On 29 December 2007, a Boeing Company 737-229 aircraft, registered VH-OBN, was being operated on a scheduled passenger service from Brisbane, Qld to Norfolk Island. At 0352 Coordinated Universal Time, the flight crew conducted a missed approach at Norfolk Island due to poor weather.
During the flap retraction, the flight crew felt a high frequency vibration through the airframe, while observing control yoke deflection to the left. Due to the vibration, the aircraft's autopilot system could not be engaged and controlled flight was manually maintained with difficulty. The flight crew elected to continue to the designated alternate airport at Nouméa, New Caledonia. During that diversion flight, the cabin crew prepared the passengers for a possible ditching.
An engineering inspection determined that the number 4 leading edge slat, inboard main track had failed. An examination of the failed track identified fatigue cracking that originated at the intersection of diverging machining marks at the fracture site. Further inspection of the number 4 slat found corrosion damage on the outboard auxiliary track, with the inboard auxiliary track adjacent to the failed main track having failed in overload at the slat attachment.
The investigation also identified a number of cabin safety issues during the diversion flight, and poor passenger handling after the subsequent landing at Nouméa. As a result of this investigation, the aircraft operator advised the Australian Transport Safety Bureau of the implementation of a number of safety actions, including:
- the revision of flight crew flight planning - alternate fuel load provisions
- the revision of cabin crew equipment and procedures
- a review of company emergency response procedures.
At the time of finalising this report, the original operator's air operator's certificate had been taken over by a different organisation. The new organisation does not use the aircraft type involved in this occurrence. It has, however, reviewed its operations to ensure that hazards identified in this investigation are mitigated appropriately.