What happened
On May 31, 2009, a Discus b glider, registration HB-1912, was conducting a private VFR flight in the region of Gryon, Switzerland. After taking off via aero-tow and separating from the tug aircraft near Col de la Croix, the pilot proceeded with a flight primarily utilizing ridge soaring techniques.
During the flight, witnesses observing model aircraft in the area noted an unusual sound coming from the glider. One witness observed the aircraft performing a turn that became increasingly steep and nose-down. The aircraft continued this descending spiral, eventually impacting the ground at a near-vertical angle. The impact resulted in the death of the pilot and the total destruction of the aircraft.
The investigation
The investigation examined flight data from an onboard Colibri LX-Navigation recorder, witness testimonies, and the aircraft wreckage. Technical inspections of HB-1912 revealed no mechanical failures or defects that could have contributed to the accident. The aircraft's weight and center of gravity were within manufacturer limits, and the air brakes were found in a partially extended position, though this was likely due to the impact.
Medical examinations and an autopsy were conducted to assess the pilot's health. While the autopsy could not definitively identify an acute event like a cerebral hemorrhage due to the severity of the impact injuries, investigators found evidence of significant underlying health issues. The pilot suffered from hereditary polycystic kidney disease, which had progressed to end-stage renal failure.
Findings
- The primary cause of the accident was a collision with the terrain, which most likely resulted from the sudden incapacitation of the pilot.
- The pilot's medical condition, specifically advanced renal failure and associated hypertension, presented a high risk for sudden medical emergencies, such as a ruptured aneurysm.
- Although the pilot held a valid Class 2 medical certificate, the pilot had not informed the aviation authority (OFAC) of the progression of the kidney disease or recent major surgery for a malignant tumor.
- Meteorological conditions were generally stable, with only local thermal turbulence possible, and did not contribute to the crash.