FALL RIVER MILL, CA, USA
N5436Y
CESSNA T210N
AFTER LEVELING OFF AT CRUISE, THE ENGINE STARTED RUNNING ROUGH. A 2-INCH REDUCTION IN MANIFOLD PRESSURE RESULTED IN A METALLIC SOUND. ANOTHER 2-INCH REDUCTION RESULTED IN A LOUDER METALLIC SOUND. THE MANIFOLD PRESSURE THEN FELL TO 20 INCHES, THE OIL PRESSURE DROPPED TO ZERO, AND OIL BEGAN TO SPLATTER ON THE WINDSCREEN. A FORCED LANDING WAS MADE IN A LAVA FIELD SURROUNDED BY TREES. AFTER TOUCHING DOWN THE AIRCRAFT SLID AND NOSED OVER ON ITS BACK. POSTACCIDENT INSPECTION REVEALED THAT THE NO. 2 LOWER CONNECTING ROD BOLT HAD FRACTURED. MEASUREMENTS PERFORMED BY THE MANUFACTURER INDICATED THE ROD BOLT HAD BEEN UNDERTORQUED. THE ENGINE WAS LAST OVERHAULED 509 HOURS PRIOR TO THE ACCIDENT.
On June 11, 1995, at 1330 Pacific daylight time, a Cessna T210N, N5436Y, made a forced landing near Fall River Mills, California. The aircraft was destroyed. The certificated flight instructor received minor injuries and the student sustained serious injuries. The aircraft was owned and operated by Barry G. Miller & Associates Insurance Services, and was on an instructional cross-country flight when the accident occurred. The flight originated from the Cameron Airpark airport, Cameron Park, California, on the day of the accident as a round robin flight to Klamath Falls, Oregon. The aircraft departed Klamath Falls International Airport, Klamath Falls, Oregon, at 1305, with Willows, California, as the next planned stopover before returning to Cameron Park. Visual meteorological conditions prevailed at the time and no flight plan was filed. The student reported that after departing Klamath Falls International Airport they climbed to 9,500 feet msl. A few minutes after leveling off, the engine started running rough. When the student made a 2-inch reduction in manifold pressure both pilots heard a metallic sound. The student then reduced the manifold pressure another 2 inches and a louder metallic sound was heard. As the manifold pressure fell to 20 inches, the oil pressure gauge reading dropped to zero and oil began to splatter on the windscreen. The student then asked the instructor to take control of the aircraft. The instructor asked the student to make an emergency call on VHF 121.5 while he used Loran to attempt to locate an airport with gliding distance. After determining that all airports were beyond best rate of glide, the instructor asked the student to select the best available forced landing area. The student selected a lava field surrounded by trees. Once the instructor felt the landing was assured, he directed the student to lower the flaps and gear. After touching down, the aircraft slid about 140 feet and nosed over on its back. The long axis of the ground scars was oriented on a 226-degree bearing. The accident site was located at coordinates north 41 degrees 28.60 minutes, west 121 degrees 38.98 minutes at an elevation of 5,180 feet msl. The aircraft was found inverted on a heading of 060 degrees magnetic. The aircraft was intact with the exception of the landing gear. A main landing wheel with tire was found 87 feet from the aircraft on a 226-degree bearing. The nose landing gear strut was located 115 feet farther along in the direction of travel. A second main landing wheel with tire was found 30 feet from and abeam the left wing tip. The nose landing wheel and tire were not found. The lower front engine cowling exhibited evidence of crushing, scraping, and tearing. With the assistance of technical representatives from Cessna and Teledyne Continental, the engine and airframe were examined by an FAA inspector. The flaps were found fully extended, the rudder and elevator controls were jammed, and aileron continuity was established. The elevator trim was tab down. Fuel samples were taken from the left main tank. The fuel was a blue color and was free from visible contamination. A section of an engine connecting rod was found near the front of the aircraft. A hole was noted in the top of the left crankcase above the area of the No. 2 connecting rod. After removal of the engine from the aircraft, additional external damage was noted to include a second hole in the top aft area of the right crankcase. The left magneto was fractured and had been separated from the case. The engine was hand rotated and exhibited mechanical continuity with the following exceptions: the crankcase halves were separated and visually examined, which revealed internal impact damage on both halves; the main bearing surfaces appeared well lubricated