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.