ERA19FA035 · Aerospatiale AS 355F2 F1

The pilot, pilot-rated passenger, and two linemen were conducting a flight to temporarily install a block (a large pulley used for fiber-optic wire) on a utility pole that was part of a set of high-tension power lines. The pilot was seated in the front right seat, and one of the linemen was seated outside of the helicopter on a bench that was externally attached to the right side of the landing gear. The pilot-rated passenger, who was observing the flight for training purposes, was seated in the front left seat, and the other lineman was seated in the aft left seat. The power lines were aligned northwest/southeast, which required the pilot to approach the utility pole on a southeasterly heading so that the pole would be to the right of the pilot and lineman. For the lineman to install the block on the utility pole, the pilot had to hover the helicopter next to the pole. The wind conditions about the time of the accident were such that the helicopter would have encountered a tailwind. The pilot-rated passenger, the lineman seated in the aft left seat, and witnesses on the ground all stated that, while the helicopter was hovering next to the utility pole, the helicopter's right skid struck the pole a few times. The helicopter rolled over, became entangled in energized power lines, and caught fire. All four of the occupants survived the impact with the power lines and jumped to the ground to escape the burning wreckage. The pilot and the lineman seated on the bench did not survive the fall.

A postimpact fire consumed most of the helicopter while it was entangled in the power lines, and sections of the helicopter dropped from the power lines as it burned. Examination of the wreckage and both engines revealed no preimpact mechanical deficiencies that would have precluded normal operation.

The surviving lineman stated that he had flown with the pilot earlier that day and that the pilot had difficulty keeping the helicopter steady due to the strong wind, so the lineman temporarily installed a block before the helicopter returned to the base. Before the accident flight, the pilots, linemen, their foreman, the owner and a representative of the helicopter company and representatives of the linemen's employer held a safety meeting and agreed that, although the wind was too strong to fully install a block, the wind was "okay" to temporarily install another block. Given that the pilot had difficulty holding the helicopter steady while hovering with a tailwind on the previous flight the pilot most likely also had difficulty hovering the helicopter with the tailwind that was present about the time of the accident. The helicopter's subsequent impact with the utility pole resulted in a dynamic rollover into the power lines.

Verbatim NTSB analysis and probable cause from the NTSB dataset