and no fretting was noted on the main bearing saddles; the connecting rod caps and bolts corresponding to the No. 1 and 2 cylinders were found bent or broken; and one counterweight was found missing from the No. 2 long cheek. This blade was intact and the bushings were retained in the blade. Pieces of the fractured counterweight were recovered from the oil sump; however, one retaining pin, three retaining disks, and two snap rings were not located. All six cylinders had chrome bores which were free of visible scoring. The skirts of the No. 1, 2, and 3 cylinders exhibited internal impact damage. The extent of damage to the No. 1 cylinder prevented its removal. All pushrods, rocker arms, valves, and springs were intact. One base stud on the No. 1 cylinder was partially knocked out. All six pistons were intact, although No. 1 and 2 exhibited internal impact damage. The rings on No. 4 and 6 moved freely in their grooves. The lower ring on No. 2 was broken; however, the upper rings were intact and moved freely in their grooves. All six piston pins were intact. All crankshaft journals were found to be free from scoring or discoloration. The No. 1 and 2 connecting rod journals exhibited internal impact damage. The crankshaft gear was intact. The camshaft lobes and journals were free from scoring. Some internal impact damage was noted adjacent to the No. 1 and 2 cylinders. The No. 1 intake and exhaust and No. 2 intake lifters were fragmented and scarred. It was noted that the No. 1 and 2 connecting rods were broken at midspan and that both of their corresponding caps were fragmented. The rod nut and cotter pin from the No. 1 connecting rod was not located. The oil pump rotors were intact and the pump chamber walls were smooth and free from scoring. The driving rotor was coupled to the engine and residual oil was found in the pump. Both rotors of the scavenge pump were intact and the pump chamber walls were smooth and free from scoring. The driving rotor was coupled to the pressure pump and residual oil was found in the pump. The oil cooler was found to be intact and contained some residual oil. The right magneto was tested and produced a spark. The spark plugs were removed and all exhibited coloration and wear patterns consistent with the "normal" category of the Champion spark plug condition chart. The fuel pump contained residual fuel and pumped when the its shaft was rotated. The pump drive coupling was intact. The fuel metering unit fuel inlet screen was clean and the unit contained residual fuel. All three propeller blades were bent aft to varying degrees. One blade exhibited some chordwise scratching, while the second blade exhibited spanwise scratching, and the third blade exhibited a variety of scrapes and gouges. The propeller governor gasket screen was clean and free of foreign material. The governor oil pump contained residual oil and displaced oil when the drive shaft was rotated. The turbocharger was undamaged and its compressor impeller and turbine wheel were coupled and turned freely. The engine was transported to the Teledyne Continental factory for further examination. During the examination the torque and stretch of the connecting rod bolts were measured. The No. 3 top bolt broke loose at 25 ft/lbs. The lower bolt broke loose at 27 ft/lbs. The bolts were lubricated with engine oil and retorqued to the low torque value and then measured. The lower bolt was stretched .0001 inch longer than the "as found" condition. The top bolt stretched .0008 inch longer than the "as found" condition. The manufacturer's torque specification is 39.6 to 43.8 ft/lbs, with engine oil applied to the bolt threads. The bolts at the No. 4 connecting rod were stretched .0029 inch at the top bolt, and .003 inch at the lower bolt end. The stretch with engine oil applied to the threads at the low torque specification was .0037 inch on the top bolt and .004 inch on the lower bolt. The No. 3 top nut was damaged and no check was made at that end. The No. 3 bottom break-away torque was 35 ft/lbs. The No. 6 top break-away torque was 45 ft/lbs and the bottom was 40 ft/lbs. The manufacturer's findings are appended to this report. The engine was released to the owner's representative at the conclusive of the examination, and the Safety Board did not retain any components.
Fatigue failure of the No. 2 lower connecting rod bolt as a result of improper torque during the last engine overhaul.
Source: NTSB Aviation Accident Database
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