What happened
On the morning of 9 February 2007, an Agusta 109E helicopter, registration ZS-RJD, departed Rand Aerodrome for a commercial flight to Moroa Mine. The mission involved transporting platinum concentrate for processing. Shortly after liftoff, while at an altitude of approximately 200 feet, the pilot retracted the landing gear.
During the climb, air traffic control notified the pilot that an observer had seen an object fall from the aircraft. The pilot immediately slowed the helicopter and cycled the landing gear; although cockpit indicators showed the gear was locked, the pilot was advised to perform a flypast for visual inspection. A nearby police helicopter joined the aircraft in formation, at which point the crew confirmed that the left main wheel assembly had completely detached.
The pilot returned to Rand Aerodrome, where the passenger disembarked via a low hover. After a preliminary inspection by maintenance personnel, the pilot proceeded to Wonderboom Aeramente to reach the service agents. The landing at Wonderboom was executed carefully, using a trolley jack and wooden blocks to support the aircraft where the gear was missing. No injuries were reported, and the detached wheel assembly was recovered from the Germiston Golf Course.
The investigation
SACAA AIID investigators examined the fractured wheel axle to determine the cause of the separation. Metallurgical analysis performed by specialists revealed that the fracture occurred within the threaded region of the axle. Microscopic examination of the fracture surface showed a coarse, crystalline appearance, which is characteristic of a brittle fracture mode.
Scanning electron microscopy (SEM) confirmed that the failure was primarily intergranular cleavage, suggesting the metal had failed under sudden, intense pressure. While investigators looked for signs of pre-existing fatigue cracks, they found no evidence of such defects. The investigation also considered the possibility of stress corrosion cracking due to the nature of the cadmium-plated high-tensile steel used in the component.
Findings
- The primary cause of the incident was an instantaneous brittle overload failure of the outer section of the wheel axle.
- The failure occurred at the threaded area of the axle, which secured the wheel to the gear assembly.
- The fracture was likely triggered by an impact during a previous landing.
- There was no evidence of pre-existing fatigue or manufacturing defects on the fracture surface.