MARYSVILLE, CA, USA
N4932B
Beech J35
The pilot radioed that the aircraft's engine was failing and he was altering his course to land at the nearest airport. While on left base leg for landing, the cowling flew open, oil filled the windshield, and the engine ceased delivering power. The aircraft impacted a tree and came to rest in a city park. At the scene, the No. 6 engine cylinder was separated from the crankcase and engine components associated with that cylinder were found over a 40-foot radius around the aircraft. The engine crankcase where the No. 6 cylinder attached was broken away at the 12 o'clock position; the upper forward, upper rear, and lower rear mounting studs were broken; and the lower forward stud and the two lower center studs were present. The skirt of the No. 6 cylinder exhibited a pattern of longitudinal striations where it mated into the crankcase opening. At the lower left of the cylinder mount location was a small ledge of material, which approximated the shape of the circumference of the cylinder base flange. Opposite this location, on the upper right of the cylinder mounting location, was a brightly polished wear area. The engine received a top overhaul 7 months, 41.8 hours prior to the accident. Breakaway torque was measured on the remaining cylinder base nuts and found to range between 25 and 40 foot-pounds; the specification torque values are between 40.8 and 42.5.
HISTORY OF FLIGHT On August 17, 1999, at 1131 hours Pacific daylight time, a Beech J35, N4932B, was destroyed when the aircraft impacted a tree and terrain short of the runway during an emergency landing approach at the Yuba County Airport, Marysville, California. The commercial pilot and a passenger, who held a private certificate, were seriously injured. Visual meteorological conditions prevailed for the personal flight, operated by the owner/pilot under the provisions of 14 CFR Part 91. The flight departed from the Marin (private) airport at San Rafael about 1045, and was destined for a private ranch airport near Caldwell, Idaho. No flight plan was filed. When approximately 7 miles northeast of Marysville, the pilot radioed Sacramento Approach Control at 1116 that he was at 8,000 feet (msl) over Beale Air Force Base and was "having rough engine problems." He stated that he intended to land at Marysville. At 1119, the controller identified the aircraft on radar over Beale and the pilot reported Marysville in sight. The pilot said he intended to maintain his present altitude until over the field (Marysville) before making any further throttle position changes. At 1121, the pilot reported, "from the indications on the egp [EGT] it looks like I've lost half the engine." At 1124, the pilot reported he was over the airport descending at 500 feet per minute and still experiencing the rough engine. At 1128:14, the pilot radioed, "the cowling came off and I got oil coming through the windshield here." At 1128:54, the controller advised the pilot he was 2 miles north of the airport. At 1129:28, the pilot advised he was lowering the aircraft's landing gear. At 1130:15, the controller advised the pilot he observed him on radar on base leg 1.5 miles north of the airport and asked if the pilot still saw the airport. The pilot replied "three two bravo still has." The final communication with the aircraft was at 1130:31 regarding possible traffic, which the pilot acknowledged at 1130:43. The passenger reported that when they were on left base leg for runway 14, the cowling flew open, oil filled the windshield, and the engine ceased delivering power. The aircraft impacted a tree approximately 75 feet above ground level, and then came to rest in the West Linda Park about 0.75-mile northwest of the airport. At the scene, the No. 6 engine cylinder was separated from the crankcase, and engine components associated with that cylinder were found over a 40-foot radius around the aircraft. According to paramedic personnel, the male occupant was seated in the left front seat and the female occupant was seated in the right front seat. AIRCRAFT INFORMATION According to the engine logbook for the aircraft, the engine received a top overhaul on January 29, 1999 at engine tachometer time 87.6 hours. At the accident site the tachometer read 129.4 hours. During the top overhaul, six factory new Teledyne Continental Motors cylinder assemblies were installed. WRECKAGE AND IMPACT INFORMATION The accident location was in an area of level grass covered terrain in the West Linda Park in the city of Marysville. From the accident location, the threshold of runway 14 at the Yuba County Airport is approximately 0.75 miles south. The latitude and longitude were 39 degrees 06.92 minutes north and 121 degrees 34.78 minutes west (GPS), respectively. The elevation was approximately 60 feet msl. There was no fire and all of the aircraft was present at the site except the No. 6 piston and some parts associated with the No. 6 cylinder installation on the engine. There was a debris field oriented approximately north south, which was about 120 feet long. At the north end of the debris path were several tree branches, typically 2 inches in diameter lying on the ground. An adjacent tree showed evidence of fresh disturbance approximately 75 feet above its base. At the opposite (south) end of the debris path was the main aircraft wreckage, which was aligned with the nose pointing north. About 35 feet north of the aircraft was an area of freshly disturbed dirt approximately 4 feet in diameter and 10 inches deep. Several pieces of window Plexiglas, typically 12 inches in size, most coated with a brownish liquid