What happened
On August 9, 2014, at approximately 09:18 UTC, a Schweizer 269C helicopter was performing a short commercial sightseeing flight from Stockerau Airfield (LOAU) in Austria. The flight, which included the pilot and one passenger, had returned to the airfield after visiting Burg Kreuzenstein.
During the final approach to runway 07, the pilot attempted to position the aircraft at a height of approximately 1.5 meters to facilitate landing, rotating the helicopter slowly to the right against the wind. During this maneuver, the aircraft experienced intermittent yawing. The pilot attempted to correct the movement using the pedals, but the helicopter suddenly began an uncommanded rotation to the right.
After approximately one and a half rotations around the vertical axis, the pilot managed to briefly stabilize the aircraft in a sideward flight toward 250 degrees. However, upon attempting to regain forward momentum, the pilot noted that the engine RPM had dropped below the permissible range. While attempting to maneuver away from parked aircraft near a hangar, the helicopter began rotating to the right even more rapidly. To avoid a collision with another helicopter parked on the landing area, the pilot attempted an immediate landing. The aircraft struck the ground hard and tipped onto its left side.
The investigation
The Austrian Federal Safety Investigation Board (SUB) examined the flight sequence, the aircraft's mechanical condition, and the environmental factors. The investigation focused on the aerodynamic conditions during the low-speed approach and the pilot's corrective actions. The investigation also reviewed the pilot's training and the technical characteristics of the Schweizer 269C regarding tailrotor performance.
Findings
- The primary cause of the accident was the pilot's failure to recognize a Loss of Tailrotor Effectiveness (LTE) event.
- The pilot initiated an incorrect maneuver to recover from the LTE.
- The aircraft suffered a hard landing due to the loss of directional control.
- Contributing factors included the generation of an unfavorable wind angle on the tailrotor during the rightward rotation at low forward speed, combined with high ambient temperatures.