AIRCRAFT NONMETALLIC REPAIR
Chapter Objective: Upon completion of this chapter, you will have a working
knowledge of the basic repair techniques associated with aircraft nonmetallic
You will also have a working knowledge of advanced composite
materials, their unique characteristics, and special techniques and safety
procedures associated with composite repair materials.
This chapter deals with the materials and
procedures to be used in the repair of nonmetallic and
advanced composite materials used in aircraft
construction. The procedures discussed are general in
nature. When actually repairing nonmetallic or
advanced composite materials, you should refer to the
applicable maintenance instruction manual (MIM)
and structural repair manual (SRM).
MAINTAINING AND REPAIRING
Recognize the proce-
dures for cleaning and repairing or
replacement of aircraft nonmetallic
structures and surfaces.
In the following text, we will discuss some of the
procedures used in the repair or replacement of
aircraft nonmetallic structures. Because no one set of
rules applies to all aircraft, you should refer to the
maintenance instruction manual (MIM) and structural
repair manual (SRM) for the materials and procedures
for a particular aircraft.
MAINTAINING TRANSPARENT PLASTIC
Because of the many uses of plastic materials in
aircraft, optical quality is of great importance. These
plastic materials are similar to plate glass in many of
their optical characteristics. Ability to locate and
identify other aircraft in flight, to land safely at high
speeds, to maintain position in formation, and in some
cases, to sight guns accurately through plastic
enclosures all depend upon the surface cleanliness,
clarity, and freedom from distortion of the plastic
These factors depend entirely upon the
amount of care exercised in the handling, fabrication,
maintenance, and repair of the material.
Plastics have many advantages over glass for
aircraft application, particularly the lightness in
weight and ease of fabrication and repairs. They lack
the surface hardness of glass and are very easily
scratched, with resulting impairment of vision. You
must exercise care while servicing all aircraft to avoid
scratching or otherwise damaging the plastic surface.
Specific procedures are described later in this
section for minor maintenance; however, the
following general rules are emphasized:
1. Transparent plastic materials should be
handled only with clean cotton gloves.
2. The use of harmful liquids, such as cleaning
agents, should be avoided.
3. Fabrication, repair, installation, and mainte-
nance instructions must be closely followed.
4. Operations that might tend to scratch or distort
the plastic surface must be avoided. You must take
care to avoid scratching plastic surfaces with finger
rings or other sharp objects.
Just as woods split and metals crack in areas of
high, localized stress, plastic materials develop, under
similar conditions, small surface fissures called
These tiny cracks are approximately
perpendicular to the surface, very narrow in width,
and usually not over 0.01 inch in depth. These tiny
fissures are not only an optical defect, but also a
mechanical defect, as there is a separation or parting
If the crazing is in a random pattern, it is usually
caused by the action of solvent or solvent vapors. If
the crazing is approximately parallel, it is usually
caused by directional stress, set up by cold forming,
excessive loading, improper installation, improper