Corrosion Found During Scheduled Inspection
During a C-check on a Boeing 777, an AME discovers extensive corrosion on the wing spar web, adjacent to the fuel tank access panel. The corrosion is beyond the allowable limits in the structural repair manual (SRM). The aircraft is 12 years old and operates in Bahrain's humid and salty environment. The operator is concerned about the cost and downtime. The AME must decide whether to repair or replace the affected structure. The SRM provides a repair scheme that involves blending out the corrosion and installing a reinforcement doubler. However, the doubler requires special rivets that are not in stock and will take 5 days to procure. Alternatively, a replacement spar section is available from another aircraft but requires extensive disassembly and is more costly. The AME seeks guidance from the design organization.
1. Evaluate the options for addressing the corrosion and determine the most appropriate course of action, considering airworthiness and operational constraints.
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The corrosion is beyond allowable limits, so the aircraft is unairworthy until repaired. The two options are: (1) blend out corrosion and install a reinforcement doubler per SRM, requiring 5 days for rivets; (2) replace the spar section with a serviceable part, which is more costly and time-consuming. The AME must prioritize airworthiness and regulatory compliance. The SRM repair is approved and, if properly executed, restores structural integrity. The 5-day wait is acceptable if the operator can tolerate downtime. However, the AME should verify that the corrosion does not exceed the blend-out limits; if it does, the doubler may not be sufficient. The design organization should be consulted to confirm the repair scheme's applicability. The replacement option may be better if the corrosion is widespread or if the doubler repair is not feasible. The AME should also consider the environment: corrosion may recur, so preventive measures (e.g., improved sealants, corrosion inhibiting compounds) should be applied. The decision should be documented, and the CAA may need to be notified if it's a major repair. Ultimately, the AME should choose the option that ensures continued airworthiness and complies with the SRM, while minimizing downtime if possible. The 5-day wait is reasonable if the operator can schedule accordingly.
2. What documentation and certification steps are required before the aircraft returns to service?
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The AME must ensure that the repair is performed in accordance with the SRM or an approved design change. If the SRM repair is used, it is typically a minor repair, but if it involves a doubler, it may be major and require a Form 1 or equivalent. The AME should complete a maintenance record entry detailing the corrosion found, the repair method, and references to the SRM. A certificate of release to service (CRS) must be issued by a licensed AME after verifying that the work was done correctly, including torque values and inspections. If the repair is major, it may require approval from the CAA or a design organization. Additionally, the AME should ensure that any replacement parts have appropriate traceability and certification. Finally, the aircraft's mass and balance may be affected if a doubler is installed, so a weight and balance update may be needed. The AME should also consider repetitive inspections to monitor for recurrence.