What happened
On November 12, 1999, a Piper PA28-181 Archer III, registration HB-PNC, departed Grenchen Regional Airport for a private training flight. The pilot's intended route was toward Bulle and Thun. After climbing to approximately 9,500 feet AMSL, the aircraft flew over Lake Thun and followed the Kiental valley toward the Fründenjoch pass.
At approximately 14:52, a Swiss Air Force Pilatus PC-7 crew observed the aircraft performing slight rolling oscillations. Shortly thereafter, between 14:53 and 14:54, the aircraft struck the eastern face of the Galletgrat ridge at an altitude of approximately 9,980 feet AMSL. The impact resulted in one fatality and the total destruction of the aircraft. The wreckage was later located in the Fründengletscher area.
The investigation
Investigators examined the wreckage and reconstructed the flight path using military primary radar data. While the aircraft's transponder was not active, radar tracks showed the flight path through the region. The investigation included an analysis of the aircraft's structural integrity, engine, and control surfaces. No evidence of mechanical failure, engine malfunction, or pre-existing structural defects was found. The investigation also reviewed weather conditions, noting a southeast wind at 3,500 meters altitude that was nearly orthogonal to the ridge of the Fründenjoch.
Findings
- The pilot was in good health and was wearing both shoulder and lap belts at the time of the accident.
- The aircraft's weight and center of gravity were within permissible limits.
- The primary cause of the accident was inadequate mountain flying tactics.
- The aircraft encountered severe downdrafts or turbulence caused by the wind hitting the ridge, leading to a loss of control and subsequent terrain collision.
- The pilot's altitude provided only a very slim margin of safety (approximately 200 feet) above the terrain when entering the turbulent zone.
Safety action
It is recommended that the Federal Office of Civil Aviation (FOCA), in coordination with air traffic services and aircraft operators, improve the systems and procedures used to identify overdue aircraft more rapidly to ensure timely search and rescue activation.