What happened
On February 10, 1967, a Convair Metropolitan CV-440, registration HB-IMF, departed Zurich Airport at 07:43 CET for a training circuit. The flight was being conducted by an instructor accompanied by three student pilots as part of a type conversion program. While the flight was intended to be conducted under Visual Flight Rules (VFR), the terrain north of the runway—specifically the Lägerngsat ridge—was obscured by cloud cover.
Approximately three minutes after takeoff, during the initial climb, the aircraft deviated from its intended course. The aircraft entered a layer of clouds, transitioning from VFR to Instrument Flight Rules (IFR) conditions. Shortly thereafter, witnesses heard the aircraft strike trees on the Lägerngrat ridge. The impact resulted in the destruction of the aircraft and four fatalities, involving all occupants on board.
The investigation
The investigation examined the aircraft's flight path, the weather conditions, and the crew's actions. Investigators analyzed the terrain, which was covered in a light layer of snow, creating a low-contrast landscape that made ground references difficult to identify. Technical examinations of the Convair Metropolitan CV-440 engines, propellers, and instruments were conducted, as well as reconstruction flights to determine the aircraft's likely trajectory.
Findings
- The aircraft drifted from its original course, resulting in a lateral displacement toward the north.
- The crew encountered instrument meteorological conditions (IMC) after flying into a cloud cap covering the ridge.
- The lack of distinct ground landmarks, caused by the snow-covered landscape and low sun angle, likely prevented the crew from maintaining situational awareness regarding their position.
- It is possible that a student pilot, while attempting to correct a perceived bank, may have inadvertently initiated a turn in the wrong direction due to the different compass characteristics between the DC-3 and the CV-440.
- The decision to execute a left turn to exit the clouds and avoid the ridge likely contributed to the collision, as the aircraft was already significantly displaced from the runway axis.