Aircraft systems and instrumentsQuestion 656 of 934

The recommended fuel grade is not available. What should the pilot do?

  1. Use the next lower grade
  2. Use the next higher grade
  3. Mix two lower grades in equal parts
  4. Use automobile gasoline of equal octane
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Correct answer: Use the next higher grade

Never use a lower grade than recommended. It can cause detonation.

Source: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 7: Aircraft Systems — Fuel Systems — Fuel Grades, page 187

Practice aircraft systems and instruments

Questions last reviewed: 18 October 2026