FAA Aviation Mechanic Powerplant (AMP)Ignition and Starting SystemsMedium
A technician inspecting a high-tension magneto notices excessive wear at the distributor rotor finger and distributor block electrodes, increasing the air gap between them. What is the most significant operational effect of this wear at high altitude?
- ANo measurable effect, since distributor gap does not influence secondary voltage
- BA reduction in idle RPM due to reduced fuel flow
- CIncreased risk of flashover or misfire because higher voltage is required to jump the larger gap in less dense air
- DExtended spark plug service life from reduced current flow
Show answer & explanationAnswer & explanation
Correct answer: C. Increased risk of flashover or misfire because higher voltage is required to jump the larger gap in less dense air
The distributor gap is part of the secondary ignition circuit; voltage must jump this gap before reaching the spark plug. At altitude, lower air density reduces the dielectric strength of the air, making it easier for the spark to flash over inside the distributor rather than reach the plug when the gap is excessively worn, causing misfiring.
Why the other options are wrong
- A. Distributor gap directly affects the voltage required to fire the plug.
- B. Idle RPM is controlled by mixture and throttle, not distributor wear.
- D. Excess gap increases voltage demand and stresses the system, reducing rather than extending life.
Distributor Gap and Altitude
The gap between the distributor rotor finger and block electrode requires higher voltage to jump as it wears larger, increasing flashover risk at altitude where air is less dense.
- Part of high-tension secondary ignition circuit
- Excess wear increases required firing voltage
- Thin air at altitude reduces dielectric strength
- Can cause internal flashover instead of spark plug firing
Memory trick: Thin air + big gap = spark takes the shortcut inside.