What happened
A helicopter was engaged in an operation to string ropes and wires. The crew consisted of a pilot in command in the left front seat, a copilot in the right front seat, and two observers seated behind the pilots on either side. During the mission, the aircraft approached a 150-foot tall pole where a workman was positioned at the top. The objective was for the workman to connect a rope to a 17-foot line descending from the helicopter, which carried 600 lbs of weights.
A ground operations foreman was observing the maneuver from the ground between his vehicle and the pole. While the vehicle was radio equipped, there was no radio communication between the pilot and the ground crew during the period the helicopter was overhead.
Witnesses observed the helicopter approaching the pole from above with its nose facing northwest. At the time of the incident, the wind was from 110 degrees at 9 knots, gusting to 19 knots. The copilot was on the controls, receiving directional suggestions from the observer on the right side of the aircraft. As the helicopter maintained a high hover over the pole, the workman attempted to attach the rope. During this process, the helicopter descended while drifting left and forward of the pole and the workman. The aircraft then began to back up and climb, causing the rotor blades to strike both the pole and the workman. Following the strike, the helicopter rolled to the right, descended, and impacted the ground on its right side.
Findings
The investigation revealed that the specialized hook system typically used for this type of operation was unavailable because it was attached to a different helicopter. In its place, the crew utilized a 'U' shaped swivel hook featuring a bolt and nut arrangement. This substitute hardware prevented the workman from quickly attaching the rope to the aircraft as he would have with the standard system.
Video footage showed the helicopter hovering above the pole and the workman for approximately one minute and 15 seconds before the accident occurred. Additionally, although the operation manual requires two-way radio communication between the pilot and ground crew, no such communication was established during the critical phase of the maneuver.