION OVER RIDE switches will illuminate when the ignition exciter boxes have 28 VDC available for system operation. Note: Illumination of these lights does not indicate that the igniter plugs are working.

Ignition over ride switches and ignition lights.

When the ignition over ride switches are in the OFF position, the ignition system is automatically controlled by the fuel computer 10% and 60% switches during the start cycle. When the ignition over ride switches are placed in the ON position continuous operation of the ignition system will occur.

Continuous operation of the ignition system will shorten the life span of the igniter plugs so this procedure should only be used when absolutely necessary. Continuous operation of the ignition system should only be conducted in accordance with the limitations laid down in the aircraft flight manual.

Duty cycle limits for various ignition units will differ depending on part number. FLIGHT.ORG air Conquests use ignition units which have continuous use duty limits below 10° C and 1 hour on/ 1 hour off above 10°C.

Ignition unit Part No.s 868962-2 or 868962-3, 10-378400-2, -3 or-5   Duty cycle limits
1 min. ON –1 min. OFF
2 min. ON –2 min. OFF
2 min. ON –23 min.OFF
5 min. ON –55 min. OFF
Ignition unit Part No.s 868962-3 or 10-378400-5 and service bulletin carried out.   Duty cycle limits
OAT above 10° C
1 hour ON –1 hour OFF
OAT below 10°C
Continuous operation

When conducting a Manual mode start the pilot will control the function of the 10% and 60% switches for the ignition during the start cycle through the use of the START MANUAL switches.

The pilot will control the ignition system through the use of these switches during a manual mode start.

Ignition System

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