FAA Aviation Mechanic Powerplant (AMP)Ignition and Starting SystemsMedium
Some magnetos used on radial engines incorporate a retard breaker (impulse coupling alternative) mechanism. What is the purpose of the retard breaker during engine starting?
- AIt advances ignition timing to improve smoothness immediately after start
- BIt increases magneto output voltage during cranking to compensate for low RPM
- CIt fires the spark plug at a retarded position after top dead center to prevent kickback during hand or low-RPM cranking
- DIt disables the magneto ground check circuit during runup
Show answer & explanationAnswer & explanation
Correct answer: C. It fires the spark plug at a retarded position after top dead center to prevent kickback during hand or low-RPM cranking
A retard breaker provides an additional set of points that fire the ignition several degrees after top dead center during starting (low RPM), rather than at the normal advanced running position. This retarded spark prevents the engine from kicking back against the starter or hand-cranking effort.
Why the other options are wrong
- A. Retard breakers delay, not advance, timing during starting.
- B. Voltage boost during cranking is provided by impulse couplings or vibrators, not retard breakers directly.
- D. Ground check circuits are unrelated to the retard breaker mechanism.
Retard Breaker
An auxiliary set of breaker points in some magnetos that fires the spark after top dead center during starting to prevent engine kickback.
- Used mainly on radial/large engines
- Fires spark retarded (late) only during cranking
- Normal running points resume advanced timing after start
- Alternative to impulse coupling for kickback prevention
Memory trick: Retard = 'wait a moment' before sparking, so the prop doesn't punch back.