What happened
On the afternoon of December 10, 1991, a pilot conducted a check flight in an Airbus Helicopters AS350 B2 Ecureuil (registration HB-XUY) accompanied by the aircraft's owner. Following this initial flight, which lasted approximately fifty minutes, the owner advised the pilot to practice autorotation procedures to maintain proficiency.
The pilot then embarked on a solo flight from Würenlingen toward Sitterdorf. In that area, he performed several slope approaches and three autorotation landings. He subsequently flew westward toward Amlikon in search of a suitable location for another exercise. Due to a low stratus cloud layer with a base at approximately 600 meters, the pilot was restricted from climbing higher than 160 meters (520 feet) above ground level.
At an indicated altitude of 1900 feet mean sea level (approximately 520 feet AGL), the pilot initiated an autorotation. With an indicated airspeed of only 60 knots, he pushed the cyclic stick slightly forward to accelerate toward the recommended 65 knots. This action increased both forward and sink rates. As the helicopter approached the ground, the skid guard struck the terrain, causing the aircraft to slide laterally and tilt forward. The main rotor then contacted the ground, leading to a 90-degree rotation before the helicopter came to rest on its back. The pilot shut down the turbine and exited the wreckage without assistance or injury.
The investigation
The Swiss Transportation Safety Investigation Board (STSB) examined the flight data, weather conditions, and operational context. The aircraft was certified for both private VFR day/night operations and commercial daytime use. At the time of the accident, the helicopter was in good technical condition, with mass and center of gravity within limits.
Weather reports from Zurich indicated a wind from the northeast at 5 to 10 knots. Because the pilot was flying westward during the landing phase, he experienced a tailwind component. The terrain elevation at the site was 420 meters above sea level. The pilot held a valid commercial helicopter license and had logged 293 hours of flight time, though recent activity was limited.
Findings
The investigation determined that the accident resulted from insufficient speed and altitude at the start of the autorotation combined with a late initiation of the flare phase. The pilot's attempt to increase airspeed by pushing the stick forward exacerbated the sink rate. The combination of low altitude, tailwind, and late flare prevented a controlled touchdown, causing the skid guard to hit the ground first. This contact destabilized the aircraft, leading to the rollover.
Safety action
No specific safety recommendations or regulatory actions are recorded in this report beyond the standard investigation process.