FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 1. Wood Structure | 1. Materials and Practices | 1-4. Adhesives
AC 43.13-1B CHG 1
9/27/01
(1) Refer to the aircraft maintenance or
repair manual for specific instructions on ac-
ceptable adhesive selection for use on that type
aircraft.
(2) Adhesives meeting the requirements
of a Military Specification (Mil Spec), Aero-
space Material Specification (AMS), or Tech-
nical Standard Order (TSO) for wooden air-
craft structures are satisfactory providing they
are found to be compatible with existing
structural materials in the aircraft and the fab-
rication methods to be used in the repair.
b. Common types of adhesives that are
or have been used in aircraft structure fall into
two general groups: casein and synthetic-
resins. Adhesive technology continues to
evolve, and new types (meeting the require-
ments of paragraph 1-4a) may become avail-
able in the future.
(1) Casein adhesive performance is
generally considered inferior to other products
available today, modern adhesives should be
considered first.
CAUTION: Casein adhesive deterio-
rates over the years after exposure to
moisture in the air and temperature
variations. Some modern adhesives
are incompatible with casein adhesive.
If a joint that has previously been
bonded with casein is to be rebonded
with another type adhesive, all traces
of the casein must be scraped off be-
fore the new adhesive is applied. If
any casein adhesive is left, residual al-
kalinity may cause the new adhesive to
fail to cure properly.
(2) Synthetic-resin adhesives comprise
a broad family which includes plastic resin
glue, resorcinol, hot-pressed Phenol, and ep-
oxy.
(3) Plastic resin glue (urea-formalde-
hyde resin glue) has been used in wood aircraft
for many years. Caution should be used due to
possible rapid deterioration (more rapidly than
wood) of plastic resin glue in hot, moist envi-
ronments and under cyclic swell-shrink stress.
For these reasons, urea-formaldehyde should
be considered obsolete for all repairs. Any
proposed use of this type adhesive should be
discussed with the appropriate FAA office
prior to using on certificated aircraft.
(4) Federal Specification MMM-A-
181D and Military Specification MIL-A-22397
both describe a required series of tests that
verify the chemical and mechanical properties
of resorcinol. Resorcinol is the only known
adhesive recommended and approved for use
in wooden aircraft structure and fully meets
necessary strength and durability requirements.
Resorcinol adhesive (resorcinol-formaldehyde
resin) is a two-part synthetic resin adhesive
consisting of resin and a hardener. The appro-
priate amount of hardener (per manufacturer’s
instruction) is added to the resin, and it is
stirred until it is uniformly mixed; the adhesive
is now ready for immediate use. Quality of fit
and proper clamping pressure are both critical
to the achievement of full joint strength. The
adhesive bond lines must be very thin and uni-
form in order to achieve full joint strength.
CAUTION: Read and observe mate-
rial safety data. Be sure to follow the
manufacturer’s instructions regarding
mixing, open assembly and close as-
sembly times, and usable temperature
ranges.
(5) Phenol-formaldehyde adhesive is
commonly used in the manufacturing of air-
craft grade plywood. This product is cured at
elevated temperature and pressure; therefore, it
is not practical for use in structural repair.
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