FAA Aviation Mechanic Powerplant (AMP)Ignition and Starting SystemsEasy
Before performing maintenance on a turbine engine's capacitor discharge (CD) ignition exciter unit, a technician must
- Averify that the magneto P-lead is grounded to the airframe
- Bverify the breaker point gap is within the specified tolerance
- Callow sufficient time, per manufacturer instructions, for the internal capacitor to fully discharge before handling the unit
- Dremove and inspect the spark plug gap gauge from the tool kit
Show answer & explanationAnswer & explanation
Correct answer: C. allow sufficient time, per manufacturer instructions, for the internal capacitor to fully discharge before handling the unit
CD exciter units store a high-voltage charge in an internal capacitor that can remain lethal even after the aircraft power is removed. Manufacturer instructions require a specified wait time (or a bleed-down procedure) to ensure the capacitor is discharged before the unit is opened or handled.
Why the other options are wrong
- A. P-leads and magnetos are found on reciprocating engine ignition systems, not turbine CD exciters.
- B. Breaker points exist in magnetos, not in capacitor discharge ignition exciters.
- D. Spark plug gap gauges apply to reciprocating engine spark plugs, not CD exciter maintenance.
CD Exciter Residual Energy Hazard
A capacitor discharge ignition exciter stores high-voltage energy that can remain dangerous even after the aircraft electrical system is shut down, requiring a waiting/discharge period before maintenance.
- Stored charge can be lethal even with power removed from the aircraft
- Manufacturer specifies a minimum wait time before handling the unit
- Never handle exciter leads or terminals until verified discharged
Memory trick: CD exciter holds its charge like a loaded spring — wait before you touch it.