becomes brittle around the damaged area as a result of
the heat, and minute cracks are created by the impact
of the projectile. These cracks open up under
vibration. If the projectile passes through the
component or structure, it will leave a larger hole on
the opposite side from where it entered. The repair
procedures for combat damage should be followed
with extreme care only after a rigid inspection of the
damage has been completed in accordance with the
General Manual for Aircraft Battle Damage Repair,
NAVAIR 01-1A-39.
HEAT.—Certain areas of high-performance air-
craft are exposed to high temperatures. These areas
usually include the engine bleed lines, fuselage
sections around the engine, the aft fuselage and
horizontal stabilizer, and the wing sections around the
boundary layer control system. Some aircraft
structural repair manuals include diagrams that
illustrate the heat danger areas.
STRESS.—This type of damage is usually identi-
fied by loosened, sheared, or popped rivets; wrinkled
skin or webs; and cracked or deformed structural
members. This damage is usually caused by violent
maneuvers or hard landings. When the pilot reports
these discrepancies on the yellow sheet, a thorough
inspection of the entire aircraft must be performed.
Investigation of Damage
There are three methods that can be used to
ensure a thorough investigation has been made. The
three methods are visual inspection, hardness testing,
and nondestructive inspection for cracks.
VISUAL INSPECTION.—A thorough inspec-
tion of the structure should be made for dents,
scratches, abrasions, punctures, cracks, distortion,
loose joints, breaks, and buckled or wrinkled skin.
All riveted and bolted joints in the vicinity of the
damaged area should be checked for elongated holes
and loose, sheared, or damaged rivets or bolts. If any
doubt exists about the failure of a rivet or bolt, the
fastener should be removed for a more thorough
inspection. All access panels, hatches, and doors
should be opened to inspect the internal structure.
A borescope (precision optical instrument) can be
used for the inspection of the internal structure. By
using this instrument, areas may be examined without
being disassembled. You can view the area through
the eyepiece.
The adjacent structure should be inspected to
determine if secondary damage has resulted from the
transmission of shock or the load that caused the
primary damage. A shock at one end of a structural
member may be transmitted to the opposite end of the
member and cause rivets to shear or other damage.
When you estimate the extent of damage, be sure that
no secondary damage remains unnoticed.
Every precaution must be taken during the
inspection to ensure that all corrosion is detected,
especially in places where it will not be visible after
repair. Past experience has proven that corrosion
occurs more often in parts of the structure that are
poorly ventilated and in inaccessible corners of
internal joints that prevent proper water drainage.
HARDNESS TESTING.—When fire has
damaged the airframe, the paint will be blistered or
scorched and the metal will be discolored. When
these conditions exist, the affected area should first be
cleaned and the paint removed. Following this, a
hardness test should be conducted to determine if the
metal has lost any of its strength characteristics. This
test can be performed with the Barcol or Riehle
portable hardness tester (described in chapter 1 of this
manual). If the material to be tested is removed from
the airframe, then a more reliable test can be made by
using a standard bench tester (also described in
chapter 1). If the alloy to be tested is either clad or
anodized, the surface coating must be removed to the
bare metal at the point of penetrator contact. This is
necessary because clad surfaces are softer and
anodized surfaces are harder than the base alloy.
INSPECTION FOR CRACKS.—The existence
of suspected cracks or the full extent of apparent
cracks in structural members cannot be accurately
determined by visual inspection. In cases where it is
necessary for cracks to be accurately defined, a
nondestructive inspection is usually performed.
Fittings should receive a special investigation if
they are cracked, since this could cause an entire
component to fail. Fittings are used to attach sections
of wings together and wings to fuselage, as well as
attachment of stabilizers, control surfaces, landing
gear, and engine mounts. The penetrant method of
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