6-4. Fuel System Tubes - Removal, Cleaning, and Installation - Continued
Fuel System Tubes
Use the following criteria to determine
extent of damage:
a. Kinks or dents which could obstruct fuel
or air flow. Dents in fuel line are allowable
up to 0.015 in. (0.38 mm). Dents in
pneumatic air lines are allowable up to 1/8
in. (3 mm), no sharp radius dents allowed.
b. Cracked or broken tubes or coupling nuts.
c. Cross-threaded, crushed, or otherwise
damaged coupling nuts.
d. Chafing within clamp areas in excess of
0.010 in. deep (0.25 mm). Chafing is not
allowed at or near the flared tubing end.
e. Nicks which exceed 0.010 in. (0.25 mm
f. Inspect tubes for cracks using a 10x
magnifying glass (Appendix C). Pay
particular attention to the flared ends of the
tubes for cracks and to the areas beneath the
floating ferrules for excessive fretting
Excessive fretting is present when the
ferrule has chafed the tube sufficiently
to wear a step in the tube that can be
felt with a thumbnail or other
Failure to properly install, align
and torque fuel, oil, air fittings
and tubes could result in an
Observe precautions listed in
REMOVAL when installing fuel
Inspect and reject tubes
for damage. Observe
given wear limits.
Inspect tubes for cracks
using a 10x magnifying
glass (Appendix C). Tubes
found to contain cracks
and/or fretting damage
are to be replaced by new
parts of the same part
number as removed.