resembling oil, were located near the hole. Pieces of green glass were located about 15 feet east of the area of disturbed dirt. About 25 feet north of the aircraft was an engine connecting rod, minus the cap portion, and a piston wrist pin. About 30 feet west and southwest of the aircraft were two valve pushrods and pushrod housings. The aircraft was upright and aligned with the nose pointing north. There was a crush plane oriented approximately 60 degrees from the longitudinal axis from the nose toward the right wingtip. The nose of the aircraft and engine were displaced about 60 degrees to the left and the engine was inverted about 135 degrees counter-clockwise. The right wing was destroyed outboard of the midspan and the main landing gear was extended. The inboard leading edge of the right wing exhibited crushing damage. The cabin area of the fuselage retained its shape although the Plexiglas windows were absent. The skin of the aft fuselage was separated on the left side aft of the cabin and exhibited compression damage on the right side opposite. The empennage stabilizer surfaces and two radio antennas on the top of the fuselage were coated with a brown liquid resembling engine oil. The brown liquid was streaked aft from the leading edge toward the trailing edge. The left wing exhibited two impact marks in the outboard leading edge, and the main landing gear was collapsed. One blade of the 3-bladed propeller was bent smoothly aft over its span about 60 degrees. The other two blades exhibited minor damage. None of the blades exhibited any chordwise striations, leading edge damage, or torsional bending. The flight controls were continuous. The four fuel tanks contained a clear blue liquid that looked and smelled like aviation fuel. The engine fuel selector was positioned on the right main fuel tank. The right main tank was ruptured and rescue personnel reported that fuel was observed draining from the tank onto the ground after the accident. The No. 6 cylinder was located on the ground beneath the engine and remained connected to the exhaust manifold. The internal bore of the cylinder was visually undamaged, as were the intake and exhaust valves. The flange at the base of the cylinder was bent at the 6 o'clock position approximately 15 degrees. The cylinder skirt was broken at the 12 o'clock position. The exterior of the cylinder exhibited local damage to cooling fins. Two hydraulic valve lifters were also on the ground beneath the engine. Two valve pushrods and two pushrod housing tubes (four separate parts) were found approximately 25 feet southwest of the aircraft. The engine crankcase where the No. 6 cylinder attached was broken away at the 12 o'clock position over an area about 4 inches diameter between the cylinder mounting base and the case backbone. The top two cylinder mounting studs were not located nor was the broken material from the crankcase. The upper forward, upper rear, and lower rear mounting studs were broken. The lower forward stud and the two lower center studs were present. None of the cylinder base nuts were present. The No. 6 connecting rod and piston wrist pin were found 25 feet in front of the aircraft. The connecting rod exhibited scraping damage on one side along its length. One cap bolt was missing and the other was broken and was lodged in the hole of the rod. The piston wrist pin was undamaged except for a 0.2-inch dent in each end cap. The connecting rod bearings and rod cap were located inside the oil sump of the engine. One bearing half and the rod cap were damaged while the other bearing half was visibly undamaged. The No. 6 piston was not located. The engine oil screen contained two small flecks of non-magnetic metal material. The engine fuel lines forward of the firewall contained a blue liquid resembling fuel. The spark plug electrodes were clean and undamaged but were wet with a fresh coating of a liquid resembling engine oil. The engine was disassembled and further examined by the Safety Board investigator at the facilities of Teledyne Continental Engines in Mobile, Alabama, on October 26, 1999. The engine had external damage to ignition wires, cooling baffle, and cooling fins. The core of the engine was intact except for the No. 6 cylinder assembly, which was separate. The intake manifold front cross tube was severed near the No. 6 cylinder and the intake "Y" tubes at the rear of the engine were separated from the engine. The fuel injection pump, control unit, and air valve were intact although the air valve inlet was blocked by deformed inlet box structure. The fuel distribution manifold (spider) had impact damage but was intact except for the attachment to the No. 6 nozzle. The injectors were free of debris. The air inlet path was clear of foreign debris. The exhaust manifold was intact on the right side up to the muffler connection and was broken from the cylinders at the base flanges on the left side. On cylinders No. 1 through 5, some cylinder base nuts had white torque seal applied, some case trough bolts had blue torque seal applied, and some top and all lower cylinder base nuts had no torque seal applied. The engine vacuum pump, starter, and alternator rotated freely by hand. The propeller governor turned by hand and pumped oil and the base screen was clear. The magnetos sparked and the spark plug electrodes were round and free of fouling. The engine sump was removed and contained segments of material resembling piston rings and approximately 10 pieces of brittle, non-magnetic metal material typically 1/2 inch is size. The pieces were plated with a flat black finish. Also found were two