FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 2. Fabric Covering | 3. Inspection and Testing | 2-34. Fabric Testing
9/8/98
AC 43.13-1B
a. If the fabric type is determined to be
polyester, coating identification should start
by reviewing the aircraft records and inspect-
ing the inside of the wings and the fuselage for
the required fabric source identification stamps
for covering materials authorized under the
STC. The manual, furnished by the holder of
the STC-approved fabric, should be reviewed
to determine whether the coatings are those
specified by the STC.
b. Coating types, other than those
authorized by the original STC, may have been
used with prior FAA approval, and this would
be noted in the aircraft records. The presence
of dope on polyester can be detected by a sam-
ple burn test.
2-33. STRENGTH CRITERIA FOR
AIRCRAFT FABRIC. Minimum perform-
ance standards for new intermediate-grade fab-
ric are specified in TSO-C14b, which refer-
ences AMS 3804C. Minimum performance
standards for new Grade A fabric are specified
in TSO-C15d, which references AMS 3806D.
a. The condition of the fabric covering
must be determined on every 100-hour and an-
nual inspection, because the strength of the
fabric is a definite factor in the airworthiness
of an airplane. Fabric is considered to be air-
worthy until it deteriorates to a breaking
strength less than 70 percent of the strength of
new fabric required for the aircraft. For exam-
ple, if grade-A cotton is used on an airplane
that requires only intermediate fabric, it can
deteriorate to 46 pounds per inch width
(70 percent of the strength of intermediate fab-
ric) before it must be replaced.
b. Fabric installed on aircraft with a
wing loading less than 9 lb. per square foot
(psf), and a Vne less than 160 mph, will be
considered unairworthy when the breaking
strength has deteriorated below 46 lb. per inch
width, regardless of the fabric grade. Fabric
installed on aircraft with a wing loading of
9 lb. per square foot and over, or a Vne of
160 mph and over, will be considered unair-
worthy when the breaking strength has deterio-
rated below 56 lb. per inch width.
c. Fabric installed on a glider or sail-
plane with a wing loading of 8 lb. per square
foot and less, and a Vne of 135 mph or less,
will be considered unairworthy when the fabric
breaking strength has deteriorated below 35 lb.
per inch width, regardless of the fabric grade.
2-34. FABRIC TESTING. Mechanical de-
vices used to test fabric by pressing against or
piercing the finished fabric are not FAA ap-
proved and are used at the discretion of the
mechanic to base an opinion on the general
fabric condition. Punch test accuracy will de-
pend on the individual device calibration, total
coating thickness, brittleness, and types of
coatings and fabric. Mechanical devices are
not applicable to glass fiber fabric that will
easily shear and indicate a very low reading
regardless of the true breaking strength. If the
fabric tests in the lower breaking strength
range with the mechanical punch tester or if
the overall fabric cover conditions are poor,
then more accurate field tests may be made.
Cut a 1-1/4-inch wide by 4-inch long sample
from a top exposed surface, remove all coat-
ings and ravel the edges to a 1-inch width.
Clamp each end between suitable clamps with
one clamp anchored to a support structure
while a load is applied (see table 2-1) by add-
ing sand in a suitable container suspended a
few inches above the floor. If the breaking
strength is still in question, a sample should be
sent to a qualified testing laboratory and
breaking strength tests made in accordance
with American Society of Testing Materials
(ASTM) publication D5035.
Par 2-32
Page 2-35