Definition 1 of 2
Definition
An auxiliary starting ignition system used on some reciprocating aircraft engines, in which a vibrator unit produces a continuous stream of sparks at one set of spark plugs during engine start. The vibrator interrupts battery current rapidly, sending pulsing low-voltage current through the primary winding of one magneto (the left magneto, with retarded breaker points). This produces a series of high-voltage sparks at the cylinder being fired, making starting easier and reducing the risk of kickback. Once the engine starts and the ignition switch is moved to BOTH, normal magneto operation takes over and the vibrator is disconnected.
Plain English
A starting aid that fires a rapid series of sparks at the spark plug instead of just one, making the engine easier to start. Once the engine is running, it switches off and the regular ignition takes over.
Context Anchor
Seen in aircraft piston-engine ignition systems, starting procedures, and troubleshooting when the engine cranks but is hard to start.
Derivation
Named descriptively: the vibrator unit produces a literal shower (continuous stream) of sparks at the plug during cranking, rather than the single spark per cylinder firing produced by a magneto in normal operation.
Why Pilots Care
Provides dependable starts and reduces the chance of engine kickback or hot-start issues on certain piston engines.
Analogy
It is like using several quick match strikes to light a burner instead of depending on one weak strike.
Intuition Check
Do not picture sparks spraying around the engine. The 'shower' is a rapid series of controlled electrical sparks at the spark plugs, used only during starting.
Example Sentence 1
The radial engine was equipped with a shower of sparks ignition system, so the pilot held the ignition switch in the START position until the engine fired.
Example Sentence 2
During the magneto check the mechanic confirmed the shower of sparks system produced the expected RPM drop.