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Aircraft systems and instrumentsQuestion 643 of 934

What is preignition?

  1. The mixture fails to ignite on some cycles
  2. The mixture burns late, as it enters the exhaust
  3. The spark plug fires twice in each cycle
  4. The mixture ignites before the normal spark
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Correct answer: The mixture ignites before the normal spark

A hot spot in the chamber, such as a carbon deposit on a spark plug, often causes it. It causes power loss and high temperature.

Source: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 7: Aircraft Systems — Combustion, page 179

Practice aircraft systems and instruments

Questions last reviewed: 18 October 2026