FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 4. Metal Structure, Welding, and Brazing | 5. Welding and Brazing | 4-99. Engine Mount Repairs
9/27/01
AC 43.13-1B CHG 1
Spring the long stub of the original tube from
the normal position, slip the replacement tube
over the long stub, and then back over the
short stub. Center the replacement tube be
tween the stubs of the original tube. Tack
weld one end of the replacement tube in sev
eral places, then weld completely around the
end. In order to prevent distortion, allow the
weld to cool completely, then weld the re
maining end of the replacement tube to the
original tube.
4-98. REPAIRS AT BUILT-IN FUSE
LAGE FITTINGS. Make splices in accor
dance with the methods described in para
graphs 4-86 through 4-92. Repair built-in fu
selage fittings in the manner shown in fig
ure 4-41. The following paragraphs outline the
different methods as shown in figure 4-41.
a. Tube of Larger Diameter Than Origi
nal. A tube (sleeve) of larger diameter than
the original is used in the method shown in
figure 4-41 (A). The forward splice is a
30-degree scarf splice. Cut the rear longeron
(right) approximately 4 inches from the cen
terline of the joint and fit a 1 inch long spacer
over the longeron, and edge weld this spacer
and longeron. Make a tapered “V” cut ap
proximately 2 inches long in the aft end of the
outer sleeve, and swage the end of the outer
sleeve to fit the longeron and weld.
b. Tube of Same Diameter as Original. In
the method shown in figure 4-41 (B) the new
section is the same size as the longeron
forward (left) of the fitting. The rear end
(right) of the tube is cut at 30 degrees and
forms the outside sleeve of the scarf splice. A
sleeve is centered over the forward joint as in
dicated.
c. Simple Sleeve. In figure 4-41 (C), it is as
sumed the longeron is the same size on each
side of the fitting. It is repaired by a sleeve of
larger diameter than the longeron.
d. Large Difference in Longeron Diameter
Each Side of Fitting. Figure 4-41 (D) as
sumes that there is 1/4-inch difference in the
diameter of the longeron on the two sides of
the fitting. The section of longeron forward
(left) of the fitting is cut at 30 degrees, and a
section of tubing of the same size as the tube
and of such length as to extend well to the rear
(right) of the fitting is slipped through it. One
end is cut at 30 degrees to fit the 30-degree
scarf at left, and the other end fishmouthed.
This makes it possible to insert a tube of
proper diameter to form an inside sleeve for
the tube on the left of the fitting and an outside
sleeve for the tube on the right of the fitting.
4-99. ENGINE-MOUNT REPAIRS. All
welding on an engine mount must be of the
highest quality, since vibration tends to ac
centuate any minor defect. Engine-mount
members should preferably be repaired by us
ing a larger diameter replacement tube, tele
scoped over the stub of the original member,
and using fishmouth and rosette welds. How
ever, 30-degree scarf welds in place of the
fishmouth welds will be considered acceptable
for engine-mount repair work.
a. Repaired engine mounts must be checked
for accurate alignment. When tubes are used
to replace bent or damaged ones, the original
alignment of the structure must be maintained.
When drawings are not available, this can be
done by measuring the distance between points
of corresponding members that have not been
distorted.
b. Grind out all cracked welds.
c. Use only high-grade metallurgically con
trolled (mc) welding rods for engine-mount re
pairs.
Par 4-97
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