Cessna 172 Maintenance Manual page 124

1. Damage Classification
A. Damage to the wing and its component assemblies can be divided into three major categories:
negligible damage, repairable damage, and damage necessitating replacement of parts. These
categories are intended to provide the mechanic with some general guidelines to use in determining
the extent and criticalness of any damage. Obviously, there will be some overlapping between
categories, and common sense should be used in determining the final action to be taken with regard
to any damage.
B. For an illustration of various wing component repairs, refer to applicable sections within this chapter.
2. Wing Skin Damage Criteria
A. Negligible damage: Any smooth dents in the wing skin that are not more than 0.030 inch below
contour and can be circumscribed with a 2 inch diameter circle that have no evidence of skin tears,
cracks, or skin penetrations - which are not stress wrinkles and do not interfere with internal structure
of mechanism - constitute negligible damage; and rework is considered cosmetic.
B. Repairable damage: Dents or dings deeper and/or larger than specified above must be repaired.
Skin tears, cracks or penetrations must be repaired. Dings that include understructure (ribs, frames
and spars) must be repaired by reforming or removal and replacement of the damaged member or
damaged are. Reevaluation of the skin after repair of the understructure will determine if the skin
damage is negligible, repairable or requires replacement.
C. Damage Necessitating Replacement Of Parts: If a skin is badly damaged, repair must be made by
replacing an entire skin panel from one structural member to the next. Repair seams must be made
to lie along structural members and each seam must be made exactly the same in regard to rivet size,
spacing and pattern as the manufactured seams at the edges of the original sheet. If the manufactured
seams are different, the stronger must be copied. If the repair ends at a structural member where
no seam is used, enough repair panel must be used to allow an extra row of staggered rivets, with
sufficient edge margin, to be installed.
3. Wing Stringer Damage Criteria
A. Negligible Damage: Minor Scratches or abrasions are the only form of damage considered negligible
to wing stringers.
B. Repairable damage: Dents or bends in a stringer may be repaired by reforming or by replacing a
section of the stringer. Since aluminum work hardens, it is much more likely to crack when reformed
and should be carefully inspected for such cracks after rework. Removal and replacement of damaged
stringers is preferred to reformation.
C. Damage Necessitating Replacement Of Parts: If a stringer is so badly damaged that more than one
section must be spliced, replacement is recommended.
4. Wing Auxiliary Spar Damage Criteria
A. Negligible damage: Minor scratches or abrasions are the only form of damage considered negligible
to wing auxiliary spars.
B. Repairable damage: Dents or bends in an auxiliary spar may be repaired by reforming or by replacing
a section of the auxiliary spar. Since aluminum work hardens, it is much more likely to crack when
reformed and should be carefully inspected for such cracks after rework. Removal and replacement
of a damaged section to the auxiliary spar is preferred to reformation.
C. Damage necessitating Replacement Of Parts: If damage to an auxiliary spar would require a repair
which could not be made between adjacent ribs, the auxiliary spar must be replaced.
5. Wing Rib Damage Criteria
A. Negligible damage: None, other than minor scratches or abrasions.
CESSNA AIRCRAFT COMPANY
SINGLE ENGINE
STRUCTURAL REPAIR MANUAL
WING DAMAGE CLASSIFICATION
© Cessna Aircraft Company
57-10-00
Page 1
Jun 1/2005