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Factual Information

Summary

Following flap retraction shortly after the Boeing 747 departed Sydney, the crew reported a flap disagreement indication. The flaps could not be extended and were stuck in the up position. The aircraft returned to Sydney where the crew carried out a flapless landing.

An inspection revealed that the right inboard fore-flap carriage stop had failed. This resulted in extensive damage to the fore flap, mid flap, and overload failure of the right flap drive torque tubes.

Specialist examination found that the fore-flap carriage stop failed due to stress corrosion cracking. The cracking initiated at the bolt hole surface. The manufacturer's instructions require that the bolt should be installed with wet sealant, however inspection indicated that the sealant did not cover the centre portion of the bolt, potentially allowing moisture to enter.

 
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