FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesEasy
Most horizontally opposed and radial reciprocating aircraft engines use a dual ignition system with two spark plugs per cylinder. What is the primary reason for this design?
- AIt allows one magneto to be used only for engine start and the other only for cruise flight
- BIt eliminates the need for periodic magneto internal timing checks
- CIt reduces the minimum octane rating required for the fuel
- DIt increases redundancy and improves combustion by igniting the fuel-air mixture from two points simultaneously, producing more complete and efficient burning
Show answer & explanationAnswer & explanation
Correct answer: D. It increases redundancy and improves combustion by igniting the fuel-air mixture from two points simultaneously, producing more complete and efficient burning
Dual ignition provides safety redundancy (if one magneto/plug fails, the engine still runs) and improves combustion efficiency and power output by igniting the mixture from two locations, shortening flame travel distance and reducing detonation tendency.
Why the other options are wrong
- A. Both magnetos operate simultaneously throughout all phases of flight, not split by phase.
- B. Magnetos still require periodic internal timing (E-gap) checks regardless of dual ignition.
- C. Dual ignition does not change fuel octane requirements.
Dual Ignition System
An ignition system using two independent magnetos and two spark plugs per cylinder to provide redundancy and improve combustion efficiency.
- Required by certification for most aircraft engines
- Improves flame propagation and reduces detonation risk
- Provides safety if one magneto fails in flight
Memory trick: Two sparks, twice as safe, twice as smooth burn.