Definition
An auxiliary ignition system used to start older reciprocating aircraft engines fitted with magneto ignition. The system supplies battery current through a vibrator (an electromechanical interrupter) to the primary winding of one magneto, producing a rapidly pulsing voltage in the secondary winding. This pulsing high voltage delivers a long, hot spark at the spark plug while the engine is being cranked at a speed too low for the magneto to generate a reliable spark on its own.
Plain English
A starting aid that uses the airplane battery and a buzzing electrical device to make a strong, steady spark at the spark plugs while the engine is turning over slowly during start.
Context Anchor
Seen in aircraft engine starting and ignition-system discussions, especially on older piston-engine aircraft.
Derivation
A 'vibrator' here is the old electrical-engineering name for a contact that opens and closes rapidly, chopping a steady DC current from the battery into pulses. Each pulse triggers a fresh spark, which is why the system is sometimes called a 'shower of sparks' starter.
Why Pilots Care
Allows reliable engine starting on vintage aircraft where the magneto cannot yet produce sufficient voltage at low cranking speeds.
Analogy
It is like flicking a light switch on and off very fast so the steady battery power becomes a series of quick pulses.
Intuition Check
Do not read vibrator here as a general shaking device. In this aviation ignition context, it means an electrical device that rapidly interrupts battery current to help make starting sparks.
Example Sentence 1
On older piston singles, a battery and a vibrator provide the hot spark needed during engine start until the magnetos can take over at running RPM.
Example Sentence 2
Without a working battery and a vibrator the pilot could not start the engine until it had been hand-propped to sufficient RPM.