What happened
On May 13, 2018, a Reims Aviation F152, registration HB-CNK, was conducting a private VFR flight from Lugano to Buttwil. After stops in Genoa and Lucca, the aircraft departed Lugano for the return leg. While flying through the Leventina Valley toward the Gotthard Pass, the pilot encountered deteriorating visibility. Finding the Gotthard Pass obscured by clouds, the pilot decided to divert toward the Nufenen Pass, observing sunny conditions at the western end of the Bedretto Valley.
As the aircraft climbed through the valley, the cloud base continued to descend. The pilot performed several turns while attempting to gain sufficient altitude to clear the Nufenen Pass, which sits at 2,478 meters. During these maneuvers, the aircraft entered Instrument Meteorological Conditions (IMC). While flying in low visibility, the pilot executed a 180-degree turn at an altitude of approximately 5,600 ft AMSL, passing near high-voltage power lines. Despite applying maximum power, the aircraft's climb performance was insufficient to clear the rising terrain. At 15:57, the aircraft struck a snow-covered avalanche cone near Paltano. The impact caused the aircraft to flip onto its back. The pilot escaped without injury, while the passenger sustained light injuries.
The investigation
Investigators reconstructed the flight path using radar data, the aircraft's Flarm collision warning device, and tablet records. The investigation examined the pilot's pre-flight weather assessment, which relied on webcams rather than official meteorological reports. The team also inspected the engine's air filter, which was found to be heavily iced three hours after the accident. Furthermore, the investigation analyzed the aircraft's climb capabilities relative to the terrain and the pilot's flight maneuvers in the valley.
Findings
- The pilot's pre-flight weather assessment was overly optimistic, as he relied on local webcam images that contradicted official Swiss meteorological warnings and GAFOR forecasts, which had indicated that Alpine passes would be closed to VFR flight.
- The pilot demonstrated a lack of situational awareness and inadequate mountain flying training by attempting to navigate toward the Nufenen Pass without a concrete alternative plan or a strategy for a safe turnaround.
- The aircraft's climb performance was mathematically insufficient to clear the Nufenen Pass under the prevailing conditions, as the required climb rate was double what the Reims Aviation F152 could provide.
- The pilot entered IMC without instrument flight experience, significantly increasing the risk of controlled flight into terrain.
- The engine's air filter was heavily iced, suggesting that carburetor heat was not effectively utilized to prevent icing during the flight.