FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 2. Fabric Covering | 1. Practices and Precautions | 2-7. Fabric Seams
9/8/98
AC 43.13-1B
appropriate non-bleeding cotton adhesive
coated tape, finishing tape, or strips of fabric,
cut from the fabric being used to cover the air
craft, doped in place.
glass fiber deck cloth instead of fabric, no
sealer or dope should be applied to the ply
wood as it would inhibit penetration of epoxy
resin.
(1) Small holes cut through the fabric to
accommodate flying wires, control cables, and
fittings, must be reinforced with finishing tape
or fabric patches cut from the same fabric used
for the covering.
(2) Areas needing additional chafe pro
tection such as control cables routed firm
against the fabric surface should be protected
with patches cut from cotton duck, leather, or
plastic. These patches may be sewn, doped, or
cemented in place, as appropriate.
(3) Any drag and anti-drag wires in the
wings should be protected from chafing at
cross points.
f. Inter-Rib Bracing. Use a woven fabric
tape of the same quality and width as that used
for the rib lace reinforcing, where so incorpo
rated in the wing design by the original aircraft
manufacturer. When the original routing for
the inter rib bracing is not known, the tape will
be routed diagonally, alternating between the
top and bottom of each rib cap on each succes
sive rib, if a single pair, half way between the
front and rear spars. The number of tape pairs
will duplicate the original aircraft manufac
turer’s installation. Tapes will be routed con
tinuously from the wing butt to the wingtip
bow, with one turn of tape around each inter
mediate rib cap strip. Care should be given to
position the tape so as not to interfere with
control cables, bellcranks or push-pull rods.
g. Preparation of Plywood Surfaces for
Covering. Prior to covering plywood sur
faces, prepare the surface by sanding, cleaning,
and applying sealer and dope. When plywood
surfaces are to be covered with light weight
(1) Sand plywood surfaces as needed to
remove old loose dope or varnish residue to
provide a clean bonding surface. Remove any
oil, grease, or other contamination with a suit
able solvent such as naphtha. Small, rough ar
eas and irregularities in the plywood surface
and around any plywood repairs may be filled
and smoothed with an appropriate commercial
grade wood filler. Filling large warp depres
sions on plywood surfaces with a wood filler
for cosmetic purposes is not acceptable.
(2) After cleaning and sanding all ply
wood surfaces, seal the wood grain with a suit
able solvent resistant two-part epoxy varnish.
After the varnish has thoroughly dried, apply
two brush or spray coats of clear dope, allow
ing sufficient drying time between coats.
2-7. FABRIC SEAMS. Seams parallel to
the line of flight are preferable; however,
spanwise seams are acceptable.
a. Sewn Seams.
(1) Machine-sewn seams should be
double stitched using any of the styles illus
trated in figure 2-1 A, B, C, or D. A machine-
sewn seam used to close an envelope at a
wingtip, wing trailing edge, empennage and
control surface trailing edge, and a fuselage
longeron may be made with a single stitch
when the seam will be positioned over a
structure. (See figure 2-1 E.) The envelope
size should accommodate fittings or other
small protrusions with minimum excess for in
stallation. Thick or protruding leading edge
sewn seams should be avoided on thin airfoils
with a sharp leading edge radius because they
may act as a stall strip.
Par 2-6
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