What happened
On 31 May 2010, a Boeing 747-400SF, registration B-HKH, arrived at London Heathrow Airport from Delhi on a commercial cargo flight. Following landing, the crew noted that the wing flaps were slow to retract, and a 'flap control' status message was recorded in the technical log. During taxiing, the crew identified visible damage to the panels surrounding the inboard flaps on the right wing. Subsequent inspection revealed that the outboard end fitting of the right wing landing gear support beam had failed.
The investigation
The investigation established that the failure of the outboard end fitting allowed the wing landing gear support beam to move slightly within its gate fitting. This movement caused the inboard flap track to misalign, resulting in the right wing flaps contacting and damaging adjacent fairing panels and hydraulic pipes.
Examination of the failed components showed that the fittings on the right wing had developed cracks originating from corrosion pits within the main bore. Laboratory analysis confirmed that the parts were manufactured to specification, but the large bushing lacked the plating required by newer standards. It was determined that the bushing had rotated within the fitting, which dislodged the sealant and permitted moisture to enter the joint.
Findings
- The outboard end fitting of the right wing landing gear support beam failed due to cracks propagating from corrosion pits.
- The rotation of the main bushing caused the failure of the sealant, leading to moisture ingress and subsequent corrosion.
- The movement of the failed fitting caused the misalignment of the right inboard flaps and damage to surrounding wing panels and hydraulic lines.
- The aircraft's fittings were not plated with the protection required by more recent manufacturer standards, a discrepancy potentially due to the age of the components.
- The last detailed inspection of these fittings had been conducted in February 2009, which found them to be in satisfactory condition.