What happened
On June 29, 2024, at approximately 19:00 UTC, a Piper PA-18-150, registration LV-GBY, was conducting a general aviation ferry flight in the Chubut province of Argentina. The flight departed from a private airstrip at Estancia La Esperanza, near Cholila, destined for Lago Cholila.
While navigating a valley toward the lake, the aircraft flew at low altitude over the crest of Cerro Plataforma. During this phase of flight, the aircraft encountered orographic turbulence. In an attempt to find smoother air, the pilot initiated a descent to a lower altitude. During this maneuver, the aircraft's wheels made contact with the snow-covered, frozen surface of Lago Cholila. This sudden contact caused the aircraft to abruptly stop and capsize on the lake surface. The pilot, who was uninjured, abandoned the aircraft due to fears that the frozen surface might collapse under the weight of the fuselage. The pilot was rescued the following day via helicopter.
The investigation
The Argentine Transportation Safety Board (JST) examined the meteorological conditions and the operational environment of the accident. The investigation focused on the aerodynamic effects of the terrain on the flight path and the lack of standardized guidance for mountain operations in the region. Investigators analyzed the aircraft's configuration, noting it was equipped with large "bush wheels" designed for unprepared surfaces. The investigation also reviewed the pilot's training, noting significant experience in mountain flying obtained in Alaska, USA.
Findings
- The aircraft was subjected to orographic turbulence caused by wind interacting with mountain peaks.
- Specifically, southwest winds hitting the mountain faces created updrafts on the windward side and downward currents, known as subsidence or rotors, on the leeward side.
- The aircraft's wheels made unintentional contact with the frozen, snow-covered lake surface, leading to the sudden deceleration and subsequent capsize.
- There is a lack of national technical guidelines or official training materials in Argentina to assist general aviation pilots in planning and executing safe flights in mountainous terrain.
Safety action
To improve operational safety, the JST has issued a recommendation to the National Civil Aviation Administration (ANAC) to develop and publish an official technical reference guide for mountain operations. This guide should provide standardized criteria for flight planning, operational best practices, and training specifically tailored to the challenges of the Argentine cordillera.