AC43.13 Chapter 2 Paragraph 2-33 and 2-34.
2-33. STRENGTH CRITERIA FOR
AIRCRAFT FABRIC. Minimum performance standards for new intermediate-grade fabric are specified in TSO-C14b, which references 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 annual inspection, because the strength of the
fabric is a definite factor in the airworthiness
of an airplane. Fabric is considered to be airworthy until it deteriorates to a breaking
strength less than 70 percent of the strength of
new fabric required for the aircraft. For example, 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 fabric) 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 unairworthy when the breaking strength has deteriorated below 56 lb. per inch width.
c. Fabric installed on a glider or sailplane 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 devices used to test fabric by pressing against or
piercing the finished fabric are not FAA approved and are used at the discretion of the
mechanic to base an opinion on the general
fabric condition. Punch test accuracy will depend 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 coatings 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 adding 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
http://rgl.faa.gov/Regulatory_and_G...lar.nsf/list/AC 43.13-1B/$FILE/Chapter 02.pdf