What happened
On February 9, 2015, a Schweizer S-269C helicopter was conducting basic training maneuvers at Wels Airfield (LOLW) in Austria. The flight, operated by an Approved Training Organisation, involved a flight instructor and a student pilot. The flight began with standard procedures, including a pre-flight inspection and refueling.
During the training session, the crew performed several maneuvers involving a "Quick Stop" technique, which involves using cyclic control to pitch the nose up to bleed off forward airspeed and transition into a hover. While performing this maneuver near the threshold of runway 27 Grass L, the instructor reduced engine RPM to facilitate a rapid opening of the freewheel. During this phase, the engine suffered a sudden failure.
At the same time, the aircraft was experiencing a tailwind component due to prevailing wind conditions. The combination of the engine failure and the wind caused an uncontrolled increase in the vertical descent rate. The instructor attempted to mitigate the descent by pitching the nose forward into a roll-over maneuver, but the aircraft struck the edge of taxiway B at approximately 10 knots forward speed. The helicopter slid roughly 40 meters before coming to a halt. There were no injuries to the crew, and both individuals were able to exit the aircraft independently.
The investigation
The Austrian Federal Safety Investigation Board (SUB) examined the aircraft, the flight records, and the environmental conditions at the time of the accident. The investigation focused on the mechanical state of the Lycoming HIO-360-D1A engine, the impact of the weather, and the execution of the "Quick Stop" maneuver. Investigators also reviewed the meteorological data from the Wels-Schleissheim station and the flight school's operational procedures.
Findings
- The investigation could not identify any pre-existing mechanical defects in the engine that would have triggered the failure, though the reduction in RPM during the maneuver made an engine shutdown a possibility.
- Tailwind gusts contributed to an abrupt increase in the aircraft's sink rate during the maneuver.
- The presence of snow on the lower cockpit windshield likely hindered the pilot's ability to maintain an accurate visual reference to the ground.
- The investigation noted that the specific methodology of using a "Quick Stop" to decelerate before a 180-degree turn was not considered a standard or easily justifiable practice by the investigators.
- The aircraft was within its weight and balance limits, and the crew members were properly licensed and qualified for the flight.