History of Flight
On April 29, 2013, at approximately 1215 Pacific daylight time, a Cessna 172M, registration N20800, made a forced landing in a vineyard near Lakeport, California, after a loss of engine power. The aircraft was registered to Air Ward, Inc., and operated by a commercial pilot under 14 CFR Part 91. The pilot was not injured, and the airplane sustained substantial damage to both wings and the horizontal stabilizer. The flight departed Lampson Field Airport, Lakeport, California, around 1200. Visual meteorological conditions prevailed, and no flight plan was filed.
The pilot reported a routine preflight check, engine run-up, and departure. During the initial climb to 4,000 feet, the engine began producing a rumbling sound, and its speed dropped to about 1,800 rpm. The pilot adjusted the fuel mixture and confirmed the fuel selector was set to both tanks, but the airplane could not maintain climb. He turned back toward Lampson Field; approximately three minutes after the initial anomaly, the engine lost all power. The pilot set best glide speed and performed a forced landing into a vineyard, where the aircraft struck a trellis.
Engine Examination
The engine was removed and examined. The oil sump contained about 5 quarts of black oil; the oil filter had no visible particles, and approximately one-quarter of the oil screen surface was covered in black debris. External examination showed that while the engine could be rotated by hand at the propeller hub, it required unusually high force. The valves and pistons of cylinders 1, 3, and 4 moved appropriately, and thumb compression was achieved for those cylinders after removing the lower spark plugs. No movement was observed in cylinder 2 components.
Partial disassembly revealed that piston number 2 had seized within the cylinder head. The connecting rod exhibited pink discoloration and remained attached to the crankshaft but had sheared at the small end, destroying the connection to the piston pin. The sump contained pulverized fragments of piston and rod material, connecting rod bearing, and connecting rod bolts. Both the number 1 piston rod and the crankshaft near the number 1 and 2 connecting rods were dry and showed discoloration consistent with excessive heat.
Oil Pump Examination
The engine oil pump, a meshed spur-gear type driven by the crankshaft, was removed from the accessory case. The pump housing exhibited a crack branching from the upper mounting hole through the support web at the oil pump input drive, extending beyond the web to the pump base. One tooth from the left impeller gear was fractured and missing; the right gear retained all teeth but had fractured at the root between two teeth, splaying the gear open so it no longer positively attached to the input drive shaft. Both gears were steel. The pump housing showed mushroom-like deformation at the interface with the input drive.
The oil pump was sent to the NTSB Materials Laboratory for metallurgical examination. Analysis indicated that the fracture surfaces on both gears had dull, tortuous features consistent with overstress failure. No evidence of fatigue or corrosion was found on the gear fracture surfaces. The inner surface of the pump housing displayed smearing and witness marks consistent with gear tooth contact, and the crack from the pump base to the input drive shaft web showed a witness mark along its entire length consistent with gear tooth contact.
Maintenance Records
According to maintenance logbooks, the engine was overhauled in 2004 at a total time of 7,061 flight hours (tachometer time 7,866 hours). The most recent annual inspection occurred on April 1, 2013, at a tachometer time of 10,160 hours.