SkyDrill

PHDAN marking for physically dangerous fluid lines

Aviation Mechanic General (AMG) practice question 11 of 17 on Fluid Lines and Fittings. ACS element AM.I.D.R2 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA fluid line that contains a physically dangerous material such as oxygen, nitrogen or Freon may be marked with which additional identification?

  1. ATOXIC
  2. BPHDAN
  3. CFLAM with a warning symbol
Show the answer and explanation

Correct answer: B. PHDAN

  • A — incorrect TOXIC is used in place of FLAM on lines containing toxic materials, not on lines carrying physically dangerous gases such as oxygen or nitrogen.
  • B — correct The handbook states that lines containing physically dangerous materials such as oxygen, nitrogen or Freon may be marked PHDAN.
  • C — incorrect FLAM identifies lines conveying fuel; it does not denote a physically dangerous material.

BACKGROUND

Aircraft fluid lines are identified by markers made up of color codes, words and geometric symbols that show each line's function, content and primary hazard. Most lines are marked with 1-inch tape or decals; steel tags may be used on lines 4 inches in diameter or larger, in oily environments, on hot lines and on some cold lines, and paint is used in engine compartments where tapes or tags could be drawn into the induction system. Beyond the basic markers, lines may be further identified by function (drain, vent, pressure, return) and by hazard: fuel lines may be marked FLAM, lines containing toxic materials are marked TOXIC in place of FLAM, and lines containing physically dangerous materials such as oxygen, nitrogen or Freon may be marked PHDAN. The manufacturer installs the original markers, but the mechanic is responsible for replacing them when necessary.

STUDY TIP

Group the three hazard words by what they warn of: FLAM for flammable fuel, TOXIC for toxic contents, PHDAN for physically dangerous gases like oxygen and nitrogen.

KEY POINTS

  • Fuel lines may carry FLAM; toxic lines carry TOXIC in its place.
  • Oxygen, nitrogen and Freon lines may be marked PHDAN for physically dangerous.
  • The mechanic must replace identification markers when they need renewal.

SOURCES

  • FAA-H-8083-30B ch09 "Fluid Line Identification"
Practice the Aviation Mechanic General (AMG) test →Timed 60-question exam, by ACS area, or review your misses. Free.
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.