What happened
On March 18, 2019, a Robinson R44, registration LN-OGT, was attempting a private departure from a parking area near the Uvdal Alpinsenter in Norway. The pilot had delayed the flight from the previous day due to engine starting difficulties caused by cold weather. After a successful warm-up period, the pilot lifted the aircraft into a low hover, intending to turn the nose left to take off against the wind.
During the hover, the aircraft became unstable around the yaw axis. Despite applying full left pedal input, the helicopter began rotating rapidly to the right. The pilot attempted to abort the takeoff by lowering the collective to return to the ground. However, as the skids made contact with the surface, the aircraft suddenly swung to the left. This movement caused the tail rotor and vertical fin to strike a snow-covered slope, resulting in significant structural damage to the tail section. There were no injuries to the single occupant.
The investigation
The Norwegian Safety Investigation Authority (NSIA) examined the meteorological conditions and the aircraft's flight dynamics. Investigators analyzed wind data from nearby stations, which revealed that while the pilot perceived the wind as light during startup, the area was experiencing variable winds with gusts. Specifically, wind gusts of up to 38 knots had been recorded north of the site, and investigators concluded that sudden downdrafts or gusts of up to 40 knots could have impacted the area during the incident.
Findings
- The primary cause of the loss of directional control was likely Loss of Tailrotor Effectiveness (LTE), triggered by strong, variable winds from the northwest.
- The wind direction (between the 8 and 11 o'clock positions) is a critical configuration for this aircraft type, which can lead to a Tailrotor Vortex Ring State or main rotor disk interference.
- The pilot's attempt to correct the rightward rotation with increased left pedal input may have inadvertently worsened the situation by further reducing tail rotor efficiency.
- The aircraft had drifted approximately four meters to the right due to side winds before the collision occurred.
- The pilot's relatively limited experience, with 310 total flight hours and 182 hours on this specific model, may have contributed to the inability to abort the takeoff sooner.