What happened
On 20 October 2008, a Boeing Company Mc Donnell Douglas DC9-82, registered PK-LMS, was operating a scheduled passenger flight from Jakarta Soekarno–Hatta Airport to Juanda Airport, Surabaya. The flight was being operated by PT. Wings Abadi Airlines with 174 people on board, including 167 passengers and 7 crew members.
During the landing phase at Surabaya, the aircraft's left inboard main landing gear wheel detached from the axle as the plane touched down. The separation was witnessed by the crew of another aircraft holding at a runway intersection. Following the incident, the flight crew taxied the aircraft to the apron, where a transit check revealed the missing wheel. The detached component was later located on the runway shoulder.
There were no injuries to the passengers or crew, and all occupants disembarked the aircraft normally.
The investigation
Investigators examined the landing gear assembly and the condition of the axle components. Testing revealed that the axle nut and axle cover had separated from the axle, though the locking mechanism remained in its original position.
Technical examinations of the hardware showed that when the detached nut was reinstalled on the affected axle, it remained loose after several turns. Further tests demonstrated that the inner threads of the number-two axle were excessively worn, preventing the nut from being secured with sufficient torque. The investigation also noted that the cockpit voice recorder data was unavailable because the aircraft's power source had not been deactivated following the incident, allowing the recording to be overwritten.
Findings
- The primary cause of the wheel separation was the worn inner threads on the left inboard main landing gear axle.
- The thread joint lacked sufficient strength and tightness to be secured by standard tightening torque.
- The axle was unserviceable at the time of the last wheel replacement, meaning the component should have been replaced rather than reused.
Safety action
Following the investigation, the NTSC issued several recommendations:
- PT. Wings Abadi Airlines was advised to conduct a fleet-wide inspection of landing gear axle threads on its McDonnell Douglas DC9-82 aircraft. The airline subsequently reported that no other worn axles were found in its fleet.
- The airline and the Directorate General of Civil Aviation were advised to implement procedures requiring flight and maintenance crews to deactivate flight recorder power sources immediately following any serious incident to prevent data loss.