What happened
On April 11, 2002, at approximately 08:53Z, two Bell 206B helicopters, registered ZS-HDV and ZS-HJY, were participating in a specialized flight test at the Win Helicopters helipad within the V&A Waterfront, Cape Town. The mission was a feasibility study requested by a stunt company to determine if a person could safely transition between two flying aircraft via a rope, a maneuver known as a "monkey walk."
The two aircraft were connected by a 32-meter rope attached to their respective cargo sling hooks. This rope was routed beneath the skid gear of both helicopters, angled forward at 45 degrees. Prior to the flight, the pilots confirmed that the release mechanisms for the rope—both manual and electrical—were fully operational.
During the ascent, the aircraft on the left lifted first, followed by the second aircraft. The flight plan intended for both helicopters to maintain a steady hover with the lowest part of the rope positioned roughly 2 feet above the ground. However, as the aircraft on the right began to lift, it drifted right of its intended reference point. This movement pulled the rope taut, triggering a sudden and violent roll-over of both aircraft. There were no injuries and no fatalities resulting from the incident.
The investigation
SACAA AIID investigators examined the mechanics of the tethered setup and the flight maneuvers leading to the instability. The investigation focused on the movement of the aircraft relative to their fixed reference points and the tension applied to the connecting cable. The inquiry confirmed that the release systems for the rope were functioning as intended prior to the event, but the pilot of the left-hand aircraft was unable to actuate the release once the roll began.
Findings
- The primary cause of the incident was that the pilot of the aircraft positioned on the right allowed the helicopter to drift from its reference point.
- This drift caused the 32-meter rope to become taut.
- The sudden tension in the rope created a dynamic roll-over effect that impacted both aircraft simultaneously.