MOSQUITO FLATS, AK, USA
N5200X
CESSNA 206
THE ENGINE OIL PRESSURE BEGAN TO DROP AND THE TEMPERATURE BEGAN TO RISE. BEFORE THE PILOT COULD RETURN TO TOK, ALASKA, THE ENGINE STOPPED PRODUCING POWER AND WOULD NOT WINDMILL. THE ENGINE DISASSEMBLY SHOWED THAT THE NUMBER 6 CYLINDER PISTON PIN CAP WAS MISSING AND THAT THE NUMBER 6 CYLINDER CONNECTING ROD CAP WAS FRACTURED INTO THREE MAJOR PIECES. ALL BEARING SURFACES SHOWED SIGNS OF HEAT DAMAGE. THE AIRPLANE WAS FORCED TO LAND ON MUSKEG AND NOSED OVER DURING THE LANDING ROLL.
On August 5, 1994 at 1450 Alaska daylight time, a wheel equipped Cessna 206 airplane, N5200X, registered to and operated by 40 Mile Air LTD, of Tok, Alaska, experienced a rise in oil temperature, a drop in oil pressure, and a subsequent engine stoppage during cruise flight. The flight was forced to land on Mosquito Flats and nosed over during the landing roll. The air taxi flight, operating under 14 CFR Part 135, departed Tok for a local flight. Visual meteorological conditions prevailed and a company flight plan was in effect. The pilot and the passenger were not injured and the airplane received substantial damage. According to the pilot, he saw a rise in oil temperature and a drop in oil pressure. He immediately reversed course to return to Tok. The engine stopped producing power before reaching the airport and he was forced to land on the muskeg. Examination of the engine showed that the number 6 cylinder piston pin cap was missing. The number 6 connecting rod cap was found broken in three major pieces and numerous smaller pieces. According to John Lauer, Customer Service Representative for Superior Air Parts, the number on the piston pin identifies the pin as a German manufactured piston pin and the Service Bulletin, which recalls the Superior Air Parts Piston Pin number SA520046, does not apply to that installed piston pin. Mr. Lauer stated that in the past, and as a result of his experiences, the reasons for piston pin failures could be misalignment, rod fit/pin fit in small end of rod bushing, a bent or twisted connecting rod, too much endplay (thrust washer), infrequent oil changes which would allow the pin to bind up, and wear in the bushing in the rod. The examination of the engine could not show which of these situations applied. Mr. Lauer stated that this event occurred in a relatively brief period of time, and that the metal introduced into the engine resulted in oil starvation.
THE MISSING NUMBER 6 CYLINDER PISTON PIN CAP AND THE SUBSEQUENT FAILURE OF THE NUMBER 6 CYLINDER CONNECTING ROD CAP. ALSO, THE LACK OF SUITABLE LANDING AREA FOR THE FORCED LANDING.
Source: NTSB Aviation Accident Database
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