Fluid Lines and Fittings Test Questions Answered Correctly Latest Update 2025-2026
What are aircraft fluids lines usually made of? - Answers Metal tubing or flexible hose
What type of tubing is used in stationary applications and where long, relatively straight runs are
possible? - Answers Metal tubing
What type of hose is generally used with moving parts or where the hose is subject to
considerable vibration? - Answers Flexible hose
In the early days of aviation, what type of tubing was used extensively in aviation fluid
applications? - Answers Copper
Replacement tubing should be of the same ___ and ____ as the original tubing? - Answers size
and material
Tubing made from 1100H14 (1/2-hard) or 3003H14 (1/2-hard) is used for general purpose lines
of _____ or _____ fluid pressures, such as instrument lines and ventilating conduits - Answers
Low or negligible
What type of lines are used where there is risk of FOD; Example: landing gear and wheel well
areas - Answers Steel
What type of tubing and fittings should you NOT use is any oxygen system assembly? - Answers
Titanium
Before making repairs to any aircraft tubing, it is important to make accurate ____ of tubing
______ - Answers Identification of tubing materials
What is typically printed on all rigid tubing? - Answers The tube diameter
If the code markings are hard or impossible to read, it may be necessary to test samples of the
material for ____ by____ testing - Answers hardness by hardness
Metal tubing is sized by ____ diameter, which is measured fractionally in _____ of an inch -
Answers outside; 16ths
The wall thickness of the tubing is typically printed in what? - Answers thousands of an inch
How do you determine the inside diameter of the tube? - Answers Subtract twice the wall
thickness from the outside diameter
If a fluid line assembly is to be replaced, the _____ can often be salvaged - Answers fittings
What is the four processes that tube forming consists of? - Answers Cutting, Bending, Flaring,
Beading
What percent should a new piece of tubing be cut longer than the tube to be replaced - Answers
, 10%
A small amount of flattening in bends is acceptable, but the small diameter of the flattened
portion must not be less than _____% of the original outside diameter - Answers 75%
Excessive flattening will cause what? - Answers fatigue failure of the tube
What two kinds of flares are generally used in aircraft tubing? - Answers Single flare and double
flare
What are all AN steel fittings colored? - Answers Black
What are all AN aluminum fittings colored? - Answers Blue
What does a flared tube fitting consist of? - Answers a sleeve and a nut
What do you not use on oxygen lines? - Answers lubricants
Depending of the type and use, what two types of threads will fittings have? - Answers pipe or
machine
Lines containing physically dangerous materials, such as oxygen, nitrogen, or Freon, may be
marked with what? - Answers PHDAN
Lines containing toxic materials will be marked with what? - Answers TOXIC
Lines conveying fuel may be marked with what? - Answers FLAM
Fluid lines in aircraft are often identified by markers made up of what? - Answers color codes,
words, and geometric symbols
The hand bending tool is used with tubing having ____ inch to ____ inch outside diameter -
Answers 1/4' to 1'
What type of tube assemblies should be preset with the proper size presetting tool or operation?
- Answers Flareless
MS flareless fittings are designed primarily for ______ pressure hydraulic systems that may be
subjected to severe vibrations or fluctuating pressure - Answers high
What three parts do the MS fittings consist of? - Answers body, sleeve, nut
What are standard fittings with a cryogenic sleeve? - Answers Cryofit
Scratches or nicks not deeper than _____ % of the wall thickness in aluminum alloy tubing, which
are not in the heel of a bend, may be repaired by burnishing - Answers 10%
A dent of less than _____ % of the tube diameter is not objectionable, unless it is in the heel of
What are aircraft fluids lines usually made of? - Answers Metal tubing or flexible hose
What type of tubing is used in stationary applications and where long, relatively straight runs are
possible? - Answers Metal tubing
What type of hose is generally used with moving parts or where the hose is subject to
considerable vibration? - Answers Flexible hose
In the early days of aviation, what type of tubing was used extensively in aviation fluid
applications? - Answers Copper
Replacement tubing should be of the same ___ and ____ as the original tubing? - Answers size
and material
Tubing made from 1100H14 (1/2-hard) or 3003H14 (1/2-hard) is used for general purpose lines
of _____ or _____ fluid pressures, such as instrument lines and ventilating conduits - Answers
Low or negligible
What type of lines are used where there is risk of FOD; Example: landing gear and wheel well
areas - Answers Steel
What type of tubing and fittings should you NOT use is any oxygen system assembly? - Answers
Titanium
Before making repairs to any aircraft tubing, it is important to make accurate ____ of tubing
______ - Answers Identification of tubing materials
What is typically printed on all rigid tubing? - Answers The tube diameter
If the code markings are hard or impossible to read, it may be necessary to test samples of the
material for ____ by____ testing - Answers hardness by hardness
Metal tubing is sized by ____ diameter, which is measured fractionally in _____ of an inch -
Answers outside; 16ths
The wall thickness of the tubing is typically printed in what? - Answers thousands of an inch
How do you determine the inside diameter of the tube? - Answers Subtract twice the wall
thickness from the outside diameter
If a fluid line assembly is to be replaced, the _____ can often be salvaged - Answers fittings
What is the four processes that tube forming consists of? - Answers Cutting, Bending, Flaring,
Beading
What percent should a new piece of tubing be cut longer than the tube to be replaced - Answers
, 10%
A small amount of flattening in bends is acceptable, but the small diameter of the flattened
portion must not be less than _____% of the original outside diameter - Answers 75%
Excessive flattening will cause what? - Answers fatigue failure of the tube
What two kinds of flares are generally used in aircraft tubing? - Answers Single flare and double
flare
What are all AN steel fittings colored? - Answers Black
What are all AN aluminum fittings colored? - Answers Blue
What does a flared tube fitting consist of? - Answers a sleeve and a nut
What do you not use on oxygen lines? - Answers lubricants
Depending of the type and use, what two types of threads will fittings have? - Answers pipe or
machine
Lines containing physically dangerous materials, such as oxygen, nitrogen, or Freon, may be
marked with what? - Answers PHDAN
Lines containing toxic materials will be marked with what? - Answers TOXIC
Lines conveying fuel may be marked with what? - Answers FLAM
Fluid lines in aircraft are often identified by markers made up of what? - Answers color codes,
words, and geometric symbols
The hand bending tool is used with tubing having ____ inch to ____ inch outside diameter -
Answers 1/4' to 1'
What type of tube assemblies should be preset with the proper size presetting tool or operation?
- Answers Flareless
MS flareless fittings are designed primarily for ______ pressure hydraulic systems that may be
subjected to severe vibrations or fluctuating pressure - Answers high
What three parts do the MS fittings consist of? - Answers body, sleeve, nut
What are standard fittings with a cryogenic sleeve? - Answers Cryofit
Scratches or nicks not deeper than _____ % of the wall thickness in aluminum alloy tubing, which
are not in the heel of a bend, may be repaired by burnishing - Answers 10%
A dent of less than _____ % of the tube diameter is not objectionable, unless it is in the heel of
