HAYESVILLE, NC, USA
N6191N
CESSNA T210N
ABOUT 30 MINUTES INTO THE FLIGHT, THE PILOT REPORTED A COMPLETE LOSS OF ENGINE POWER. WHILE MANEUVERING FOR AN EMERGENCY LANDING TO A PUBLIC ROAD, THE PILOT SPOTTED AN OPEN FIELD AND COMPLETED A FORCED LANDING. EXAMINATION OF THE ENGINE ASSEMBLY DISCLOSED THAT NUMBER TWO EXHAUST VALVE FAILED IN FATIGUE AT THE RADIUS BETWEEN THE VALVE STEM AND THE VALVE HEAD. THE METALLURGICAL EXAMINATION REVEALED A DECREASE IN THE HARDNESS OF THE HEAD END OF THE VALVE, LOSS OF THE CHROMIUM PLATING OVER MUCH OF THE LENGTH OF THE VALVE STEM AND EXCESSIVE WEAR OF THE CENTER PORTION OF THE VALVE STEM. THE VALVE STEM WAS DARKLY COLORED, NORMALLY ASSOCIATED WITH HIGH TEMPERATURES, OVER ONE HALF THE LENGTH OF THE VALVE STEM. THE PART NUMBER STAMPED ON THE EXHAUST VALUE CORRESPONDED TO AN AFTER-MARKET SUPPLIER'S NUMBER.
On January 19, 1994, at 2030 eastern standard time, a Cessna T210N, N6191N, collided with the ground while the pilot attempted an emergency landing in a field near Hayesville, North Carolina. The business flight operated under 14 CFR Part 91 with a valid instrument flight clearance. Visual weather conditions prevailed at the time of the accident. The airplane sustained substantial damage, and the two occupants were not injured. The flight departed Asheville, North Carolina, at 1946 hours. The pilot telephoned Raleigh Flight Service Station and obtained a weather briefing for an instrument flight from Asheville, North Carolina, to Fort Payne, Alabama. Upon completing the pre-flight briefing, the pilot filed an instrument flight plan. The pilot was issued an instrument flight clearance and cleared for takeoff on runway 16. Upon reaching 10,000 feet, the pilot radioed air traffic control and requested 10,000 feet for the cruise altitude (see attached chronological summary of flight). At 2018, three minutes after the pilot switched the fuel selector, the pilot of N6191N radioed Atlanta Center and reported a fuel problem; he also stated that he needed to get on the ground because the engine was losing power. The controller informed the pilot of several possible landing sites but the pilot did not see them or they were too far away from his position. The pilot asked the controller if there was a road or interstate highway near his location. According to the controller there should have been an interstate highway near. At approximately the same time, the pilot noticed a car on the road near his position. As he descended within two hundred feet of the road, he realized that a safe landing was not possible; he executed a left turn toward a pasture which he had seen seconds earlier (see attached pilot aircraft accident report). The pilot completed an emergency landing to the pasture. The examination of the engine assembly disclosed that the number two cylinder exhaust valve fractured in fatigue. The valve stem fractured near the beginning of the radius between the stem and the head of the valve. The Metallurgical examination revealed a decrease in the hardness of the head end of the number two exhaust valve, a loss of the chromium plating over much of the length of the valve stem and excessive wear to the center portion of the valve stem. Commensurate with high temperatures, the stem was darkly colored over one half its length. The diameter of the exhaust valve stem was measured at six equally spaced locations along the stem from the rocker arm to the head with the following results: 0.434 inch, 0.433 inch, 0.425 inch, 0.421 inch, 0.425 inch, and 0.430. Information supplied by a representative of Teledyne Continental Motors indicated that the stem of the valve is hard chrome-plated and had a specified finishing diameter of 0.4333 inch to 0.434 inch. Stamped on the rocker shaft end of the valve stem was the part number PA 637781; this part number corresponded to an after-market supplier (not Teledyne Continental Motors, the original engine manufacturer). The microstructure of the valve corresponded to the original manufacturer specifications (see attached Metallurgist' Factual Report). A review of the aircraft maintenance logs revealed that on June 18, 1990, the engine was rebuilt at 1396 airframe hours. On July 20, 1992, at 2094 airframe hours, numbers 4 and 5 cylinders were replaced. On March 25, 1993, at 2274 airframe hours, numbers 1, 2, 3, and 6 cylinders were replaced. The accident occurred 1138 hours since the last major engine overhaul and 264 hours since the installation of number 2 cylinder (see attached aircraft maintenance logs).
THE FATIGUE FAILURE OF NO. 2 EXHAUST VALVE WHICH RESULTED FROM EXCESSIVE HEAT AND WEAR TO THE VALVE STEM. A FACTOR WAS THE DARK NIGHT.
Source: NTSB Aviation Accident Database
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