Aircraft systems and instrumentsQuestion 660 of 934

Why should a pilot fill the fuel tanks after the last flight of the day?

  1. To increase the octane rating of the fuel
  2. To prevent moisture condensing in the tank
  3. To lower the fuel temperature overnight
  4. To keep the fuel vents free of ice
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Correct answer: To prevent moisture condensing in the tank

The pilot should also avoid refueling from cans and drums to prevent fuel contamination.

Source: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 7: Aircraft Systems — Fuel Systems — Fuel Contamination, page 188

Practice aircraft systems and instruments

Questions last reviewed: 18 October 2026