Turbine Engine Ignition System Maintenance

Maintenance of a typical turbine engine ignition system consists primarily of inspection, testing, troubleshooting, removal, and installation of ignition system components.

Inspection

Inspection of the ignition system normally includes the following:

1. Inspect ignition lead terminals. The ceramic terminal should be free of arcing, carbon tracking, and cracks.
2. Inspect the grommet seal. It should be free of flashover and carbon tracking. [Figure 1]



Figure 1. Flashover inspection

3. The wire insulation should remain flexible with no evidence of arcing through the insulation.
4. Inspect the complete system for secure component mounting, electrical shorts, high-voltage arcing, and loose connections.

Check System Operation

The igniter can be checked by listening for a snapping noise as the engine begins to turn, driven by the starter. Although the following procedure is not commonly used and should only be performed when specified by the applicable maintenance manual, the igniter can also be checked by removing it and activating the start cycle while observing for a spark across the igniter gap.

Caution: The high energy level and voltage associated with turbine ignition systems can cause injury or death to personnel who come into contact with an energized ignition system.

Repair

Tighten, secure, and safety-wire components as required, and replace any faulty wiring or defective ignition system components.

Removal, Maintenance, and Installation of Ignition System Components

The following instructions are typical procedures suggested by many gas turbine manufacturers. These instructions are applicable to the engine ignition components. Always consult the applicable manufacturer’s instructions before performing any ignition system maintenance.

Ignition System Leads

1. Remove the clamps securing the ignition leads to the engine.
2. Remove safety wire and disconnect electrical connectors from exciter units.
3. Remove safety wire and disconnect lead from igniter plug.
4. Discharge any electrical energy stored in the system by properly grounding the ignition circuit, then remove the ignition leads from the engine.
5. Clean leads with approved dry cleaning solvent.
6. Inspect connectors for damaged threads, corrosion, cracked insulators, and bent or broken connector pins.
7. Inspect leads for worn or burned areas, deep cuts, fraying, and general deterioration.
8. Perform a continuity check of the ignition leads.
9. Reinstall leads, reversing the removal procedure.

Igniter Plugs

1. Disconnect ignition leads from igniter plugs. Before disconnecting the ignition lead, disconnect the low-voltage primary lead from the ignition exciter unit and wait at least one minute to allow the stored energy to dissipate before disconnecting the high-voltage cable from the igniter.
2. Remove igniter plugs from mounts.
3. Inspect the igniter plug firing-end surface and electrode gap. Before inspection, remove residue from the shell exterior using a dry cloth. Do not remove any deposits or residue from the firing end of the low-voltage igniters. High-voltage igniters can have the firing end cleaned to aid in inspection. [Figure 2]



Figure 2. Firing end cleaning

4. Inspect for fretting of igniter plug shank.
5. Replace any igniter plug whose firing surface is granular, chipped, or otherwise damaged.
6. Replace dirty or carbonized igniter plugs.
7. Install igniter plugs in mounting pads.
8. Check for the specified clearance between the combustion chamber liner and the igniter plug.
9. Tighten igniter plugs to manufacturer’s specified torque.
10. Safety wire igniter plugs.

Quick Review: Turbine Ignition System Inspection & Maintenance

Why must the ignition system be discharged before disconnecting ignition leads?

Turbine engine ignition systems use capacitors that can retain a high-voltage electrical charge even after electrical power is removed. Properly discharging the system before disconnecting ignition leads helps prevent electrical shock, protects maintenance personnel, and reduces the risk of damage to ignition components.

Why is continuity testing important for turbine engine ignition leads?

A continuity test verifies that the ignition lead provides an uninterrupted electrical path between the exciter unit and the igniter plug. An open circuit or excessive resistance can prevent the delivery of sufficient ignition energy, resulting in unreliable engine starting or ignition system faults.

Why should igniter plug clearance be checked after installation?

Correct clearance ensures that the igniter plug is properly positioned within the combustion chamber and does not interfere with the combustion chamber liner or surrounding components. Maintaining the specified clearance also helps achieve reliable ignition while preventing mechanical damage during engine operation.

Why should only approved ignition system components be installed on turbine engines?

Turbine engine ignition components are designed to operate together under high voltage, vibration, and extreme temperatures. Using approved replacement parts ensures proper electrical compatibility, maintains system reliability, and helps preserve the engine's certified performance and safety standards.

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