8.0.4 SPECIAL INSPECTION NOTES:
Corrosion
Corrosion in and around a Structural Significant Item (SSI) may alter its damage tolerance characteristics, however, the effects have not been included in crack growth calculations for SSIs in this document. Therefore, it is important that operators have corrosion control inspections integrated into the scheduled maintenance program at frequencies based on experience or as suggested in the Corrosion Prevention and Control Program (CPCP), found in MPD Section 10 (D6-38278). SSID inspection areas in which corrosion has been reported include:
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Lower fuselage structure in the bilge area, where moisture might collect;
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Keel beam webs and chords, particularly the internal surfaces from the wing front spar to the main landing gear wheel well aft bulkhead.
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Lower lobe cargo door cut-out sills.
Findings of significant corrosion in the areas of the SSI not previously reported should be included in the reporting system for the CPCP as described in Section 10 of the MPD.
Indicators of Structural Distress
For specific inspection areas covered in this document and in general airline inspection areas of aging airplanes, certain signs of structural distress should be treated as potentially serious problems with additional evaluation and inspection of the adjacent structure considered. Once the operator gains access to an area, all adjacent structure should be given a thorough visual inspection. If a crack(s) is found during inspection within a designated area, the inspection must be expanded until it is assured that any additional cracks have been located and repaired.
One example of "Distress Indicator" is a wing fuel leak which could result from wing skin cracking. It is recognized that airlines conduct routine area inspections, at specified intervals, which are capable of detecting wing fuel leaks. This type of potential damage indicator is significant and it is recommended that additional detailed visual or NDT inspections be accomplished until the problem is defined and corrective action is taken. Repetitive and excessive use of sealant to prevent fuel leaks at fastener locations should be avoided.
Some additional examples of "Distress Indicators" are:
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Fuselage pressure leaks.
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Distressed fasteners in primary structure - loose, popped, dished, tipped heads.
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