· When removing or installing tubing of a
installation--some are straight, while others have
various angles. The fittings secure to the tube by
pressure-operated instrument, use a
a beaded or flared joint. The beaded or upset joint
backup wrench to avoid twisting the tub-
is used in low-pressure lines. Systems that use
ing or fitting. Do not exert undue
low-pressure lines include vacuum, deicer, and
force while tightening the connection.
oil systems that use rubber hose fittings. All
high-pressure and some low-pressure lines use
Install all electrical plugs hand tight.
flared joints. Grip dies and flaring or beading
tools are used to form flared and beaded joints.
Before connecting an electrical plug to an
When working rigid tubing, you should consult
instrument, check the plug for bent or
the manuals on the beading and flaring tools to
use the tools properly.
If piping and lines are damaged, you should
and hose connections to prevent foreign mate-
replace them with new parts. To repair tubing,
rial from entering the instrument or system.
you must determine how much tubing to remove.
Some things you need to consider when deciding
how much tubing to remove include the follow-
Most instruments require little or no lubrica-
Location of the tubing
tion in the field. The shafts and bearings or
instruments are lubricated before assembly.
The extent of damage
No further lubrication is necessary until the
instrument goes to a NADEP for overhaul. Only
The most convenient location for tool
specially trained personnel perform overhaul
operations for aircraft instruments.
There is a tendency to overtighten tubing nuts
to prevent high-pressure fluid from escaping. Such
overtightening may severely damage or completely
cut off the tube flare. When you remove a tube,
Rigid and flexible tubing is extensively used
check the flare. If you find a flare with less than
in aircraft. These tubes come in many different
50 percent of its original wall thickness, reject the
sizes. Sizing is usually determined by the outside
diameter of the tube and ranges from one-eighth
In bending tubing, you must be careful to
inch to 2 inches in diameter. The type of material
prevent collapsing of the tube at the bend. When
and wall thickness determine the amount of
making bends for fluid tubing, make sure that
pressure that a tube can safely withstand. When
you use the proper bending radius. These
replacing or repairing tubing, you should use
specifications can be found in NA 01-1A-8.
caution to make sure that you use the proper type.
Bands of paint or strips of tape around the
You can find detailed information on tubing and
line near each fitting identify each rigid line in the
tubing repairs in Aircraft Structural Hardware,
aircraft. There is at least one identifying marker
in each compartment.
All lines less then 4 inches in diameter have
RIGID TUBING. --Rigid metal tubes are
identification tape on them. The exceptions to this
widely used in aircraft for fuel, oil, coolant,
are cold lines, hot lines, and lines in an oily
oxygen, instrument, and hydraulic and vent lines.
environment. Another except ion is any line in
Corrosion-resistant steel (stainless steel) and
engine compartments where there is a chance of
aluminum alloy tubing are the most commonly
the tape going into the engine intake. In these
used tubing. You may identify the basic tube
cases, and all others where you do not use tape,
material by either visual inspection or by the alloy
use paint to identify the lines.
designation stamped on the tubing.
Identification tape codes show the function,
contents, hazards, direction of flow, and pressure
Tube fittings connect tubes together and
in the fluid line. When applying these tapes, refer
connect tubes to instruments. The shape of
to MIL-STD-1247. MIL-STD-1247 standardizes
the fitting is determined by the particular