What happened
On June 24, 2019, an Airbus Helicopters AS 350 B3, registration OY-HGT, was performing a specialized sling operation in Greenland. The mission involved transporting a fuel tank from a barge in a fjord to a delivery point at the Telesite Dye One station on the mountain of Qaqatoqaq. To facilitate the delivery, the pilot utilized a 30-meter long line.
As the pilot approached the delivery point, the aircraft entered orographic clouds, which caused the pilot to lose all external visual references. This loss of visibility led to spatial disorientation and a partial loss of control. Fearing that the suspended fuel tank might strike personnel or infrastructure, the pilot initiated an abrupt rearward maneuver. During this period of instability, the fuel tank began striking the rocky terrain. The pilot eventually successfully released the cargo hook, but the helicopter continued a descending, nose-down path. The aircraft skids impacted the rocky terrain approximately 100 meters downhill from the target site, where the long line became entangled with rocks, causing the helicopter to come to rest on its right side. There were no injuries to the pilot.
The investigation
The Danish Accident Investigation Board (AIB Denmark) examined the flight history, meteorological conditions, and the pilot's operational environment. The investigation focused on the transition from visual flight rules to instrument meteorological conditions (IMC) during the maneuver. Investigators also reviewed the aircraft's technical status, finding no mechanical deficiencies, and analyzed the pilot's experience and the operational procedures for high-risk specialized operations.
Findings
- The primary cause of the accident was the entry into orographic clouds, which eliminated the pilot's external visual cues.
- The loss of visual references resulted in spatial disorientation and subsequent loss of control.
- The pilot's focus on the specific delivery point (a footbridge) required high precision and "head down" concentration, which likely hindered the perception of changing weather conditions.
- There was evidence of potential task fixation, as the pilot had been considering launching an additional sling operation before sunset, which may have influenced risk tolerance.
- The impact was survivable because the shallow angle of the skid impact and the tensioning of the long line helped dissipate the aircraft's forward energy.