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Aircraft systems and instrumentsQuestion 641 of 934

Which operating practice is a common cause of detonation?

  1. Using a higher fuel grade than specified
  2. Operating at low power with a rich mixture
  3. Using a lower fuel grade than specified
  4. Descending with the throttle closed
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Correct answer: Using a lower fuel grade than specified

Other causes are very high manifold pressure with low rpm, and high power with an excessively lean mixture.

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