What happened
On the morning of June 24, 1979, a private VFR flight departed from Beromünster in a Piper PA-38-112 Tomahawk, registration HB-PCP. The flight's purpose was to allow a passenger to take aerial photographs of his property near Schwarzenberg. After flying over the town at a low altitude, the pilot entered the Giessbach valley, heading south.
As the terrain within the valley became increasingly steep, the pilot realized the aircraft was struggling to maintain altitude. In an attempt to increase lift, the pilot extended the flaps. However, the aircraft's climb performance was insufficient to clear the rising ground. The aircraft struck the top of a tree with its left wing and subsequently crashed into marshy terrain from a height of approximately 20 meters. Both occupants sustained slight injuries, while the aircraft was destroyed.
The investigation
The investigation examined the aircraft's condition, the pilot's credentials, and the environmental factors at the time of the accident. The Piper PA-38-112 was a relatively new aircraft, having been imported from the United States in late 1978 with approximately 88 flight hours. The investigation confirmed that the aircraft was airworthy, with weight and balance within permissible limits.
At the crash site, investigators found the flaps fully extended and locked, the engine at full power, and the mixture set to rich. The weather conditions were characterized by good visibility (over 15 km) and a cloud base of approximately 2,000 meters. The investigation found no evidence of mechanical failure or pre-existing defects in the aircraft.
Findings
- The pilot entered a narrow valley at an altitude that did not allow for a safe escape maneuver or a 180-degree turn.
- The pilot was likely distracted by the passenger performing aerial photography.
- The increasing gradient of the valley terrain eventually exceeded the aircraft's ability to climb, leading to a loss of airspeed and a likely stall.
- The survival of the occupants was attributed to the soft, marshy ground and the use of three-point safety harnesses.