Cessna 172 Skyhawk SERIES, Maintenance Manual

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CESSNA AIRCRAFT COMPANY
SINGLE ENGINE
STRUCTURAL REPAIR MANUAL
B. Repairable damage: Dents or bends in a rib may be repaired by reforming or by replacing a section
of the rib. 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 rib is preferred to reformation.
C. Damage Necessitating Replacement Of Parts: Leading and trailing edge ribs that are extensively
damaged can be replaced. However, due to the necessity of unfastening an excessive amount of
skin in order to replace the rib, they should be repaired if practical. Center ribs, between the front and
rear spar, should always be repaired if practical.
6. Wing Spar Damage Criteria
A. Negligible damage: Due to the stress which wing spars encounter, very little damage can be
considered negligible. All cracks, stress wrinkles, deep scratches, and sharp dents must be repaired.
Smooth dents, light scratches and abrasions may be considered negligible.
B. Repairable damage: While it is possible to repair the spar channel by reforming a section of the spar,
replacement is preferred. A service kit (SK172-68) is available for replacement of the inboard end of
the rear spar for damage that typically occurs with impact on the outboard leading edge.
C. Damage Necessitating Replacement of Parts: Damage so extensive that repair is not practical
requires replacement of complete wing spar.
7. Wing Fuel Bay Spars/Rib Damage Criteria
A. Negligible damage: Any smooth dents in the wing fuel spar and ribs that have no evidence of tears,
cracks or penetrations - which are not stress wrinkles and do not change (Oil can, or pop in and out)
with internal pressure - are considered negligible damage.
B. Repairable damage: Dents or bends in the wing fuel spar and ribs may be repaired by reforming
or by replacing a section of the structure. 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 is preferred to reformation.
C. Damage Necessitating Replacement Of Parts: Due to the amount of fuel bay sealant which must be
removed from fuel bay components to facilitate repair, individual parts are not available to replace fuel
bay spars or ribs. The entire fuel bay area must be replaced as a unit.
8. Wing Leading Edge Damage Criteria
A. Negligible damage: Any smooth dents in the wing leading edge skin that are not more than 0.030
inch (0.76 mm) below contour and circumscribable with not more than a 1.5 inch (38 mm) diameter
circle that has no evidence of skin tears, cracks, or skin penetrations - which are not stress wrinkles
and do not interfere with internal structure - constitute negligible damage. However, because of the
critical nature of the wing leading edge, this cosmetic repair should be completed.
B. Repairable damage: Dents or dings deeper and/or larger than speci fi ed above must be repaired. Skin
tears, cracks or penetrations must be repaired. Dings that include ribs must be repaired by reforming
or removal and replacement of the rib. Reevaluation of the skin after the repair of the understructure
will determine if the skin damage is negligible, repairable or requires replacement.
C. Damage Necessitating Replacement Of Parts: Where extreme damage has occurred, complete
leading edge skin panels should be replaced.
9. Bonded Leading Edge Damage Criteria
A. Negligible damage: Any smooth dents in the wing leading edge skin that are not more than 0.030
inch (0.76 mm) below contour and circumscribable with not more than a 1.5 inch (38 mm) diameter
circle that has no evidence of skin tears, cracks, or skin penetrations - which are not stress wrinkles
and do not interfere with internal structure - constitute negligible damage. However, because of the
critical nature of the wing leading edge, this cosmetic repair should be completed.
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© Cessna Aircraft Company
Jun 1/2005