SkyDrill

Output of the shower of sparks starting vibrator

Aviation Mechanic Powerplant (AMP) practice question 9 of 11 on Ignition and Starting Systems. ACS element AM.III.H.K3 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONIn a shower of sparks ignition system, what does the starting vibrator deliver to the magneto?

  1. APulsating direct current to the primary coil
  2. BHigh ignition voltage to the distributor rotor
  3. CA steady direct current to the secondary coil
Show the answer and explanation

Correct answer: A. Pulsating direct current to the primary coil

  • A — correct The vibrator changes the battery's direct current into pulsating direct current and delivers it to the primary coil of the magneto.
  • B — incorrect Unlike the booster coil, the starting vibrator does not produce the high ignition voltage within itself.
  • C — incorrect Steady current would produce no changing field; the vibrator points interrupt the current many times per second, and the current goes to the primary.

BACKGROUND

The shower of sparks system, built around a high-tension retard breaker magneto and a starting vibrator, provides several sparks at the spark plug electrodes during starting. The starting vibrator consists of an electrically operated vibrator, a condenser, and a relay mounted on a base plate in a metal case. Current through the vibrator coil opens the vibrator points, the field collapses, the points reclose, and the cycle repeats many times per second, producing an audible buzz. Each time the points close, pulsating direct current reaches the magneto primary, and the rapidly building and collapsing field induces a rapid succession of voltages in the secondary, which becomes a shower of sparks at the selected plug.

STUDY TIP

Remember the one-line distinction: the booster coil makes its own high voltage, the starting vibrator only chops battery current into pulses for the magneto primary.

KEY POINTS

  • The starting vibrator sends pulsating DC to the magneto primary coil.
  • It does not generate high ignition voltage itself.
  • Rapid interruptions produce a shower of sparks at the plug gap.

SOURCES

  • sources/amp-powerplant/ch04.txt "High-Tension Retard Breaker Vibrator"
Practice the Aviation Mechanic Powerplant (AMP) test →Timed 100-question exam, by ACS area, or review your misses. Free.
MORE ON IGNITION AND STARTING SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.