RUNNING LEAK.A running leak is a fuel leak
that flows steadily.
Most aircraft structural repair manuals do not
classify a slow seep or seep in an open area (the surfaces
of the aircraft exposed to the airstream) as a flight
hazard. A slow seep or seep in an open area need not
be repaired before flight if structural integrity exists
and there is no danger of an increase in leak intensity
during flight. Slow seeps and seeps considered
acceptable for flight should be frequently inspected to
ensure the leak intensity does not increase prior to
Heavy seeps and running leaks are classified as
flight hazards, regardless of their location in the aircraft.
Any leak classified as a flight hazard must be corrected
Leaks are the most common trouble encountered
with the integral fuel cells. Slight leaks may sometimes
be repaired simply by retorquing (tightening) the bolts
or screws on either side of the leak. On others it is often
necessary to reseal the injection groove around the
perimeter of the wing, and replace the O-rings and
washers. Both of these procedures are described in the
RETORQUING.You should always retorque to
stop a fuel stain or seepage before attempting to reseal.
The first step in stopping a leak is to retorque the bolts
or screws for 6 inches on each side of the leaking area
according to the torque values given in the MIM for the
different size bolts and screws being used. Standard
bolts are used primarily in attaching wing skin and
should be torqued from the nut side according to
standard torque tables.
REPLACING SEALS.If, after retorquing, the
leak still persists around a bolt and washer seal, replace
the seal with a new one. Be sure to install a washer
between the bolt head and the seal or leakage will still
occur. Also, be sure to torque the bolts according to the
torque values listed in the MIM.
If the leak is around an O-ring seal, replace the
O-ring. First, loosen the bolt or screw with a steady
pressure. Back out the bolt only as far as necessary to
remove the O-ring over the head of the bolt or screw.
Use petrolatum (Vaseline) if desired. Install a new
O-ring and tighten the bolt to the required torque.
The bolt should not be completely removed because
of the possibility of cross threading during re-
installation. Cross threading could result in the loss of a
structural fastener by stripped threads on the nut plate
or by the threads locking and twisting.
REINFECTING SEALANT.If the leak is at the
perimeter of the tank, reinject the sealant. You should
use integral fuel tank groove injector compound and fill
the groove sealant injector gun.
NOTE: Be sure that the gun is filled in such a
manner that no air is trapped in the sealant.
Provide air pressure at the inlet of the gun
according to the gun manufacturers instruc-
The ability of the sealant compound to seal
depends upon its adhesion to metal. Oils and
greases are adhesion breakers and MUST be
completely removed from all sealing areas,
injection tools, and your hands when
operating or servicing the injection gun.
Some common contaminants are hair oils,
body oils, and protective hand creams.
Remove the screws from the injection holes of the
area to be sealed, and place the sealant gun nozzle tip
into the countersink of the injection hole. See figure
3-35. Special fittings may be attached between the
gun tip and the barrel for use in areas of limited
accessibility. Hold the gun firmly in position and
depress the trigger until a plug of sealing compound
at least 1 inch in length flows out of the next adjacent
injection screw hole.
It is essential that the groove between
injection holes be filled by injection from one
direction only. If the sealant is forced into
these areas from two directions, it is possible
that air bubbles will be trapped in the groove.
When injection has been inadvertently made
from two directions, sealant should be
injected from one side until a plug of sealant
5 inches long has been extruded.