AIRCRAFT NONMETALLIC REPAIR
otherwise damaging the plastic surface. The following
general rules apply:
This chapter deals with the materials and pro-
1. Transparent plastic materials should be han-
cedures to be used in the repair of nonmetallic and
dled only with clean cotton gloves.
advanced composite materials used in aircraft
construction. The procedures discussed are general in
2. The use of harmful liquids, such as cleaning
nature. When actually repairing nonmetallic or
agents, should be avoided.
advanced composite materials, you should refer to the
3. Fabrication, repair, installation, and mainte-
applicable maintenance instruction manual (MIM) and
nance instructions must be closely followed.
structural repair manual (SRM).
4. Operations that might tend to scratch or distort
the plastic surface must be avoided. You must take care
MAINTAINING AND REPAIRING
to avoid scratching plastic surfaces with finger rings or
other sharp objects.
Just as woods split and metals crack in areas of
LEARNING OBJECTIVE: Recognize the
high, localized stress, plastic materials develop, under
procedures for cleaning, repairing, or replacing
similar conditions, small surface fissures called
aircraft nonmetallic structures and surfaces.
crazing. These tiny cracks are approximately perpen-
This chapter covers some of the procedures used in
dicular to the surface, very narrow in width, and usually
the repair or replacement of aircraft nonmetallic
not over 0.01 inch in depth. These tiny fissures are not
structures. Because no one set of rules applies to all
only an optical defect, but also a mechanical defect, as
aircraft, you should refer to the maintenance instruction
there is a separation or parting of material.
manual (MIM) and structural repair manual (SRM) for
If the crazing is in a random pattern, it is usually
the materials and procedures for a particular aircraft.
caused by the action of solvent or solvent vapors. If the
MAINTAINING TRANSPARENT PLASTIC
crazing is approximately parallel, it is usually caused
by directional stress, set up by cold forming, excessive
loading, improper installation, improper machining, or
Because of the many uses of plastic materials in
a combination of these with the action of solvents or
aircraft, optical quality is of great importance. These
plastic materials are similar to plate glass in many of
Crazing can be caused by improper cleaning,
their optical characteristics. Ability to locate and
improper installation, improper machining, or cold
identify other aircraft in flight, to land safely at high
forming. Once a part has been crazed, neither the
speeds, to maintain position in formation, and in some
optical nor the mechanical defect can be removed
cases, to sight guns accurately through plastic
permanently; therefore, prevention of crazing is very
enclosures all depend upon the surface cleanliness,
clarity, and freedom from distortion of the plastic
material. These factors depend entirely upon the
Cleaning Plastic Surfaces
amount of care exercised in the handling, fabrication,
maintenance, and repair of the material.
Masking paper should be left on the plastic as long
as possible. When it is necessary to remove the masking
Plastics have many advantages over glass for
paper from the plastic during fabrication or installation,
aircraft application, particularly the lightness in weight
the surface should be remasked as soon as possible.
and ease of fabrication and repairs. They lack the
Either replace the original paper or apply masking tape.
surface hardness of glass and are very easily scratched,
If the masking paper adhesive deteriorates, making
with resulting impairment of vision. You must exercise
removal of paper difficult, moisten the paper with
care while servicing all aircraft to avoid scratching or