What happened
On February 16, 1993, an Agusta A-109 K2 helicopter, registration HB-XWE, was being ferried from Gsteigwiler to Zurich for final equipment installations. The pilot, a REGA mechanic with a professional pilot license, was operating the aircraft alone. During the flight, the aircraft's behavior became erratic. Witnesses on the ground observed the helicopter flying at extremely low altitudes, sometimes as low as 40 to 50 meters, navigating dangerously close to high-voltage power lines.
As the aircraft approached the area of Cham, it performed a 90-degree turn toward Lake Zug. After a period of stable flight at approximately 130 meters, the helicopter suddenly pitched forward into a steep, nearly vertical dive. The aircraft struck the surface of Lake Zug at approximately 125 knots and sank to a depth of 30 meters. The pilot sustained one fatality.
The investigation
Investigators examined radar data from the Emmen military airfield, which showed the aircraft intermittently disappearing from radar due to its low altitude. Eyewitness accounts from farmers and motorists described a "erratic" and "uncontrolled" flight pattern. Technical analysis of the wreckage confirmed that the engines were functioning correctly and that the aircraft was mechanically airworthy at the time of the accident. Evidence showed the pilot actually attempted a "flare" maneuver just before impact, suggesting an attempt to mitigate the crash.
Medical and psychiatric reviews were also conducted. The investigation looked into the pilot's medical history, specifically regarding chronic migraines, and the communication protocols between treating physicians and aviation medical authorities.
Findings
- The primary cause of the accident was likely health problems involving the pilot, specifically a migraine attack that resulted in significant visual field restrictions.
- The pilot's medical records indicated a history of migraines that could lead to loss of vision, yet this was not fully disclosed during recent medical examinations.
- The low flight altitude caused the aircraft to disappear from military radar tracking.
- There were no technical failures or mechanical defects found in the Agusta A-109 K2.