History of the Flight
On 16 November 2020 at 1435 local time, the helicopter LN-OAX, an Airbus Helicopters AS 350 B3 operated by Heli-Team AS, was conducting a sling load operation delivering concrete for a pylon foundation for a new power transmission line at Songesand in Sandnes municipality, Rogaland County. The pilot was the sole occupant. During the operation, the pilot made an altitude correction at the pylon foundation, possibly due to a gust of wind, contact between the concrete bucket and the mast foundation, or a combination. Immediately after the correction, the pilot felt powerful vertical oscillations. He disconnected the suspended load and attempted to manoeuvre the helicopter out of the situation, but the helicopter crashed.
Injuries and Damage
The pilot evacuated the helicopter unassisted. No one was injured. The helicopter sustained significant damage.
Aircraft and Operator
LN-OAX was manufactured in 2002. It was owned and operated by Heli-Team AS Norge. The investigation reviewed the helicopter's technical systems and found no significant defects. The AS 350 helicopters delivered before 2006 may have servo configurations that make them more sensitive to rotorcraft-pilot coupling (RPC). Airbus Helicopters has published information and recommended replacing banjo screws with a smaller internal diameter to reduce sensitivity to oscillations.
Investigation
The Norwegian Safety Investigation Authority (NSIA) investigated the accident with assistance from BEA (France), Airbus Helicopters, and Safran Helicopter Engines. The investigation determined that the pilot lost control due to rotorcraft-pilot coupling (RPC), causing strong vertical oscillations. The phenomenon arose quickly, leaving the pilot insufficient time and altitude to regain control. The NSIA also referenced Airbus Safety Notices 3890-S-00 and 3899-S-97.