Brandon, MS, USA
N9708M
Mooney M20F
The pilot stated that he performed a preflight inspection of the airplane and noted the oil capacity was full (8 quarts). Approximately 2 hours into the flight while flying at 10,500 feet, the engine began running rough. He advised air traffic control (ATC), and attempts to correct the rough running engine were unsuccessful. The flight continued and shortly afterwards, the engine developed a severe roughness and he then heard a bang with smoke entering the cockpit. He declared "mayday" with ATC, and requested vectors to the nearest airport. Unable to land there, he executed a forced landing on a nearby highway and collided with a vehicle during the landing roll-out. The No. 3 cylinder was found separated from the crankcase, and all cylinder studs and/or thru-bolts exhibited various forms of fatigue. The No. 3 cylinder connecting rod bolts which were fractured exhibited evidence of either bending or shear overstress. The No. 2 cylinder connecting rod bearing was found welded to the crankpin, and a piece of aluminum lined bearing material was found inside the oil passage of the No. 2 cylinder crankpin journal. Fretting was noted at the No. 3 cylinder contact area, and also at the split-line surface of the right crankcase half at the main bearing locations. The fretting was the greatest at the cylinder contact area between studs Nos. 1 and 2, and also at the split line surface on the right crankcase half at the No. 3 main bearing location. The engine had accumulated 1,390 hours since major overhaul and approximately 873 hours since the No. 3 cylinder was removed and reinstalled.
On September 5, 2004, about 1432 central daylight time, a Mooney M20F, N9708M, registered to a private individual, experienced a total loss of engine power and collided with a vehicle during a forced landing on a highway near Brandon, Mississippi. Visual meteorological conditions prevailed at the time and a visual flight rules (VFR) flight plan was filed for the 14 CFR Part 91 personal flight from Dekalb-Peachtree Airport, Atlanta, Georgia, to Shreveport Downtown Airport, Shreveport, Louisiana. The airplane was substantially damaged and there were no injuries to the private-rated pilot and two passengers in the airplane, or to the driver of the vehicle. The flight originated about 1310, from Dekalb-Peachtree Airport. The pilot stated that he performed a preflight inspection of the airplane and noted the oil capacity was full (8 quarts). The flight departed and approximately 2 hours into the flight while flying at 10,500 feet, the engine began running rough. He advised air traffic control (ATC) and attempts to correct the rough running engine were unsuccessful. The flight continued and shortly afterwards, the engine developed a severe roughness and he then heard a bang with smoke entering the cockpit. He declared "mayday" with air traffic control and requested vectors to the nearest airport. Recognizing that he would be unable to reach the Jackson International Airport, he advised ATC of his intention of landing on a nearby highway. After landing on the highway during the landing roll, the left wing of the airplane collided with the left rear portion of a truck. He and his passengers exited the airplane which was later taken to a fixed-base operator (FBO) located on the Jackson International Airport. Postaccident examination of the engine by an FAA airworthiness inspector revealed the No. 3 cylinder was separated from the engine crankcase; all cylinder studs were fractured. The No. 3 cylinder connecting rod cap was found at the accident site; the connecting rod bearing was missing. Two fractured 7/16 inch cylinder hold down studs with nuts attached, two fractured 5/16 inch cylinder hold down studs with nuts attached, one partial connecting rod bolt with nut, and one hydraulic lifter were found on the bottom engine cowling. Disassembly of the engine revealed that the No. 2 piston and connecting rod exhibited extreme heat discoloration. The No. 2 connecting rod bearing was "welded" to the crankpin journal, and a foreign object was noted in the oil passage at the journal; the foreign object was retained for further examination. Examination of the oil pump revealed the gears were not failed; metal particles were present in the oil pump housing. The right crankcase half which contains cylinder Nos. 1 and 3 was retained for further examination by the NTSB Materials Laboratory, located in Washington D.C. NTSB examination of the right crankcase half revealed cylinder hold down studs identified for the investigation as Nos. 1 and 8 which were the aft two cylinder hold down studs exhibited fracture features consistent with low-stress, long-term fatigue propagation. The fracture features of studs identified as Nos. 2, 3, 6, and 7, and thru-bolt No. 5 were consistent with rapid, high-stress fatigue propagation. The fracture features of thru-bolt identified as No. 4 was consistent with reverse bending fatigue. Examination of the No. 3 cylinder connecting rod bolt remaining inside the separated connecting rod cap revealed fracture features consistent with shear overstress, while the section of connecting rod bolt which was found at the bottom of the engine cowling exhibited fracture features consistent with bending overstress. The two available connecting rod bolt sections did not appear to mate with each other, and the remaining fracture halves of both bolts were not recovered. The cylinder attachment area for the No. 3 cylinder exhibited a large circular impression which was consistent with impact damage from the piston contacting the crankcase. Some fretting, which appears as a brown stain, was found around most of the contact surface of the No. 3 cylinder contact area, with the most significant fretting between studs Nos. 1 and 2. Additionally, wear lips were observed mostly in the vicinity of the large diameter studs/bolts, with the damage being more severe adjacent to thru-bolts Nos. 4 and 5. Some fretting was also noted at the split-line surface of the right crankcase half at the No. 3 main bearing location, while "...minimal fretting..." was noted at the split-line surface of the right crankcase half at the Nos. 1, 2, and 4 main bearing locations. The object retrieved from the oil passage of the No. 2 crankpin journal was examined and found to be consistent with aluminum lined bearing material. Review of the maintenance records revealed the engine was overhauled on June 9, 1978; there was no entry in the airframe logbook indicating engine installation following overhaul. On July 22, 1984, the Nos. 2 and 3 cylinders were removed and an oversized thru-bolt was installed at the "center upper thru-bolt" location. The engine had accumulated 1,390 hours (by tachometer time) since overhaul at the time of the failure, and 873.3 hours since the No. 3 cylinder was removed and reinstalled. The airplane minus the retained components were released to Shaen Phillips of U.S. Aviation Underwriters, Inc., on October 21, 2004. The retained components were also released to Shaen Phillips on May 5, 2005.
A loss of engine power due to the fatigue failure of all studs and/or thru-bolts of the No. 3 cylinder for undetermined reasons causing separation of the cylinder. Contributing to the accident was the unsuitable terrain encountered by the pilot.
Source: NTSB Aviation Accident Database
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