What happened
On the afternoon of October 14, 1977, a SIAI-Marchetti S 205-18/R, registration HB-ELM, departed Ecuvillens for a local flight. Prior to takeoff, the pilot was twice warned by an instructor on the radio that rapidly advancing fog made flying conditions unsafe. Despite these warnings, the pilot departed at 16:38.
During the flight, the pilot contacted the airfield radio service to report his position near Matran. Due to the worsening weather, the radio operator advised the pilot to survey the airfield and divert to Gruyères if necessary. The pilot later reported his position over Corpata． Shortly after 17:00, witnesses observed the aircraft emerging from the fog at a very low altitude. While executing a left turn, the aircraft struck an oak tree approximately three kilometers northwest of the airfield. The impact tore off the right wing, causing the aircraft to crash onto its left side. The impact resulted in two fatalities.
The investigation
Investigators examined the wreckage and the flight sequence to determine the cause of the accident. The investigation confirmed that the aircraft's engine was producing high power at the moment of impact, and there was sufficient fuel remaining in the tanks to reach an alternate airfield. The aircraft's weight and center of gravity were within permissible limits.
Technical analysis ruled out mechanical failure or fuel exhaustion as contributing factors. The investigation also noted that the aircraft's certificate of airworthiness had expired, though this was not a direct cause of the crash. Witnesses at the airfield confirmed that the pilot had been explicitly advised to divert to Gruyères, where visibility was much better, but the pilot proceeded with his approach toward Ecuvillens.
Findings
- Insufficient flight preparation, as the pilot failed to consult meteorological documents that would have predicted the deteriorating visibility.
- A poor assessment of changing weather conditions, leading the pilot to underestimate the severity of the incoming fog.
- The continuation of visual flight rules (VFR) in instrument meteorological conditions (IMC), which directly led to the collision with an obstacle.