Definition
A condition in a magneto or other contact-breaker ignition system in which the breaker points fail to close cleanly after opening, instead rebounding open one or more times before settling. This rapid open-close-open behavior occurs at high engine speeds when the spring tension holding the points closed cannot react fast enough to keep up with the cam, and it disrupts the timing and strength of the spark delivered to the cylinders.
Plain English
The small metal contacts inside the magneto are supposed to snap shut firmly each time the cam lets them go. At high engine speeds they can bounce instead of closing cleanly, like a screen door that doesn't quite latch on the first swing. When that happens, the spark to the cylinders becomes weak or mistimed.
Context Anchor
Seen in piston-engine ignition system maintenance, especially when inspecting or troubleshooting magnetos and rough engine operation.
Derivation
Breaker points are the small contacts that 'break' the primary electrical circuit inside a magneto to trigger a spark. 'Bounce' is used in its ordinary mechanical sense -- a part rebounding instead of staying put. The name simply describes what is happening: the points are bouncing instead of closing.
Why Pilots Care
It leads to unreliable ignition, rough engine operation, and potential in-flight power loss if not corrected during maintenance.
Analogy
It is like flipping a light switch that should click once, but the contact inside chatters several times before settling. The result is not a clean on-or-off action.
Intuition Check
This does not mean the aircraft or engine is physically bouncing. It means the small electrical contact inside the ignition system is rebounding or chattering when it should move cleanly.
Example Sentence 1
The mechanic suspected breaker-point bounce after the engine ran smoothly at cruise but stumbled during the high-RPM magneto check.
Example Sentence 2
Replacing the worn breaker points eliminated the bounce and restored smooth ignition timing.