Damages are classified as negligible, repairable by patching,
repairable by insertion, and repairable by replacement. Availability
of repair materials and time can influence the decision to repair or
replace a part.
Corrosion is the process of a metal deteriorating by chemical
painting metals subject to corrosion.
Control of this process is
necessary to protect aircraft operational integrity, limit expenses,
and reduce maintenance manhours.
Corrosion classifications are
uniform etch effect, pitting, intergranular, exfoliation, galvanic,
concentration cell, and stress corrosion cracking, and fatigue
Inspections for corrosion must be made at all periodic
The five stresses an aircraft is subject to are tension, compression,
shear, bending, and torsion.
The first three are called basic
stresses and the others are called combination stresses.
torsion, and shear are the most frequently encountered in airframe
The prime requirement in repair material selection is to duplicate
the structure's original strength.
Caution must be used if alloys
must be substituted, and the applicable technical manual must be
New sections for repair or replacement must be made to
the dimensions given in the appropriate technical manual.
addition, material must be marked with an aircraft marking pencil to
prevent harmful scratches being made on the metal.
In general, the rivet size and alloy used in the repair must be the
same as the original. For reworked enlarged or deformed rivet holes
the next size rivet must be used.
If blind rivets are used, the
applicable technical manual must be consulted for type, size, number,
spacing, and edge distance.
STRESSED SKIN REPAIRS
Skin patches are divided into two general types: the lap and flush
A lap patch is externally applied and has its edges
overlapping the skin.
The patch's overlapping portions are riveted
to the skin.
This kind of patch is permitted in certain areas on
some aircraft, but only where aerodynamic smoothness is unimportant.
The flush patch, shown in Figure 2-2, is inserted into the repaired
area and is riveted to a reinforcement plate (doubler) that in turn
is riveted to the inside of the skin.