What happened
On 28 September 2021, a Boeing B737-400 cargo aircraft, registration HS-KMC, was performing a scheduled departure from Singapore Changi Airport to Jakarta Soekarno-Hatta Airport. During the take-off roll on Runway 02R, both tyres on the left landing gear suffered a blowout. The failure of the outboard tyre (Wheel #1) was immediately followed by the failure of the inboard tyre (Wheel #2), which also caused a landing gear panel to detach from the aircraft.
Despite the incident, the aircraft successfully lifted off and continued to Indonesia. The flight crew, unaware of the specific nature of the failure, noted only a loud thud during the rotation. Upon landing in Jakarta, the crew observed aircraft vibrations and a slight tilt to the left side while taxiing. Ground personnel subsequently confirmed the tyre blowouts to the crew, and the aircraft was towed to a parking bay.
The investigation
The investigation examined the mechanical failure of the tyres, the maintenance records of the operator, and the communication of debris information between air traffic control centers. Investigators analyzed tyre debris recovered from Changi Airport, which included fragments from both wheels. The inspection also revealed damage to the aircraft's wing skin, landing lights, and a broken flap link caused by the impact of the tyre debris.
Review of maintenance logs revealed that the inboard tyre had been replaced just two days prior due to a leaking air valve. Investigators also scrutinized the operator's daily pressure check records, noting discrepancies and unannotated amendments made by management to inflation figures.
Findings
- The primary cause of the failure was an under-inflation condition in the previously replaced inboard tyre, which led to the overloading and subsequent failure of the outboard tyre.
- Maintenance documentation practices were found to be inadequate, specifically regarding the failure to record precise tyre pressures following replacements and the improper amendment of daily check logs.
- Information regarding the runway debris was not communicated to the flight crew in a timely manner because the AFTN messages sent by Singapore ATC were not classified with an urgent priority indicator.
Safety action
Following the investigation, Singapore ATC implemented several improvements, including the use of a new quick reference checklist for managing foreign object debris (FOD) and a requirement to classify all AFTN messages concerning suspected aircraft parts as urgent. Additionally, safety recommendations were issued to the aircraft operator to review maintenance quality procedures and emphasize the necessity of accurate documentation for wheel-related maintenance.