What happened
On 7 January 2007, a Boeing 737-300 operated by Metro Batavia Airline, registration PK-YTU, was preparing for departure from Depati Amir Airport in Pangkal Pinang. The flight, 7P524, was scheduled to transport 142 passengers and 6 crew members to Jakarta.
While the aircraft was performing a 180-degree turn to line up on the runway, the pilot heard a noise that sounded like braking components malfunctioning. The crew immediately decided to abort the departure and return to the apron for a technical inspection. Upon examination, the crew discovered that the right nose wheel had detached from the aircraft and was found on the runway shoulder, approximately 3 meters from the pavement. The inspection also revealed that the right nose wheel axle shaft had broken.
The investigation
The investigation focused on the structural integrity of the nose landing gear and recent maintenance activities. Metallurgical analysis conducted by the Institute of Technology, Bandung (ITB) examined the fractured axle shaft. The laboratory findings identified beach marks on the lower portion of the shaft, which provided evidence of a fatigue crack.
Investigators also reviewed maintenance records and practices. It was discovered that a previous replacement of the axle had been performed using an Aircraft Maintenance Manual (AMM) that was not applicable to this specific aircraft model. Additionally, while a torque meter was available, it lacked valid calibration, and the engineer had proceeded with the installation of the torque link without using a meter, assuming specific torque values were unnecessary for the bolts and split pins.
Findings
- The primary cause of the failure was overloaded forces that initiated a crack in the right nose wheel axle shaft.
- Metallurgical evidence indicated that the fatigue crack had been progressing for approximately ten landings prior to the separation event.
- Maintenance procedures were compromised by the use of an incorrect maintenance manual for the specific aircraft type.
- Inadequate use of calibrated tools during the installation of the torque link may have contributed to improper assembly, potentially leading to excessive stiffness or vibration.