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Consequence of overtightening a flared tube fitting

Aviation Mechanic General (AMG) practice question 5 of 17 on Fluid Lines and Fittings. ACS element AM.I.D.K4 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONAccording to the handbook, what may happen if a flared tube fitting is overtightened during installation?

  1. AThe tube flare may be badly damaged or completely cut off
  2. BThe line may blow out of the assembly under system pressure
  3. CThe seal improves because the flare is compressed more tightly
Show the answer and explanation

Correct answer: A. The tube flare may be badly damaged or completely cut off

  • A — correct The handbook states that overtightening a fitting may badly damage or completely cut off the tube flare, or ruin the sleeve or fitting nut, which is why torque wrenches and prescribed torque values are used.
  • B — incorrect Blowing out of the assembly or leaking under pressure is the consequence the handbook gives for failing to tighten sufficiently, not for overtightening.
  • C — incorrect Extra torque does not improve the seal; the metal-to-metal contact is produced by a correctly formed flare tightened to the proper torque, and overtightening damages it.

BACKGROUND

Proper torque values for flared-type fittings are given in the handbook's flared fitting data table, and fittings should always be tightened to the correct torque value when a tube assembly is installed. Overtightening a fitting may badly damage or completely cut off the tube flare, or it may ruin the sleeve or fitting nut. Failure to tighten sufficiently is also serious because the line may blow out of the assembly or leak under system pressure. The use of torque wrenches and the prescribed torque values prevents both overtightening and undertightening. A tube fitting assembly that is tightened properly may be removed and retightened many times before reflaring is necessary.

STUDY TIP

Learn both failure modes: too much torque cuts the flare, too little lets the line blow out or leak; a torque wrench guards against both.

KEY POINTS

  • Overtightening can damage or cut off the flare and ruin the sleeve or nut.
  • Undertightening can let the line blow out of the assembly or leak.
  • Torque wrenches and prescribed values prevent both, and a properly torqued fitting can be reused many times.

SOURCES

  • FAA-H-8083-30B ch09 "Rigid Tubing Installation and Inspection - Connection & Torque"
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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.