cleaned and the paint removed. Following this, a
STRESS.--This type of damage is usually iden-
hardness test should be conducted to determine if the
tified by loosened, sheared, or popped rivets; wrinkled
metal has lost any of its strength characteristics. This
skin or webs; and cracked or deformed structural
test can be performed with the Barcol or Riehle
members. This damage is usually caused by violent
portable hardness tester. If the material to be tested is
maneuvers or hard landings. When the pilot reports
removed from the airframe, then a more reliable test
these discrepancies on the yellow sheet, a thorough
can be made by using a standard bench tester. If the
inspection of the entire aircraft must be performed.
alloy to be tested is either clad or anodized, the surface
Investigation of Damage
coating must be removed to the bare metal at the point
of penetrator contact. This is necessary because clad
There are three methods that can be used to ensure
surfaces are softer and anodized surfaces are harder
a thorough investigation has been made. The three
than the base alloy.
methods are visual inspection, hardness testing, and
INSPECTION FOR CRACKS.--The existence
nondestructive inspection for cracks.
of suspected cracks or the full extent of apparent cracks
VISUAL INSPECTION.--A thorough inspection
in structural members cannot be accurately determined
of the structure should be made for dents, scratches,
by visual inspection. In cases where it is necessary for
abrasions, punctures, cracks, distortion, loose joints,
cracks to be accurately defined, a nondestructive
breaks, and buckled or wrinkled skin. All riveted and
inspection is usually performed.
bolted joints in the vicinity of the damaged area should
Fittings should receive a special investigation if
be checked for elongated holes and loose, sheared, or
they are cracked, since this could cause an entire
damaged rivets or bolts. If any doubt exists about the
component to fail. Fittings are used to attach sections of
failure of a rivet or bolt, the fastener should be removed
wings together and wings to fuselage, as well as
for a more thorough inspection. All access panels,
attachment of stabilizers, control surfaces, landing
hatches, and doors should be opened to inspect the
gear, and engine mounts. The penetrant method of
internal structure. A borescope (precision optical
inspection can be used to detect surface cracks in
instrument) can be used for the inspection of the
fittings and the magnetic particle method used to detect
internal structure. By using this instrument, areas may
subsurface cracks in ferrous fittings.
be examined without being disassembled. You can
view the area through the eyepiece.
CLEANUP OF DAMAGE.--Along with the
investigation of damage, you should clean all jagged
The adjacent structure should be inspected to
holes, tears, or damaged material. The cleaned sections
determine if secondary damage has resulted from the
must include all the area in which minute cracks are
transmission of shock or the load that caused the
present. The affected area must be cut and rounded to
primary damage. A shock at one end of a structural
form a smooth regular outline. If a rectangular- or
member may be transmitted to the opposite end of the
square-shaped cutout is made, the radii for the corners
member and cause rivets to shear or other damage.
should be a minimum of one-fourth inch, unless
When you estimate the extent of damage, be sure that
otherwise specified. All burrs should be removed from
no secondary damage remains unnoticed.
the edges of the cutout.
Every precaution must be taken during the
All dented plates should be restored to their
inspection to ensure that all corrosion is detected,
original shape if possible. Shallow abrasions or
especially in places where it will not be visible after
scratches should be burnished with a burnishing tool
repair. Past experience has proven that corrosion occurs
that will compress the projecting metal along the edges
more often in parts of the structure that are poorly
down into the scratch. Burnishing has no cutting action
ventilated and in inaccessible corners of internal joints
and removes no metal. When surface irregularities are
that prevent proper water drainage.
smoothed by burnishing, the stress concentration will
HARDNESS TESTING.--When fire has dam-
be lessened.
aged the airframe, the paint will be blistered or
NOTE: Deep scratches and abrasions must be
scorched and the metal will be discolored. When these
treated as complete breaks.
conditions exist, the affected area should first be
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