inspection can be used to detect surface cracks in
fittings and the magnetic particle method used to
detect subsurface cracks in ferrous fittings.
Nondestructive inspection of metals is described in
CLEANUP OF DAMAGE.Along with the
investigation of damage, you should clean all jagged
holes, tears, or damaged material. The cleaned
sections must include all the area in which minute
cracks are present. The affected area must be cut and
rounded to form a smooth regular outline. If a
rectangular- or square-shaped cutout is made, the
radii for the corners should be a minimum of
one-fourth inch, unless otherwise specified. All burrs
should be removed from the edges of the cutout.
All dented plates should be restored to their
original shape if possible. Shallow abrasions or
scratches should be burnished with a burnishing tool
that will compress the projecting metal along the
edges down into the scratch. Burnishing has no
cutting action and removes no metal. When surface
irregularities are smoothed by burnishing, the stress
concentration will be lessened.
NOTE: Deep scratches and abrasions must
be treated as complete breaks.
Classification of Damage
After the extent of damage has been determined,
it should be classified in one of the following
categories: negligible damage, damage repairable by
patching, damage repairable by insertion, or damage
requiring replacement of parts. See figure 13-56.
Before proceeding with the repair of the airframe,
it is necessary that the applicable structural repair
manual be consulted for the procedures and materials
to be used. If the applicable manual is not available,
the General Manual for Structural Repair, NA
01-1A-1, may be used. If any conflict should exist
between the two manuals, the specific manual takes
NEGLIGIBLE DAMAGE.Negligible damage
is that damage or distortion that may be allowed to
exist as is or corrected by some simple procedure,
such as removing dents, stop-drilling cracks,
burnishing scratches or abrasions, without placing a
restriction on the flight status of the aircraft. Before
classifying damage as negligible, make sure the
damage complies with the manufacturers specified
limits of negligible damage.
DAMAGE REPAIRABLE BY PATCHING.
Damage that can be repaired by installing a
reinforcement or patch to bridge the damaged portion
of a part may be classified as a damage repairable by
patching. Reinforcement members are attached to the
undamaged portions of the part to restore full
load-carrying characteristics and airworthiness of the
aircraft. Damage repairable by patching is specified
for each member of the airframe.
DAMAGE REPAIRABLE BY INSERTION.
Damage that is extensive enough to involve a major
portion of a member, but which is not so extensive as
to require replacement, is classified as damage
repairable by insertion.
The repair is made by
inserting a new section and splicing it to the affected
DAMAGE REQUIRING REPLACEMENT.
Damage that cannot be repaired by any practical
means is classified as damage requiring replacement.
Short structural members usually must be replaced
because repair of such members is generally
DAMAGE REPAIR PROCEDURES
Damage repair procedures vary greatly from
aircraft to aircraft and the type of repair that is going
to be performed. Also consult the applicable aircraft
MIMs and the applicable aircraft structural repair
manual before performing any structural repairs.
Selection of Repair Material
The major requirement in making a repair is the
duplication of strength of the original structure. You
should consult the structural repair manual for the
aircraft concerned for the alloy thickness and temper
designation of the repair material to be used. This
manual will also designate the type and spacing of
rivets or fasteners to be used in the repair.
In some instances, substitutions of materials are
allowed. When you are making a substitution of
materials and conflicting information between
manuals exists, the structural repair manual for the
aircraft being repaired should be used.