History of Flight
On June 2, 2015, about 1955 Pacific daylight time, a Mooney M20K, registration N3567H, landed long after a total loss of engine power and subsequent forced landing at Fresno Chandler Executive Airport, Fresno, California. The airplane was operated by the pilot under 14 CFR Part 91. The private pilot, the sole occupant, was not injured. The airplane sustained substantial damage to both wings and the forward fuselage during the landing. The cross-country personal flight departed Shafter Airport-Minter Field, Shafter, California, about 1915, with a planned destination of Mc Clellan Airfield, Sacramento, California. Visual meteorological conditions prevailed, and a visual flight rules flight plan had been filed.
The pilot reported that the preflight inspection did not reveal any anomalies, and he added one quart of oil to the engine. About 30 minutes after takeoff, while cruising at an altitude of 8,500 ft mean sea level, he heard an explosion, and smoke and oil billowed from the cowl. The engine lost all power, and he initiated a descent into Fresno. He reached the airport environment with about 2,500 feet of altitude remaining, and attempted a landing on Runway 30R, which at that time was closed. The airplane landed on the overrun area and came to rest on a dirt verge after striking the perimeter fence.
Post accident examination revealed multiple perforations in the engine crankcase, with oil streaks along the underside of the airplane's fuselage.
Aircraft Information
The airplane was manufactured in 1980 and equipped with its original Continental Motors, six-cylinder, turbocharged engine, model number TSIO-360-GB(1), serial number 309443. At the time of the accident, the engine had accrued about 1,340 flight hours since new. The last oil change occurred 19.6 hours prior, on April 13, 2015, with the last inspection being an annual, completed on December 1, 2014, 46.6 hours prior to the accident. Maintenance records indicated that the engine had been disassembled and inspected in 1991, about 310 hours prior to the accident, after the airplane was involved in a ground collision while taxiing (see NTSB Accident Report: LAX91LA063B). A series of engine components were replaced following the inspection, including two connecting rods, twelve lifters, and one piston pin. The records did not specify for which cylinders the connecting rods and piston pin were replaced.
The airplane appeared to have gone through a period of inactivity from 1998 through to 2008. The first entry following that period stated, "Borescoped cylinders and portions of the crankcase, found surface corrosion on portions of the cylinders and hardware." The maintenance records did not document any subsequent repair in response to the corrosion, nor was there any evidence to suggest the engine had ever undergone a subsequent oil analysis or oil filter examination.
Examination Findings
The engine was removed from the airframe and examined at the facilities of Continental Motors in Mobile, Alabama under the oversight of the FAA and NTSB. Inspection revealed puncture holes in the crankcase above the number two and below the number three cylinders. No measurable oil remained in the engine. All spark plugs appeared undamaged, with the exception of both plugs for cylinder number one, which sustained mechanical damage displacing their electrodes.
The engine was disassembled, and cylinder head assemblies one, four, five, and six were removed. Skirt damage prevented the removal of cylinders two and three. The most significant internal damage was to the number one piston, which had separated from the connecting rod, was loose within the cylinder, and appeared to have been pulverized and fragmented to about 1/4 of its normal size. The connecting rod had fragmented into multiple pieces, and although the rod remained attached to the piston pin, it had been displaced to the pin's outer edge where it had seized. The piston-end of the rod had bent and separated at the beam, about 1 inch from the boss. All piston and rod assembly separation surfaces had been obliterated.
The connecting rods for cylinders two and three remained attached to their respective pistons, but their caps had both detached, resulting in separation from the crankshaft. The number four connecting rod was still attached to the crankshaft, but exhibited heat distress around the connecting rod cap. The remaining connecting rods for cylinder five and six appeared undamaged, with their caps intact at the crankshaft. The caps were removed, and the bearing and corresponding crankpin journal surfaces appeared undamaged and coated in oil.
The crankshaft number one, two, and four main journals exhibited normal operating appearance; with the number three journal displaying rotational scores and bluing.
The oil sump contained remnants of connecting rod, bearing, rod bolt, and aluminum material. The oil pump was disassembled, and scoring was observed on its rotational surfaces and the impellor gear tips. The oil filter was opened, and contained a sludge/metal mixture inside the canister, with fine sand-sized metal debris in the filter's paper element.
Continental Critical Service Bulletin CSB916-13 provides connecting rod inspection and replacement instructions for IO-360 series engines manufactured around the period of the accident engine. The service bulletin addressed replacement of connecting rods which were manufactured with a beam width of less than 0.625 inches. It required inspection and/or replacement of the affected rods at the next annual or 100-hour inspection, "Due to the potential for overstressed connecting rods associated with abnormal conditions or incidents." The engine did not fall within the serial number range applicable to the bulletin, and examination of the undamaged rods for cylinders four, five, and six revealed that all beam widths were 0.655, 0.658, and 0.657 inches respectively, and therefore greater than the minimum required. Furthermore, the maintenance records for the connecting rod replacement in 1991 indicated that the part numbers of the two replaced rods were of the correct type required by the service bulletin.