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Flare angle produced by aircraft flaring tools

Aviation Mechanic General (AMG) practice question 10 of 17 on Fluid Lines and Fittings. ACS element AM.I.D.K2 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONThe male and female dies of the flaring tool used for aircraft tubing are ground to produce a flare of what angle?

  1. A45 degrees, the same as automotive flaring tools
  2. B35 to 37 degrees
  3. C30 to 32 degrees
Show the answer and explanation

Correct answer: B. 35 to 37 degrees

  • A — incorrect A 45-degree flare is the automotive type; the handbook says under no circumstance may an automotive-type flaring tool producing a 45-degree flare be used on aircraft tubing.
  • B — correct The handbook states that the aircraft flaring tool has dies ground to produce a flare of 35 to 37 degrees.
  • C — incorrect No 30 to 32 degree flare is described; the aircraft standard is 35 to 37 degrees so the flare matches the cone of the AN fitting.

BACKGROUND

Two kinds of flares are used in aircraft tubing, the single flare and the double flare. Flares are frequently subjected to extremely high pressures, so the flare must be properly shaped or the connection leaks or fails. A flare made too small produces a weak joint that may leak or pull apart; one made too large interferes with engagement of the fitting thread and causes leakage. The flaring tool used for aircraft tubing has male and female dies ground to produce a flare of 35 to 37 degrees, and it is never permissible to use an automotive-type tool that produces a 45-degree flare. A crooked flare results from tubing that was not cut squarely, and flaws in a flare cannot be corrected by applying more torque.

STUDY TIP

Associate 37 degrees with AN flared fittings and 45 degrees with automotive tools that are forbidden on aircraft.

KEY POINTS

  • Aircraft flaring tools produce a 35 to 37 degree flare.
  • Automotive 45-degree flaring tools must never be used on aircraft tubing.
  • A flare that is too small, too large or crooked cannot be fixed with extra torque.

SOURCES

  • FAA-H-8083-30B ch09 "Tube Flaring"
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MORE ON FLUID LINES AND FITTINGS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.