What happened
On September 5, 1965, a flight instructor and a student were conducting a series of landings at various airfields following a flight from Zurich-Kloten. After landing at Altenrhein, the pilot intended to fly to Wangen-Lachen but departed without confirming landing availability, relying instead on a promise from ground staff that his arrival would be reported. Upon approaching Wangen-Lachen, the crew observed a "landing prohibited" signal and decided to divert to Schänis to request entry into the Zurich control zone.
At Schänis, the crew noted a warning signal regarding poor runway conditions, specifically muddy patches on the western side of the grass strip. While the northeastern section appeared intact, the pilot attempted a landing on that portion. Following an initial missed approach, the second landing attempt was completed at 17:45. After rolling approximately 50 meters, the Piper J3 Cub, registration HB-OVG, struck an unmarked, grass-covered swamp hole approximately 30 cm deep. The impact caused the aircraft to capsize and come to rest on its back. Both occupants escaped the accident uninjured.
The investigation
Investigators examined the runway conditions at Schän_nis, which was in poor state due to recent rain. The investigation established that while a warning signal for caution was present, the airfield manager had placed a "landing prohibited" signal on the ground between the aircraft's first and second approach. However, the crew did not notice this change in signal due to limited visibility during the left-hand turn of the missed approach and the unexpected nature of the signal change.
Findings
- The primary cause of the accident was the flight instructor's failure to verify landing availability at the intended intermediate airfield during flight preparation.
- The pilot relied on the assumption that his arrival at Wangen-Lachen would be communicated by ground staff rather than establishing direct contact himself.
- The aircraft encountered an unmarked, submerged depression in the grass runway that was obscured by vegetation.
- The crew failed to observe the updated prohibition signal during the second approach due to visibility constraints and lack of expectation regarding a change in signal status.