What happened
On March 18, 2017, a privately owned Robinson R44, registration JA7907, was conducting a leisure flight near Odaira, Itoigawa City, in Niigata Prefecture. The aircraft, carrying a pilot and three passengers, was attempting to land at a temporary airfield.
During the approach, the pilot deviated from the approved flight path. Instead of following the established approach direction, the pilot attempted to land by performing a steep left turn and a nose-down maneuver directly over the helipad. To avoid nearby trees, the pilot increased the bank angle, which caused a rapid loss of altitude. During this maneuver, the low rotor RPM warning horn activated. As the aircraft continued to descend, the left side of the rotorcraft struck a snowy slope approximately 20 meters from the helipad. The impact caused the main rotor to catch in the snow, resulting in a roll-over that stopped the engine and destroyed the airframe. There were no fatalities and no injuries were reported among the four occupants.
The investigation
The Japan Transport Safety Board (JTSB) examined flight footage, photographs, and statements from the pilot and passengers. The investigation focused on the flight path, the pilot's maneuvers, and the environmental conditions at the landing site. Investigators also reviewed the approved landing procedures for the temporary airfield and the impact of the snowy terrain on the pilot's depth perception.
Findings
- The pilot's approach involved a steep left turn and a nose-dive, which was a departure from the safety procedures outlined in the airfield's application.
- The pilot likely experienced a featureless terrain illusion; because the snow-covered ground lacked distinct landmarks or defined boundaries, the pilot misjudged the aircraft's actual altitude.
- The activation of the low rotor RPM warning horn indicated that the pilot's sudden collective input to avoid trees had compromised the rotor's stability.
- The aircraft's damage was exacerbated by the process of moving the wreckage from the accident site using a snow compaction vehicle.