What happened
On September 26, 2013, an EC 120 B helicopter, registration SE-JHH, was performing aerial work as part of a reindeer herding operation approximately 85 km north of Kiruna. The flight was transporting a quad bike via a sling load. During the mission, the pilot initiated a left turn that transitioned the aircraft from a crosswind into a tailwind. This change, potentially compounded by a downdraught from the local terrain, caused the loss of translational lift.
As the helicopter began to descend, the quad bike made contact with the ground and started to drag. The resistance from the load prevented further flight, causing the helicopter to strike the terrain and settle on its side. While the engine was shut down and the crew—which included two passengers and a canine—successfully evacuated, one person sustained minor injuries and the aircraft was substantially damaged.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the wreckage and analyzed GPS and flight data. Technical inspections of the EC 120 B revealed no mechanical malfunctions or issues with the cargo hook system prior to the accident. The investigation also reviewed the pilot's training records and interviewed the crew and company management. Investigators looked into the meteorological conditions, noting gusty winds from the north and northeast, and evaluated the pilot's decision-making process during the emergency.
Findings
- The primary cause of the accident was the underestimation of the assignment's degree of difficulty.
- The pilot misjudged the wind direction, leading the aircraft into a tailwind component that ceased translational lift.
- A misjudgment of the terrain inclination occurred, likely due to visual illusions caused by irregular snow cover and a lack of distinct horizon.
- The pilot did not initiate the emergency release of the sling load, likely because he was focused on maintaining flight control and had not previously practiced the emergency release in a live or simulated situation.
Safety action
To prevent similar occurrences, the SHK recommended that the Swedish Transport Agency ensure operators conducting sling load operations include practical exercises of simulated emergency releases within their training programs.