What happened
On 22 July 1999, an Alouette III, registration ZS-RIH, was conducting a commercial aerial survey mission near the FADN area. The flight was part of an inspection of a newly established power line route, carrying a pilot and five passengers employed by Escom. While navigating a valley where a light domestic power line was positioned approximately 200 feet above the ground, the aircraft experienced a near miss with the wires.
At the time of the encounter, the pilot reported that the helicopter continued to operate normally, noting no unusual vibrations or abnormal sounds. The flight proceeded as planned, eventually returning to Virginia Airport (FAVG) in Durban.
The investigation
Following the completion of the mission, a post-flight inspection was conducted on the ZS-REH. During this check, the crew identified physical damage to the main rotor system, specifically noting strike marks on two of the three main rotor blades. One of these blades exhibited three distinct small indentations along its leading edge.
Upon discovering the damage, the pilot investigated the possibility of a wire strike. Subsequent communication with the Durban Metro Council Electricity Department confirmed that a power line had indeed been damaged in the specific geographic area where the survey flight had been conducted.
Findings
- The primary cause of the damage was an undetected strike with a power line during the survey operations.
- The pilot was unaware that a contact had occurred during the flight because the aircraft did not exhibit any immediate mechanical symptoms, such as vibration or noise.
- The power line involved was a light domestic line situated at a low altitude of roughly 200 feet within a valley.