74 Ignition System

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TTP

B1-L3

ATA 74

Beech 90 Series

B2-L3

Ignition

 Ignition System

Ignition

00   General

10   Electrical Power Supply

20   Distribution

30   Switching

IGNITION - DESCRIPTION AND OPERATION

Description and Operation 

           Two types of ignition systems are available, dependent on a specific application of an engine model to a related airframe. Each system, energized from the aircraft nominal 28-volt DC supply, provides the engine with fast light-ups at all ambient temperatures. 
          One application utilizes the spark ignition system. This system consists of two spark igniters, two shielded cables and an ignition exciter which incorporates solid-state circuitry. The second application utilizes the glow plug ignition system. 
          This system consists of two glow plugs, two shielded cables and an ignition current regulator which incorporates a selectable circuit of two sets of ballast tubes.

B. Operational Check - Spark Ignition System

(1) Switch the ignition system OFF. 

CAUTION: DO NOT ALLOW THE IGNITION CABLE BRAIDING OR FERRULES TO ROTATE WHEN LOOSENING THE COUPLING NUTS. 

(2) Disconnect the coupling nut of one ignition cable from the output connector on the ignition exciter.

(3) Switch the ignition ON. 

(4) Listen at the gas generator case for a snapping sound with frequency of approximately one snap per second. Switch the ignition OFF. 

(5) Reconnect the coupling nut of the ignition cable to the ignition exciter and remove the other cable coupling nut. Repeat steps (3)and (4). 

(6) If a snapping sound is not heard on either check, replace the ignition exciter (Ref. 74-10-00) and repeat steps (1) through (5). 

(7) If a snapping sound is not heard on one check only, replace the associated spark igniter (Ref. 74-20-04) and/or the ignition cable (Ref. 74-20-00), and repeat the operational check. If the spark igniter still fails, replace the ignition exciter (Ref. 74-10-00).

C. Operational Check - Glow Plug Ignition System 

(1) Disconnect the ignition cables from the glow plugs. 

(2) Remove the glow plugs from the gas generator case and attach to the respective cable. 

(3) Switch the ignition ON. 

(4) Confirm that the glow plugs reach an acceptable orange-yellow color in approximately eight seconds. 

(5) Allow the glow plugs to stabilize to room temperature, remove the plugs from the cables and reinstall, with new copper gaskets, on the gas generator case. Tighten the glow plugs to 300 lb.in., then loosen to zero torque. Retighten to 300 to 360 lb.in. 

(6) Connect the ignition cables to the respective glow plugs. Tighten the coupling nuts of the cables fingertight plus 45 degrees.


PTP 

Beech 90 Series

B1

LOC

FOT


B2

LOC

FOT



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