What happened
On July 19, 1998, a privately owned Yakovlev YAK-18T, registration RA44490, departed from Raron aerodrome in Switzerland for a return flight to Hohenems, Austria. The aircraft was carrying two occupants during a VFR flight.
Shortly after takeoff, while the pilot was attempting to retract the landing gear at an altitude of approximately 30 to 50 meters, the engine experienced a significant loss of power. In an attempt to restore performance, the pilot utilized the manual engine priming pump to inject fuel directly into the cylinders, but this action proved unsuccessful. As the engine power continued to decline, the pilot declared a Mayday and requested landing priority for the opposite runway.
Realizing that returning to the aerodrome was no longer possible, the pilot executed an emergency landing in a nearby cornfield. During the final approach, the aircraft's tail section struck two lower wires of a high-voltage power line, and the left wing made contact with a second parallel line. The impact caused the wires to short-circuit, igniting a fire in the field. The aircraft sustained substantial damage, and the propeller blades were shattered.
The investigation
Investigators examined the engine and fuel systems to identify the source of the power loss. While the engine's M14P radial engine showed no obvious mechanical defects in the cylinders, valves, or ignition components, the investigation focused on the fuel supply. Analysis of the remaining fuel revealed a 3% diesel contamination, though experts noted this mixture was likely not sufficient to cause total engine failure on its own.
The investigation also reviewed the flight manual's emergency procedures. The manual instructs pilots to maintain a straight glide path and land ahead of the aircraft in the event of an engine failure during takeoff. The investigation noted that the pilot's attempt to use the manual pump may have been influenced by the fact that the engine was still producing enough power to maintain altitude and speed for a period, creating a false sense of possibility for a return to the runway.
Findings
- The primary cause of the accident was an emergency landing in unsuitable terrain following an engine malfunction immediately after takeoff.
- The specific cause of the engine power loss could not be definitively determined.
- The pilot attempted to use the manual priming pump to rectify the power loss, which likely delayed the decision to land straight ahead as prescribed by the flight manual.
- The aircraft struck high-voltage power lines, leading to a fire in the cornfield.