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 | 4. Metal Repair Procedures | 4-54. Heat Treatment of Aluminum Alloy Parts
AC 43.13-1B
9/8/98
(1) The acceptable drill size for rivets
may be found in Metallic Materials and Ele
ments for Flight Vehicle Structure
(MIL-HDBK-5).
(2) Avoid drilling oversized holes or
otherwise decreasing the effective tensile areas
of wing-spar capstrips, wing, fuselage, fin-
longitudinal stringers, or highly-stressed ten
sile members. Make all repairs, or reinforce
ments, to such members in accordance with
factory recommendations or with the specific
approval of an FAA representative.
b. Disassembly Prior to Repairing. If
the parts to be removed are essential to the ri
gidity of the complete structure, support the
structure prior to disassembly in such a manner
as to prevent distortion and permanent damage
to the remainder of the structure. When rivets
are removed, undercut rivet heads by drilling.
Use a drill of the same size as the diameter of
the rivet. Drilling must be exactly centered
and to the base of the head only. After drill
ing, break off the head with a pin punch and
carefully drive out the shank. On thin or un
supported metal skin, support the sheet metal
on the inside with a bucking bar. Removal of
rivet heads with a cold chisel and hammer is
not recommended because skin damage and
distorted rivet holes will probably result. In
spect rivet joints adjacent to damaged structure
for partial failure by removing one or more
rivets to see if holes are elongated or the rivets
have started to shear.
c. Effective Tools. Care must also be
taken whenever screws must be removed to
avoid damage to adjoining structure. When
properly used, impact wrenches can be effec
tive tools for removal of screws; however,
damage to adjoining structure may result from
excessive vertical loads applied through the
screw axis. Excessive loads are usually related
to improperly adjusted impact tools or at
tempting to remove screws that have seized
from corrosion. Remove seized screws by
drilling and use of a screw extractor. Once the
screw has been removed, check for structural
cracks that may appear in the adjoining skin
doubler, or in the nut or anchor plate.
4-53. SELECTION OF ALUMINUM
FOR REPLACEMENT PARTS. All alumi
num replacement sheet metal must be identical
to the original or properly altered skin. If an
other alloy is being considered, refer to the in
formation on the comparative strength proper
ties of aluminum alloys contained in
MIL-HDBK-5.
a. Temper. The choice of temper depends
upon the severity of the subsequent forming
operations. Parts having single curvature and
straight bend lines with a large bend radius
may be advantageously formed from
heat-treated material; while a part, such as a
fuselage frame, would have to be formed from
a soft, annealed sheet, and heat-treated after
forming. Make sure sheet metal parts which
are to be left unpainted are made of clad (alu
minum coated) material. Make sure all sheet
material and finished parts are free from
cracks, scratches, kinks, tool marks, corrosion
pits, and other defects which may be factors in
subsequent failure.
b. Use of Annealed Alloys for Struc
tural Parts. The use of annealed aluminum
alloys for structural repair of an aircraft is not
recommended. An equivalent strength repair
using annealed aluminum will weigh more
than a repair using heat-treated aluminum
alloy.
4-54. HEAT TREATMENT OF ALUMI
NUM ALLOY PARTS. All structural alumi
num alloy parts are to be heat-treated in accor
dance with the heat-treatment instruction is
sued by the manufacturers of the part. In the
case of a specified temper, the sequence of
heat-treating operations set forth in
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