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Aircraft systems and instrumentsQuestion 654 of 934

Why is water in the fuel sump hazardous?

  1. It can freeze and block lines, or stop the engine
  2. It dissolves the lead and lowers the fuel octane rating
  3. It corrodes the fuel tank vents quickly
  4. It makes the engine run too rich at idle
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Correct answer: It can freeze and block lines, or stop the engine

If water is in the sump, more water is probably in the tanks. The pilot should drain until no water remains.

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

Practice aircraft systems and instruments

Questions last reviewed: 18 October 2026