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
AC 43.13-1B
9/8/98
(2) Hand sew, with plain overthrow or
baseball stitches at a minimum of four stitches
per inch, or permanent tacking, to the point
where uncut fabric or a machine-sewn seam is
reached. Lock hand sewing at a maximum
of 10 stitch intervals with a double half hitch,
and tie off the end stitch with a double half
hitch. At the point where the hand-sewing or
permanent tacking is necessary, cut the fabric
so that it can be doubled under a minimum of
3/8 inch before sewing or permanent tacking is
performed. (See figure 2-2.)
(3) After hand sewing is complete, any
temporary tacks used to secure the fabric over
wood structures may be removed.
(4) Cover a sewn spanwise seam on a
wing’s leading edge with a minimum 4-inch
wide pinked-edged surface tape with the tape
centered on the seam.
(5) Cover a spanwise-sewn seam at the
wing trailing edge with pinked-edge surface
tape that is at least 3 inches wide. For aircraft
with never-exceed speeds in excess of
200 mph, cut V notches at least 1 inch in depth
and 1/4 inch in width in both edges of the sur
face tape when used to cover spanwise seams
on trailing edges of control surfaces. Space
notches at intervals not exceeding 6 inches.
On tape less than 3 inches wide, the notches
should be 1/3 the tape width. In the event the
surface tape begins to separate because of poor
adhesion or other causes, the tape will tear at a
notched section, thus preventing progressive
loosening of the entire length of the tape which
could seriously affect the controllability of the
aircraft. A loose tape acts as a trim tab only on
a movable surface. It becomes a spoiler on a
fixed surface and has no effect at the trailing
edge other than drag.
(6) Make spanwise-sewn seams on the
wing’s upper or lower surfaces in a manner
that will minimize any protrusions. Cover the
seams with finishing tape at least 3 inches
wide, centering the tape on the seam.
(7) Sewn seams parallel to the line of
flight (chordwise) may be located over ribs.
However, careful attention must be given to
avoid damage to the seam threads by rib lace
needles, screws, rivets, or wire clips that are
used to attach the fabric to the rib. Cover
chordwise seams with a finishing tape at least
3 inches wide with the tape centered on the
seam.
b. Doped Seams.
(1) For an overlapped and doped span-
wise seam on a wing’s leading edge, overlap
the fabric at least 4 inches and cover with fin
ishing tape at least 4 inches wide, with the tape
centered at the outside edge of the overlap
seam.
(2) For an overlapped and doped span-
wise seam at the trailing edge, lap the fabric at
least 3 inches and cover with pinked-edge sur
face tape at least 4 inches wide, with the tape
centered on the outside edge of the overlap
seam.
(3) For an overlapped and doped seam
on wingtips, wing butts, perimeters of wing
control surfaces, perimeters of empennage sur
faces, and all fuselage areas, overlap the fabric
2 inches and cover with a finishing tape that is
at least 3 inches wide, centered on the outside
edge of the overlap seam.
(4) For an overlapped and doped seam
on a wing’s leading edge, on aircraft with a
velocity never exceed (Vne) speed up to and
including 150 mph, overlap the fabric 2 inches
and cover with a finishing tape that is at least
3 inches wide, with the tape centered on the
outside edge of the overlap seam.
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