Accident Overview
On 21 August 1970, at approximately 1517 MEZ, a Cessna F 172 H registered D-ENBB collided with terrain on the south slope of the Lägern ridge, about 70 meters below the crest and 1,100 meters west of the Lägern-Hochwacht mountain hut. The pilot, a German national born in 1931, held a valid private pilot license and had logged 208 total flight hours, including 106 hours on the accident type. The aircraft was airworthy with no technical defects found; weight and balance were within limits.
Flight History
The pilot planned a VFR private flight from Zurich to Frankfurt. Weather briefing indicated good conditions north of Basel but poor weather near Zurich Airport. At 1503 MEZ, he departed runway 28 with a special VFR clearance. Initially assigned a route, the pilot requested and received a different routing via Schlieren and Bremgarten. After reporting over Bremgarten at approximately 1511, he was released from the tower frequency. The pilot then attempted to navigate toward Koblenz NDB and Basel, turning north. At 1514, he reported "abeam Baden" at 2,500 ft QNH. He later said he followed the Limmat valley northeast but was hampered by clouds and poor visibility. The aircraft entered clouds and struck the terrain at 1517.
Weather Conditions
At the time of the accident, weather in the Zurich control zone was generally poor. Cloud base over the airport was around 3,000 ft with scattered lower clouds. Moderate rain fell, visibility was 3.5 km. In the accident area, hill clouds covered the Lägern ridge completely.
ATC Involvement
A radar controller in the approach unit observed the flight track and noted the aircraft turned north after Bremgarten. Concerned about the Lägern terrain, he alerted the tower controller, who did not share those concerns. The aircraft had already been released from frequency and did not respond to subsequent calls.
Probable Cause
The investigation concluded that the accident was caused by: inadequate and partly misguided navigational preparation for the departure from the control zone; loss of geographic orientation in bad weather; failure to maintain prescribed minimum visibility; and impact with a terrain obstacle shrouded in clouds.