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Waiting period before sumping after refueling

Aviation Mechanic Airframe (AMA) practice question 11 of 12 on Aircraft Fuel Systems. ACS element AM.II.J.R1 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONAn aircraft has just been refueled. Why should a technician wait before draining the fuel sumps to check for water?

  1. AFuel must cool before water becomes visible
  2. BWater and sediment need time to settle
  3. CThe anti-ice additive must fully dissolve
Show the answer and explanation

Correct answer: B. Water and sediment need time to settle

  • A — incorrect Cooling is not the reason; entrained water shows as cloudiness regardless, and the issue is that contaminants have not yet reached the drain.
  • B — correct Time is required for water and sediment to reach the drain point, so the sumps should be checked a period of time after fueling.
  • C — incorrect Anti-ice additive dissolves in free water to lower its freezing point; its mixing time is not the reason for delaying a sump check.

BACKGROUND

Water is the most common contaminant in aircraft fuel, and it can be dissolved in the fuel or entrained in it. Entrained water gives the fuel a cloudy appearance, with the cloudiness toward the bottom of the tank as the water settles, while air causes a similar cloudiness nearer the top. Water enters largely through condensation of vapor in the space above the liquid fuel and normally sinks into the sump, where it can be drained before flight, but this takes time. On some aircraft a large amount of fuel must be drained before settled water reaches the drain valve, so knowing the sump behavior of a particular aircraft matters. Fuel below freezing may hold entrained water as ice that will not settle into the sump until it melts.

STUDY TIP

Link every sumping question to settling time and to the fact that the sump is the low point where water and sediment collect.

KEY POINTS

  • Water is the most common fuel contaminant and enters mainly by condensation.
  • Allow settling time after fueling before checking the sumps.
  • Entrained water shows as cloudiness low in the tank; air clouds the top.

SOURCES

  • sources/ama-airframe/ch14.txt, "Checking for Fuel System Contaminants" / "Water"
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MORE ON AIRCRAFT FUEL SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.