TM 55-1520-228-BD
AIRFRAME
d.
Determine the priority of the
various required repairs based on repair
time, difficulty of repair, resources
available, tactical situation, and need
for the aircraft, etc. The longest
repair time normally is given the
highest priority and is most critical.
4-13. ALLOWABLE DAMAGE LIMITS. Damage
limits are calculated on the basis of
the OH-58 structural analysis and tend
to be conservative. Assessors using
damage limits to prepare damage
assessments should consider them as
guides and balance the damage limits
against the judgment resulting from
their own experience.
a. Damage limits are tabulated in
Tables 4-2 thru 4-7 for most primary
structure.
If a damaged member is not
covered in this manual and the damage
appears to exceed authorized limits,
classify the member as unserviceable.
b.
A component that shows signs of
severe overstress such as twisting or
buckling or heat damage should be
treated as failed.
c.
A component should be repaired if
the failed component can overstress
other systems.
d.
Evaluation of Damage to Caps,
Longerons, and Stringers.
Classify
caps,longerons, and stringers as failed
if any of-the following conditions
exist:
(1) Damage exceeds limits
tabulated in Tables 4-2 thru 4-7.
(2) There is damage in four or
more locations within a length of three
feet.
(3) Fasteners securing the com-
ponent to other major components are
sheared, pulled-through, or missing at
one or more locations.
(4) Three or more fasteners next
to each other, which join a cap,
longeron, and stringer to the web, are
sheared, pulled-through or missing.
(5) Twenty percent or more of the
component to web fasteners are similarly
damaged.
(6) Angles and clips securing the
component to another structure are
severely damaged or failed.
e. Evaluation of Damage to Machined
Fittings. Classify a fitting as failed
if any of the following conditions exist:
(1) Damage to the fitting exceeds
the limits contained in Tables 4-2
thru 4-7, or if damage is not tabulated
and exceeds 20 percent of the structural
section in any one location.
(2) One or more fasteners con-
necting the fitting to a structure or to
an aircraft component are bent, sheared,
stripped, or loose.
f.
Evaluation of Splices, Straps,
Doublers, and Gussets. Damage to a
splice, strap, doubler, and gusset will
be evaluated as part of the elements to
which it attaches. Classify a splice,
strap, doubler, or gusset as failed if
any of the following conditions exist:
(1) Damage exceeds the limits con-
tained in Tables 4-2 thru 4-7, or if
damage is not tabulated and exceeds 20
percent of the structural section in
any location.
(2) The part has significant
damage at the intersection of the two
members it connects.
(3) Fasteners securing the part to
a structural member(s) are sheared,
pulled-through, or missing at two or
more adjoining locations.
(4) More than 20 percent of the
total number of fasteners are similarly
damaged.
4-29
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