What happened
On 14 June 2008, a Windlass Trike microlight, registration ZU-BCA, departed Ballito Microlight Aerodrome for an introductory flight. The aircraft, carrying a pilot and one passenger, climbed to 1,000 feet before beginning a descent toward Salt Rock beach. While maneuvering between 700 and 800 feet, the aircraft experienced a sudden, sharp jerk as the leading edge of the right wing collapsed. This triggered a transition from a slow spin into a rapid, flat spin, causing the aircraft to impact the sea approximately fifty feet from the shoreline.
Despite the impact, the occupants survived. Nearby swimmers witnessed the accident and immediately assisted in rescuing the pilot and passenger from the water. Both individuals sustained serious injuries, specifically to their lower backs, but were able to be transported to a hospital for surgery. The aircraft was destroyed in the crash.
The investigation
SACAA AIID investigators examined the wreckage and the structural components of the wing. Metallurgical analysis of the fractured right-hand leading edge revealed that the failure occurred at the spreader bar attachment point. Using scanning electron microscopy, investigators identified evidence of inter-sleeve, crevice-type corrosion within the reinforced tubing.
Because the wing's leading edge is constructed of multiple tubes nested within one another, the investigation established that internal corrosion was not visible during standard pre-flight inspections. The aircraft had been operating in the Ballito area, an environment characterized by high humidity and salt air, which is highly corrosive to metal structures.
Findings
- The primary cause of the accident was the failure of the right wing at the spreader bar attachment point.
- This failure was driven by excessive corrosion or potential pre-existing overload damage within the main tubing of the right wing.
- The corrosive nature of the coastal environment, combined with high humidity, significantly degraded the aircraft's metal structure.
- The specific design of the leading edge tubing allowed corrosion to progress undetected inside the sleeves.
Safety action
Following the investigation, several recommendations were noted to mitigate similar risks:
- Implementation of a comprehensive corrosion inspection schedule, developed with the manufacturer, focusing on areas prone to hidden decay.
- Research into the application of corrosion-inhibiting compounds (CICs) in crevices and vulnerable joints.
- The establishment of a database by SACAA to monitor trends in microlight accidents related to corrosion in South Africa.
- The adoption of detailed corrosion control programs by flight schools operating in coastal environments.