bolts identified by the Teledyne Continental party representative as connecting rod bolts. One bolt was symmetrically necked down and exhibited shear lips at the separation. The nut end of this bolt was not located. The other bolt exhibited necking down and shear lips accompanied by bending at the separation. The necked end of this bolt visually mated to the nut end of the bolt trapped in the connecting rod. The accessory case was removed and the accessory gears were intact and visually undamaged. The oil pump and oil screen had small flecks of shiny, non-magnetic metal material, however, the bore of the oil pump was visually un-scored. Breakaway torque for the cylinder base nuts was measured when removing the cylinders. The breakaway torque for the crankcase through bolt nuts was approximately 60 foot-pounds. The breakaway torque for the crankcase stud nuts varied between 25 and 40 foot-pounds. According to the Teledyne Continental party representative, the specified torque for the through bolts nuts is 57.5 to 59.1 foot-pounds and case stud nuts is 40.8 to 42.5 foot-pounds. The pistons and cylinder assemblies for the Nos. 1 through 5 cylinders were visually undamaged except for an area on the skirt of the No. 5 piston and cylinder base which had impact damage in the area opposite the No. 6 cylinder connecting rod journal. The combustion chambers exhibited modest combustion deposits, the cylinder walls were shiny and unscored, the pistons and piston rings were intact, and the valve train was visually undamaged except for the No. 6 cylinder pushrods. The crankcase halves were separated and exhibited a 1/2 inch gouge in the wall of the case at the base of the No. 5 cylinder opposite the No. 6 crankshaft throw and extensive damage to the opposite case half at the mounting pad of the No. 6 cylinder. The crankshaft was visibly undamaged and the journals were shiny and exhibited a smooth, mirror-like appearance. The crankshaft bearings exhibited a uniform dull gray appearance and were undamaged except for the connecting rod journal bearings from the No. 6 cylinder. The camshaft was visibly undamaged. The piston of the No. 6 cylinder was absent. The combustion chamber of the No. 6 cylinder had shiny walls and modest deposits in the dome. There were no impact marks in the combustion chamber. The valve train was visually undamaged although one pushrod and pushrod housing exhibited approximately a 10-degree bend over the length of the rod. The flange at the base of the cylinder was bent approximately 10 degrees toward the head of the cylinder over approximately a 45-degree sector angle at the 6 o'clock position. A mark at the center of the bent flange corresponded in width to the width of the connecting rod at the piston pin end. The skirt of the No. 6 cylinder exhibited a pattern of longitudinal striations where it mated into the crankcase opening. The Nos. 1, 2, 3, and 4 cylinder skirts did not exhibit any of this type pattern of marks, and the No. 5 cylinder exhibited a modest amount of similar marking. The top of the No. 6 connecting rod was identified by the position number stamped on the rod and the rod cap. The rod cap was partially flattened. The nut end of one rod bolt was trapped in the lower rod hole. Two rod bolt head ends were located in the engine sump. One, which appeared to mate to the (bottom) trapped nut end, exhibited necking and downward bending at the separation, while the other (upper) bolt exhibited necking at the separation but no apparent bending. The shaft of the connecting rod exhibited lengthwise scraping marks along the length of the lower flange bottom surface, which visually matched marks in the crankcase cylinder opening. The No. 6 cylinder mounting location on the crankcase, as viewed from the side of the engine looking inboard, was missing a triangular shaped piece of the case, approximately 3 inches on each side, and centered over the mounting location at the 12 o'clock position. The upper 2 cylinder mounting studs are part of this piece. The two studs and the material from the broken triangular shaped section of the crankcase were not located. The perimeter of the triangular broken section of the crankcase, and the backbone of the case in the area where the two sides of the triangle converged, exhibited upward bending. The upper front through bolt and upper rear stud were broken in the threaded area. Below each was a gouge on the crankcase, the shape of which approximated the radius of the piston skirt. At the lower left of the cylinder mount location was a small ledge of material extending over about 3 inches that could be felt with the fingernail which approximated the shape of the circumference of the cylinder base flange. Opposite this location, on the upper right of the cylinder mounting location and on the inside circumference of the crankcase opening was a brightly polished wear area. The lower right cylinder mount stud was broken in the threaded area. The lower left mounting through bolt and the two bottom center mounting studs were intact. Examination of this bolt and two studs under a magnifying glass showed that the thread peaks were worn flat over a portion of the circumference but that the threads in other areas of the circumference were visibly undamaged. ADDITIONAL INFORMATION The aircraft wreckage was released to Mr. Jerry Wallace, adjuster for Great American Insurance Company, on November 10, 1999.
A loss of engine power due to improperly torque cylinder base nuts by maintenance personnel during a top overhaul.
Source: NTSB Aviation Accident Database
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