Cessna 172 Maintenance Manual page 56

REPAIR OF THERMO-FORMED THERMO PLASTIC COMPONENTS
Thermo-formed Thermo Plastic Repair
1.
A. Repair of puncture or holes in thermo-formed plastics can be made by trimming out the damaged
area, removing any paint in the area, and installing an overlapping, beveled, or flush patch of identical
material. Doublers may be installed behind the patch where additional strength is desired. MPK,
or any commercially available solvent that will soften and dissolve the plastic, may be used as the
bonding agent. Dissolving some of the plastic shavings in the solvent will furnish additional working
time. Moderate pressure is recommended for best results. Curing time will vary with the agent used,
but repairs should not be strained until fully cured. Cracks can be repaired by saturating the crack itself
with the solvent, then filling with an epoxy filler or a paste made of the plastic shavings and the solvent.
Again, the crack may be reinforced with a doubler on the back side for additional strength. After
the repair has been made, the area may be sanded smooth and painted. Parts that are extensively
damaged should be replaced instead of repaired.
2. Temporary Repairs
A. Crack Repair
(1) It is permissible to stop drill crack(s) that originate at the edge of a fairing if the crack is less than
2 inches (50 mm) in length.
(a) Stop drill the crack with a Number 30 (0.128 inch diameter) drill bit.
(b) A crack may be stop drilled only once.
NOTE:
(c) Any fairing that has a crack that progresses past a stop drilled hole must be repaired or
replaced.
(d) A fairing that has any of the following conditions must have a repair made as soon as
practical:
1
2
(2) Fairings, with a stop drilled crack that does not extend past the stop drilled hole, may remain in
service until the next 100 hour or equivalent inspection.
CESSNA AIRCRAFT COMPANY
SINGLE ENGINE
STRUCTURAL REPAIR MANUAL
A crack that passes through a fastener hole and does not extend to the edge of
the part, may be stop drilled at both ends of the crack.
A crack that is longer than 2 inches (50 mm).
Cracks in more than 10 percent of the attach fastener locations per fairing.
© Cessna Aircraft Company
51-73-01
Page 801
Jun 1/2005