CHI95LA225

The pilot reported that he noticed an engine vibration about 10 minutes after takeoff, and returned to Williston to make a precautionary landing. While approaching the downwind leg for runway 29 the engine seized. He was unable to make a runway landing so he attempted to land on the airport property. He saw hay bales and equipment where he intended to land, and manuevered to avoid the bales. The airplane stalled in a near level attitude, impacting the runway berm. Examination of the engine revealed that the fuel system was running rich at low power settings, but lean at high power settings. The fuel pump was delivering 22 psi of fuel pressure instead of the 34 psi specified. The examination of the number four piston revealed that it was severely eroded around the perimeter of the piston, typical of combustion chamber detonation.

On July 16, 1995, at 0814 central daylight time, a Cessna 206, N29000, sustained substantial damage during a forced landing due to loss of engine power near Williston, North Dakota. The commercial pilot reported no injury to himself or to the four passengers. The 14 CFR Part 91 flight departed Sloulin International Airport, Williston, North Dakota, en route to Lethbridge, Alberta, Canada. Visual meteorological conditions prevailed and an instrument flight plan was filed.

The pilot reported that he had recently purchased the airplane and had flown about 17 hours in the airplane prior to the accident flight. He reported that the engine appeared to run smoothly and develop approximately normal power considering the temperatures and humidity.

The pilot reported that on July 16, 1995, he departed runway 29, Sloulin International Airport, Williston, North Dakota, at about 0802. He reported that at about four miles from the airport he noticed a very slight engine vibration. He reported that he changed fuel tanks, turned the fuel pump on and off, moved the mixture both richer and leaner, changed the manifold pressure and RPM, and checked the magnetos, but nothing seemed to change the vibration. At about 6 to 8 miles from the airport, he decided to return to the airport. He reported that he monitored the fuel flow, cylinder head temperature (CHT), exhaust gas temperture (EGT), oil pressure, oil temperature, manifold pressure, RPM, and all indications appeared normal.

The pilot reported that the vibration continued the same until he was about 1 1/2 miles from the runway, approaching a left downwind to runway 29 when the engine seized. He realized he could not make either runway 29 or 02, and he elected to try to make the airport property. He reported that when he cleared the airport fence, he saw that his intended area of landing was obstructed with round haybales and haybaling equipment. He reported that he added flaps and turned in order to clear the machinery. He reported that the airplane landed in a nearly level, full stall condition. The airplane hit hard on the upslope of the runway causing the aircraft's belly to scrape solidly with the ground. The airplane bounced again before rolling up on the runway and coming to a stop.

After the accident the pilot checked the oil and the dipstick indicated that there was no oil. He reported that prior to the accident, the airplane had used only one quart of oil in about the last 17 hours of flight.

An Airworthiness Inspector from the Federal Aviation Administration inspected the aircraft and reported that the number four piston had melted down, and a hole had burned through the piston near the rings. He reported that the melted aluminum had blown into the exhaust system and into the muffler. He reported that the CHT probe measured the temperatures from the number three cylinder, and that the EGT probe measured temperatures from the left exhaust manifold. He also reported that fuel samples were taken and showed no signs of contamination.

An engine teardown was performed for further examination. The examination revealed that the number 1, 2, 3, 5, and 6 cylinders had corrosion on the cylinder walls. All the exhaust valves were redish orange in color. The number four piston was damaged by the breakdown of the metal and had contaminated the cylinder. The examination revealed that the engine had seized and that the transfer collar had seized on the crankshaft. The magnetos were checked and they operated normally.

The fuel pump was bench tested and the examination revealed that the pump was running rich at low power settings, but lean at high power settings. At 2600 RPM the fuel pump was delivering 22 pounds per inch (psi) pressure vice the 32 psi called for in the specifications. The fuel nozzles flow tested within specifications. The fuel pump was torn down for further examination and it revealed that the pump vanes were slightly loose, but no major defect was noted.

The number four piston and cylinder were sent to the Materials Laboratory of the National Transportation Safety Board for examination. The Materials Laboratory reported that the head of the number #4 piston was severely eroded around the perimeter from the combustion chamber surface to the insert for the first compression ring. The report stated that the erosion appeared typical of combustion chamber detonation.