FAA Aviation Mechanic Powerplant (AMP)Ignition and Starting SystemsEasy
A technician replaces the ignition harness on a reciprocating engine. What is the primary purpose of the metal braided shielding surrounding each ignition lead?
- ATo reduce electromagnetic interference with aircraft radios and avionics
- BTo increase the mechanical strength of the lead so it resists vibration damage
- CTo insulate the high voltage conductor from grounding out on the engine
- DTo provide a low-resistance ground path for the magneto P-lead
Show answer & explanationAnswer & explanation
Correct answer: A. To reduce electromagnetic interference with aircraft radios and avionics
The braided metal shielding around each ignition lead is grounded and acts as a Faraday shield, containing the electromagnetic radiation produced by the high-voltage spark discharge so it does not interfere with radio and navigation equipment.
Why the other options are wrong
- B. Strength is a secondary benefit; shielding's main purpose is electrical suppression.
- C. Insulation from grounding is provided by the lead's dielectric insulation, not the shield.
- D. The P-lead is a separate wire; shielding is not part of the P-lead ground circuit.
Ignition Harness Shielding
Grounded braided metal covering over each ignition lead that suppresses radio-frequency interference generated by the high-voltage spark discharge.
- Grounded at both magneto and spark plug ends
- Prevents radio/avionics interference
- Must be checked for continuity and corrosion
- Damaged shielding can cause static in radios
Memory trick: Shield = Static Shield for the radio.