What happened
On August 21, 1970, a pilot attempted a private VFR flight from Zurich to Frankfurt in a Cessna 172 H, registration D-ENBB. Although weather briefings indicated favorable conditions north of Basel, conditions around Zurich were deteriorating. The pilot requested a special VFR clearance to exit the Zurich control zone, eventually receiving an approved route via Schlieren and Bremgarten.
After departing Zurich at 15:03 CEST, the pilot navigated through Schlieren and Bremgarten. Seeking to continue toward the Koblenz NDB and Basel, the pilot turned northward. However, encountering heavy clouds and reduced visibility, the pilot attempted to navigate via the Limmat Valley. During this maneuver, the aircraft entered thick cloud cover and struck the southern slope of the Lägern ridge, approximately 70 meters below the crest. The impact resulted in the destruction of the aircraft, though the pilot survived with minor injuries.
The investigation
The investigation examined the pilot's flight preparation, the communication between air traffic controllers, and the prevailing meteorological conditions. It was established that the pilot had checked the weather multiple times, but conditions worsened during the flight, with increasing rain and lower cloud bases.
Investigators identified significant confusion regarding the approved flight route. Due to a misunderstanding during the initial briefing, the pilot was provided with instructions that conflicted with his intended path. Furthermore, while a radar controller observed the aircraft turning back toward the Zurich control zone and expressed concerns about the flight path toward the Lägern ridge, the tower controller did not relay these concerns to the pilot. The pilot's position report of "across Baden" was noted as being too vague to provide clear situational awareness.
Findings
- The pilot experienced a loss of geographical orientation due to the challenging terrain and poor visibility.
- The flight was conducted with visibility levels below the required minimums for VFR operations.
- Inadequate navigational preparation for the route exiting the control zone contributed to the error.
- The aircraft struck terrain that was obscured by clouds.