Metallines. Metal lines usually are made of stainless steel or an aluminum alloy. Check for leaks, loose
anchorages, scratches, kinks, or other damage when inspecting.
Flexible hose. Flexible hose is made of synthetic rubber or Teflon. Special heat-resistant hose is used
where the flexible lines will be subjected to intense heat. Fire-resistant hose is used for all fuel lines in the engine
compartment. Check for leakage, looseness, cracks, or other damage when inspecting.
Removal and installation. Refer to TM 1-1500-204-23-2 for detailed information on fabrication, removal,
and installation of fuel lines. General procedures are described in the following paragraphs.
Compatibility of fittings. All fittings are to be compatible with their mating parts. Although various
types of fittings appear to be interchangeable, in many cases they have different thread pitch or minor design differences
which prevent proper mating and may cause the joint to leak or fail.
Routing. Make sure that the line does not chafe against control cables, airframe structure, etc., or
come in contact with electrical wiring or conduit. Where physical separation of the fuel lines from electrical wiring or
conduit is impracticable, locate the fuel line below the wiring and clamp it securely to the airframe structure. In no case
may wiring be supported by the fuel line.
Alignment. Locate bends accurately so that the tubing is aligned with all support clamps and end
fittings and is not drawn, pulled, or otherwise forced into place by them. Never install a straight length of tubing between
two rigidly mounted fittings. Always incorporate at least one bend between such fittings to absorb strain caused by
vibration and temperature changes.
Bonding. Bond metallic fuel lines at each point where they are clamped to the structure. Integrally
bonded and cushioned line support clamps are preferred to other clamping and bonding methods.
Support of line units. To prevent possible failure, all fittings heavy enough to cause the line to sag
should be supported by means other than the tubing.
Support clamps. Rubber cushioned clamps should be installed in a manner to ensure ¼
minimum clearance between aircraft structure and fuel lines. They should be Installed so that the weight of the line tends
to tighten attaching hardware. Support clamps should be spaced as shown in table 2-4 or, if near a bend, as close as
possible to reduce overhang as shown in figure 2-3.
Table 2-4. Support Clamp Spacing
Figure 2-3. Clamp Location for Tube Bends