What happened
On 18 October 2008, a Robinson R44 II helicopter, registration ZS-HBS, was conducting a private pleasure flight through the Lydenburg district in Mpumalanga. After completing a game count at the farm Lepeng, the pilot and two passengers were en route to Rand Aerodrome when the aircraft entered a gorge adjacent to the Spekbog River.
A witness overlooking the valley reported hearing what sounded like a sudden loss of engine power, followed immediately by a large explosion and a plume of smoke. The aircraft had struck a high-tension electrical earth cable suspended across the valley. The impact caused the helicopter to strike a large rock and subsequently catch fire. The force of the impact and the ensuing post-impact fire resulted in three fatalities.
The investigation
SACAA AIID investigators examined the wreckage and the surrounding area to reconstruct the flight sequence. Although the aircraft was destroyed by the impact and fire, investigators identified scoring marks on the left-hand landing gear skid strut, indicating contact with the electrical cable. The investigation also found that a portion of the tail boom had been severed by the main rotor blades, likely due to a sudden, harsh control movement by the pilot attempting to avoid the wire.
While a witness perceived a loss of power, investigators determined that the change in sound was actually caused by the collision with the cable and the pilot's subsequent maneuvers. The investigation also noted that the high-tension line in question was an earth cable that was no longer in use, and the other two cables in the three-wire system had previously fallen to the ground. Crucially, the remaining earth cable lacked any high-visibility markers to alert pilots to its presence.
Findings
- The pilot was properly licensed, medically fit, and the aircraft was maintained according to regulations.
- The pilot did not see, or saw too late, the high-tension earth cable, leading to the collision.
- The accident was not survivable due to the extreme deceleration forces and the intensity of the post-impact fire.
- The electrical cable lacked any visual markings to indicate its position across the valley.
Safety action
- The SACAA recommended that pilots minimize unnecessary exposure to low-level hazards like power lines.
- The investigation suggested the development of a national database for pilots to track the locations of known power lines and tall structures.
- A recommendation was made for authorities to review policies regarding the marking of power lines that pose a risk to aviation safety.