Elevator balance tab failure, Boeing 737-229, VH-OZX, Port Moresby, Papua New Guinea, on 31 December 2007

After departing Port Moresby, Papua New Guinea, at 0406 Universal time, coordinated on 31 December 2007, the flight crew of a Boeing 737-229 aircraft, registered VH-OZX, operating a scheduled flight from Port Moresby to Brisbane, experienced severe vibration through the aircraft's airframe, resulting in the crew declaring a MAYDAY and returning to Port Moresby.

A subsequent examination found a section of the right elevator balance tab had detached and was missing. Examination of the remaining sections of the balance tab revealed that two attachment screws from one of the elevator balance tab hinge blocks had unwound, which led to the tab failure.

The investigation found that airframe vibration had been reported by the flight crew the day prior to the accident. On that occasion, a level I - General Inspection of the aircraft was conducted by a licensed aircraft maintenance engineer after the aircraft landed, with no defects found.

The aircraft manufacturer was aware that other operators had experienced in-flight vibration as a result of excessive wear in the elevator balance tab hinge and control linkages, and had issued a number of service bulletins (SBs) to address the issues. These SBs included SB737-55A1070, which directed operators to carry out detailed inspection of the elevator balance tabs, including checks for free-play, control rod wear and loose hinge screws.

As a result of this accident, the aircraft operator implemented a 'fleet campaign directive' requiring the immediate accomplishment of SB 737-55A1070 on all of its aircraft.