FAA Aviation Mechanic Powerplant (AMP)Ignition and Starting SystemsHard
An aircraft engine is equipped with a single dual magneto (one housing containing two independent sets of breaker points, coils, and distributors) rather than two separate magnetos. What is the primary advantage this design provides?
- AIt eliminates the need for two spark plugs per cylinder, reducing ignition system weight
- BIt provides ignition redundancy with two independent firing circuits in a single housing, saving weight compared to two full magnetos
- CIt allows the engine to run on only one spark plug per cylinder during normal operation
- DIt eliminates the need for an ignition switch since both circuits operate independently at all times
Show answer & explanationAnswer & explanation
Correct answer: B. It provides ignition redundancy with two independent firing circuits in a single housing, saving weight compared to two full magnetos
A dual magneto houses two completely independent ignition circuits (separate coils, breaker points, and distributors) in one case, still firing two spark plugs per cylinder for redundancy, but saving the weight and space of two separate magneto housings and drive mechanisms.
Why the other options are wrong
- A. Dual magnetos still fire two plugs per cylinder for redundancy.
- C. Both circuits still operate to fire both plugs; single-plug operation isn't the design intent.
- D. An ignition switch is still required to select/ground the circuits.
Dual Magneto
A single magneto housing containing two independent sets of breaker points, coils, and distributor components, providing the redundancy of two magnetos with reduced weight and a single drive.
- Still fires two spark plugs per cylinder for redundancy
- Failure of one internal circuit does not disable the other
- Used on some high-performance/aerobatic and certain light aircraft engines
Memory trick: Dual magneto = 'two hearts, one body' — redundancy without extra weight