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Classifying a fuel leak by wetted area

Aviation Mechanic Airframe (AMA) practice question 9 of 12 on Aircraft Fuel Systems. ACS element AM.II.J.K7 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONA fuel leak area is wiped dry, and 30 minutes later the collected fuel covers a circle about 2 inches in diameter. How is this leak classified?

  1. ASeep, since it is under 4 inches
  2. BRunning leak
  3. CHeavy seep
Show the answer and explanation

Correct answer: C. Heavy seep

  • A — incorrect A seep covers ¾ to 1½ inches in diameter, so a 2-inch area is past that range.
  • B — incorrect A running leak pools and actually drips from the aircraft, often following the contour of the airframe for a long distance.
  • C — correct Heavy seeps form an area from 1½ inches to 4 inches in diameter in 30 minutes, which covers a 2-inch circle.

BACKGROUND

Four classifications describe aircraft fuel leaks: stain, seep, heavy seep, and running leak. The standard is the surface area of the collected fuel 30 minutes after the area is wiped dry. Less than ¾ inch in diameter is a stain; ¾ to 1½ inches is a seep; 1½ to 4 inches is a heavy seep; and a running leak pools and drips from the aircraft. When fuel leaks into an area where vapors can collect, the leak must be repaired before flight because of the fire and explosion potential. Repair of an external leak that is not in danger of being ignited may be deferred, but the source should still be found and monitored so it does not worsen.

STUDY TIP

Memorize the three diameter breakpoints as ¾, 1½, and 4 inches, and remember the timing is always 30 minutes after wiping dry.

KEY POINTS

  • Leak size is judged by wetted diameter 30 minutes after wiping dry.
  • Stain is under ¾ inch, seep ¾ to 1½ inches, heavy seep 1½ to 4 inches.
  • A running leak pools and drips from the aircraft.

SOURCES

  • sources/ama-airframe/ch14.txt, "Fuel Leak Classification"
Practice the Aviation Mechanic Airframe (AMA) test →Timed 100-question exam, by ACS area, or review your misses. Free.
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.