What happened
On February 10, 1980, a pilot departed from Annemasse airfield in a Robin HR 200/100, registration F-GAEB, for a scheduled training flight. Shortly after reaching an altitude between 2,000 and 2,500 feet near Douvaine, the engine experienced a progressive loss of power. In an attempt to rectify the issue, the pilot engaged the carburetor heat, but this resulted in a further drop in engine RPM, leaving the engine running at only 1,700 RPM.
To avoid flying over densely populated areas, the pilot attempted an emergency landing in a field near Presinge. During the maneuver, the pilot attempted to select a different landing site because the initial field appeared too soft. This change in course led to a loss of airspeed, causing the aircraft to stall at a low altitude. The aircraft struck the ground on its right wing, resulting in the destruction of the aircraft and one serious injury to the pilot.
The investigation
The investigation examined the engine components and the environmental conditions at the time of the accident. While investigators found some mechanical irregularities in the rocker arms of cylinders 1 and 3, these were determined to be post-crash damage rather than the cause of the power loss. Analysis of the spark plugs revealed heavy black soot, indicating an excessively rich fuel mixture.
Meteorological data showed high humidity (80%) and temperatures around 8°C, which are conditions highly conducive to ice formation. The investigation also looked into the cockpit safety features, noting that while the cabin remained largely intact, the pilot's injuries were exacerbated because the lap belt anchor failed upon impact and the aircraft was not equipped with shoulder harnesses.
Findings
- The primary cause of the accident was a low-altitude stall during an emergency landing attempt.
- The engine power loss was likely caused by carburetor icing.
- The use of carburetor heat may have inadvertently worsened the situation by further enriching the fuel mixture with less dense, warm air.
- A late-stage change in the landing target contributed to the loss of airspeed and subsequent stall.
Safety action
Following the investigation, recommendations were made to re-examine aviation standards regarding seat belt safety, specifically focusing on the strength of attachment points and the mandatory installation of shoulder harnesses to prevent head injuries during impacts.