What happened
On February 27, 2005, an EADS Socata Rallye 180 T, registration F-GBCH, was conducting a mountain flight instruction mission. The flight originated from Cannes, with the crew performing reconnaissance of several high-altitude airstrips (altisurfaces). Upon arriving at the Valberg airstrip, the crew performed several low and high reconnaissance passes and two landing circuits involving go-arounds.
During a third circuit, the engine experienced misfires at approximately 300 feet on final approach. The instructor, taking control, applied carburetor heat; however, because the engine power remained insufficient, the decision was made to land on the partially snow-covered runway. After landing safely and parking, the instructor conducted engine tests, which confirmed that all parameters were within manufacturer specifications.
Following the engine shutdown, the instructor inspected approximately 150 meters of the runway on foot. Observing that the left side of the strip was less contaminated by snow, the instructor decided to attempt a takeoff using that specific area. The aircraft initially accelerated normally, and the instructor began to lift the nose gear at approximately 60 km/h. As the aircraft entered a snow-covered section, it encountered significant braking force. The instructor attempted to abort the takeoff, but the sudden deceleration caused the nose gear to strike the ground with enough force to break it. The aircraft came to a stop roughly 100 meters before the end of the runway.
The investigation
The investigation focused on the engine performance during the approach and the surface conditions of the runway. Investigators determined that while the instructor was aware of the day's weather, the engine misfires were likely caused by moderate carburetor icing, which can occur during low-power maneuvers in specific atmospheric conditions.
Regarding the runway, the investigation established that the surface consisted of a layer of snow that had been hardened by successive freeze-thaw cycles. This resulted in a non-homogeneous layer that did not adhere uniformly to the ground, resting on patches of grass. This loose, friable snow layer created significant drag during the takeoff roll.
Findings
- The primary cause of the accident was the insufficient consideration of the runway condition during the takeoff decision.
- The pilot's decision-making process was rushed, leading to an attempt to use a contaminated strip of the runway.
- There was an inadequate assessment of the day's meteorological conditions, specifically regarding the impact of the snow on aircraft acceleration.
- The aircraft sustained damage to the landing gear.