Accident Overview
On 7 June 1987 at 1045 local time, a Cessna U 206G, registration HB-CHK, operated by PARA-CENTRO Locarno SA, made an emergency ditching in Lake Maggiore approximately 2 kilometers west of Locarno airfield. The aircraft was destroyed in the accident. Three parachutists sustained very minor injuries; all occupants were rescued by a nearby boat.
Flight History
The pilot, a Swiss citizen born in 1959 holding a restricted professional pilot license, had accumulated 167:01 total flight hours, including 30:45 hours on type. On the day of the accident, the pilot departed Locarno airfield at 0900 for commercial parachute jumping operations. During the third flight, shortly after takeoff from runway 26R, the pilot initiated a left turn and simultaneously observed a sudden loss of engine power. The aircraft, powered by an Allison 250-C20S turbine, could not glide back to the airfield. The pilot elected to ditch in Lake Maggiore near the shore, touching down at approximately 65 knots. The aircraft carried seven occupants, exceeding its approved capacity of six.
Technical Investigation
The high-pressure compressor line (PC) between the fuel flow regulator and the compressor at the fuel control unit inlet was found fractured. Metallurgical examination by the Swiss Federal Laboratory for Materials Testing revealed the fracture resulted from corrosion fatigue. The crack initiated on the inner surface of the tube due to intergranular corrosion, facilitated by material not meeting manufacturer specifications: the steel contained higher carbon and lower titanium than required, making it susceptible to intergranular corrosion. This condition, combined with alternating mechanical stress, led to crack propagation from the interior outward, likely undetectable during visual inspections.
Cause
The accident was attributed to an emergency ditching necessitated by an engine failure following the rupture of the high-pressure compressor line.