What happened
On July 13, 1990, a Hughes 269C helicopter, registration HB-XKD, was engaged in commercial aerial photography operations for Aircolor SA in the Ticino region of Switzerland. The aircraft had been chartered from Robert Fuchs-Bamert and stationed at Locarno Aerodrome since June 16.
The incident occurred during a flight segment following a morning mission in Val Blenio. After refueling at Locarno for a subsequent assignment in the Mendrisiotto area, the pilot departed at 14:15 local time with a photographer on board. The aircraft first flew to Meride, located approximately 3.5 km northwest of Mendrisio, where the photographer captured images. Subsequently, the helicopter proceeded to Tremona, situated about 1 km south of Meride.
Upon reaching the area, the pilot conducted a three-minute reconnaissance at an altitude of 250 to 300 meters before beginning a descent for closer photography work. As the aircraft was maneuvering, the engine experienced a brief interruption. The pilot decided to land on a nearby meadow to allow the engine to cool and perform checks. After restarting the engine, he executed a hover in ground effect for three to four minutes to verify normal operation.
The pilot then initiated a climb to an altitude between 50 and 100 meters. Shortly thereafter, the engine failed again. Attempting to locate a suitable landing spot over rugged terrain, the rotor RPM decreased. The helicopter lost altitude, impacted trees, flipped forward, and struck the ground in a nose-down position. There was no fire. The photographer sustained serious injuries, while the pilot suffered only minor injuries.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the technical condition of the aircraft and the operational circumstances. The helicopter, built in 1986 with serial number 1217, had accumulated 1413 operating hours at the time of the accident. It was legally airworthy, with its last official status check performed on June 1, 1990. Maintenance records indicated that all airworthiness directives and service bulletins were up to date. The last 100-hour inspection had been conducted on April 30 at 1310 hours, meaning the next was due shortly after the accident flight.
Technical inspections revealed significant contamination in the main fuel tank. While the main fuel filter and the fuel injector filter were clean, the bottom of the tank contained numerous dirt particles of vegetable and animal origin, including insects. Crucially, the fuel was heavily contaminated with water. Approximately 2.5 liters of water were recovered from the tank after partial drainage at the accident site.
The pilot, a Swiss citizen born in 1963, held a commercial helicopter license and had logged 302 total flight hours, including 67 in the last 90 days. He was properly trained for aerial photography operations. A routine blood alcohol test ordered by local authorities returned negative results. Weather conditions were clear with good visibility, high pressure, and temperatures of 27°C.
Findings
The investigation determined that there were no pre-existing mechanical defects in the engine components such as the booster pump, mechanical fuel pump, fuel injector, or magnetos that could have caused the failure. Although the spark plugs showed signs of wear, they were deemed functional. The primary cause of the engine failure was identified as water contamination in the fuel system. The water likely accumulated in the tank sump and moved into the fuel supply during flight.
A contributing factor to the accident was the pilot's decision to continue the flight after observing irregular engine operation. Operating at low altitude over difficult terrain left little margin for error, preventing a safe autorotation landing when the engine failed completely.
Safety action
The investigation highlighted the importance of rigorous fuel management practices, particularly regarding moisture control. The aircraft flight manual explicitly instructed pilots to drain the fuel tank sump and fuel strainer for debris or water before flight and to refuel as soon as possible after landing to prevent moisture condensation. When refueling from questionable sources, careful filtration was required. These procedures were not sufficient to prevent the accumulation of water in this instance.