What happened
On 15 June 2011, a Boeing 737-436, registered as ZS-OTF, was performing a scheduled domestic flight from O.R. Tambo International Aerodrome to Cape Town International Aerodrome. During the takeoff roll on runway 03L, the tread of the number 1 tire separated from the tire body. This failure caused minor damage to the aircraft's structure. Following the takeoff, debris consisting of the tire tread and a wheel-well slave door was left on the runway at Johannesburg.
Upon being notified of the thread separation, the captain elected to proceed to the destination. While emergency services at Cape Town International Aerodrome were placed on alert, the flight continued without further incident, and the landing was completed without an emergency. A subsequent inspection after passenger disembarkation revealed damage to the left-hand landing gear doors and the aircraft flaps in the vicinity of the number 1 wheel.
The investigation
An investigation into the incident examined the mechanical state of the aircraft and the specific failure of the tire. The tire was sent to the manufacturer for detailed analysis. The examination determined that the failure was caused by a breakdown in adhesion between the repair rubber and the casing cord structure within the 5-ply casing repair plug. This degradation had likely been developing over several previous landings.
Investigators also looked into the operational environment. The investigation noted that the aircraft was operating under high-performance requirements at a high-elevation airport. The centrifugal forces generated during the takeoff run, combined with the weight of the unworn tread, were sufficient to pull the material away from the casing.
Findings
- The primary cause of the incident was the mechanical breakdown of adhesion within the repair plug of the number 1 tire.
- The failure was exacerbated by the aircraft's use of maximum performance during takeoff at a high-altitude airport.
- The aircraft and its maintenance records were found to be in compliance with all regulatory requirements.
- Weather conditions at the time of the incident were clear and did not contribute to the failure.