Elma, WA, USA
N6422U
MOONEY M20C
The airplane was returning to its home airport following an aerial observation mission. A witness reported that the airplane was making a clattering noise as it flew over her home and commented that it sounded as if it was running out of oil. The witness estimated the airplane to be 100-150 feet above ground level. A second witness reported that the airplane descended into the tree canopy and collided with power transmission lines. Post accident examination of the engine revealed extensive thermal and impact related damage. The main bearings exhibited erosion and copper was visible. A large hole was observed in the engine crankcase above the number four cylinder bay and mechanical damage was observed to the area surrounding the cylinder. The number four connecting rod remained attached to the piston; however, the connecting rod was separated from the crankshaft at the base of the yoke. Fragments of the associated connecting rod cap and corresponding bolt were found within the engine oil sump; only residual oil (less than one quart) was observed within the sump along with debris, which was consistent with main bearing material and had obscured the oil pickup screen. Two fractures were found on the connecting rod near the end of the rod. The first noted was a fatigue fracture that initiated at the crankshaft end connecting rod journal surface just below the boss for the connecting rod bolt/nut. On the opposite side of the connecting rod, in a similar location, a second fracture was identified. The fracture was the result of mechanical overload and initiated at the connecting rod journal surface. The connecting rod bolt fracture surface exhibit features consistent with mechanical overload. The lack of engine oil found in the crankcase is believed to have contributed to the main bearing erosion; however, it was not determined if the bearing erosion was the initiating event.
HISTORY OF FLIGHT On July 22, 2009, at 1447 Pacific daylight time, a Mooney M20C, N6422U, was destroyed following a collision with terrain and post crash fire approximately 3 miles northwest of Elma, Washington. The commercial pilot, the sole occupant of the airplane, was killed. The airplane was registered to the pilot, and was operated as a visual flight rules (VFR) private fire patrol flight under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The flight departed Olympia, Washington, at 1417; no flight plan was filed. Visual meteorological conditions prevailed at Olympia, Washington and the accident location. A witness observed the accident airplane flying over her home and estimated it was 100 to 150 feet above ground level (agl). The witness stated the airplane was making a distinctive "clattering noise" and reported that it sounded as if it was running out of oil. She stated that the airplane turned right towards Elma and eventually lost sight of the aircraft. A second witness observed the airplane enter the tree canopy and then collide with power transmission lines. The witness stated the airplane was traveling 60-70 miles per hour and "exploded" when it impacted terrain. PERSONNEL INFORMATION The pilot, age 77, held a commercial pilot certificate with an airplane single-engine land rating. The pilot's most recent second-class medical certificate was issued on April 16, 2009, with no limitations or waivers. On the pilot's application for medical certificate, dated April 16, 2009, the pilot indicated that his total aeronautical experience consisted of about 6,000 hours, of which 300 were accrued during the previous 6 months. No personal flight time records were located for the pilot. AIRCRAFT INFORMATION The 4-place, low-wing, single engine airplane (serial number 2169) was manufactured in 1962 and powered by a four-cylinder Lycoming O-360 engine rated at 180 horsepower. A review of the airplane's maintenance records showed that an annual inspection of the airframe and engine was completed on May 1, 2009. The engine logbook showed that at the time of inspection the engine had accumulated approximately 2,606 total hours, and 1,050.6 hours since major overhaul. The airframe total time at inspection was 3,261 hours. Engine logbook records showed that on September 5, 1980, the engine "received [a] major overhaul in accordance with the manufacturer's overhaul manual 60294-7." Detailed overhaul/build records for the engine were not located. Damage precluded determining the current tachometer and Hobbs hour-meter readings. MEDICAL AND PATHOLOGICAL INFORMATION The FAA's Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed toxicological testing on the pilot. The test results were negative for ethanol and controlled substances. See attached toxicology report for specific parameters and results. An autopsy was performed under the guidance of the Grays Harbor County Coroner, Aberdeen, Washington, on July 23, 2009. The postmortem report attributed the cause of death to "multiple blunt trauma injuries." TESTS AND RESEARCH The wreckage was recovered and transported to a storage facility in Maple Valley, Washington. Following recovery, the engine was examined and disassembled under the supervision of Safety Board investigators and inspectors from the FAA. The following observations were noted during the August 19, 2009, examination. The engine case, cylinders and accessories exhibited extensive thermal and impact related damage. The engine had separated from the airframe; however, the engine mounts remained intact and attached to the engine. The propeller assembly remained attached to the crankshaft and nominal damage was noted. All four cylinders remained attached to the engine crankcase and the associated rocker covers were in place. The oil filler cap was found secure to the oil filler tube and the oil sump was intact. All of the engine fuel and oil lines were thermally damaged. The oil cooler was intact and exhibited thermal damage. A large hole was observed in the engine crankcase above the number four cylinder bay and mechanical damage was observed to the area surrounding the cylinder. The number four cylinder was removed and examined. The intake and exhaust rocker arms were intact and exhibited thermal damage. Extensive mechanical and thermal damage was noted to the piston and associated cylinder. The number four connecting rod remained attached to the piston; however, the connecting rod was separated from the crankshaft at the base of the yoke. Fragments of the associated connecting rod cap, bolt and corresponding nut were found within the engine oil sump. The number one and two main bearings were intact. The number two bearing was worn, exposing the copper layer. The number three main bearing was observed slightly shifted in a clockwise direction (aft looking forward) and partially obscured the oil passage port. The bearing exhibited thermal discoloration and wear, exposing the copper layer. The number four main bearings exhibited thermal damage and wear, exposing the copper layer. Residual oil (less than one quart) was observed within the sump along with debris. The debris was consistent with bearing, piston, crankcase, and connecting rod material. The oil pickup screen was partially obstructed by the debris. The oil sump was intact and undamaged. The number 4 connecting rod and debris from the oil sump was forwarded to the NTSB Materials Laboratory, Washington, DC. Examination of the connecting rod by an NTSB metallurgist revealed two fractures near the end of the connecting rod. The metallurgist noted that a fatigue fracture initiated at the crankshaft end connecting rod journal surface, just below the boss for the connecting rod bolt/nut. On the opposing side of the connecting rod, in a similar location, a second fracture was identified. The metallurgist reported that this fracture was the result of mechanical overload, and initiated at the connecting rod journal surface. The recovered section of the connecting rod bolt was examined. The metallurgist reported that about 80 percent of the fracture face was damaged. The remaining area of the fracture surface exhibit features consistent with mechanical overload. Additional information pertaining to the engine and metallurgical examinations is contained within the public docket for this accident.
A total loss of engine power during cruise flight due to the fatigue failure of the number 4 cylinder connecting rod.
Source: NTSB Aviation Accident Database
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