NTSB Factual Report

On July 5, 2004, approximately 1115 mountain daylight time, a Cessna T210N, N5408A, registered to and operated by PinesAir, Inc., of Pine Bluffs, Wyoming, and piloted by a private pilot, was substantially damaged when it collided with terrain during an off-airport forced landing about 8 miles west of Spanish Fork, Utah. The pilot and three passengers were not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the personal cross-country flight being conducted under Title 14 CFR Part 91. The flight originated at Provo, Utah, approximately 1100, and was en route to Kimball, Nebraska.

According to the pilot, he departed runway 13, turned right onto the crosswind leg, departed the traffic pattern to the southwest, and climbed towards West Mountain. Shortly thereafter, the LOW VOLTAGE warning light illuminated. Cycling the avionics and master switches several times failed to extinguish the annunciator light. He decided to return to Provo. En route, the engine sounds "changed" and the engine began to lose power. Boost pump and magneto checks were made with negative results. Due to the loss of altitude, the pilot made an intentional wheels up landing in a field. The airplane slid 670 feet before coming to a halt.

The airplane was later recovered and examined. The alternator pulley shaft was broken and the pulley and broken shaft lay atop the engine. Borescoping the cylinders revealed crescent-shaped indentations on all six piston heads. Drive train continuity was established, but the camshaft would not turn.

The engine, a Continental TSIO-520-R (s/n 511784), was removed from the airframe and shipped to Teledyne Continental Motors (TCM) in Mobile, Alabama, where, on February 17, 2005, it was disassembled and examined. The magneto drive gear and axle were pushed up, and the right magneto coupling was fractured. The crankcase was also fractured in an upward direction at the axle seat. Pieces of gear teeth and magneto coupling were found in the oil sump. When bench tested, the left magneto fired consistently in the 500-3,000 rpm range; the right magneto would not fire. Disassembly revealed excessive distributor gear bushing wear. Reddish-brown filings, similar to bushing material, coated the inside of the magneto case. When the alternator drive assembly was removed, it was discovered that 9 of 15 gear teeth were stripped. Metallurgical examination by microscope revealed the shaft failed in torsional overload, followed by crushing and smearing of the gear teeth.

The crankshaft and the number 2 main bearings had shifted forward approximately 1/8-inch. Fretting was noted on all the crankcase through-bolt holes. An adhesive residue covered the inside seam faces and through-bolt holes. The number 4 main bearing thrust washer was fractured with rotational scoring of the crankshaft. Both the crankshaft and camshaft had numerous fractured teeth that were crushed and ground. Crescent-shaped witness marks, consistent with intake and exhaust valve strikes, were noted on all six piston heads. The camshaft lobes and all lifters bore irregular impact signatures.

The airplane maintenance records were examined. The engine was last overhauled on January 22, 1993, at a tachometer time of 3,692.0 hours. The logbook entry bore the following statement: "This engine has been overhauled to new factory fits and limits, and has been assembled in accordance with note 5 of TCM SB (Service Bulletin) M89-13, extending the TBO (time between overhaul) to 1,600 hours." On April 25, 2000, at a tachometer time of 4,700.0 hours (1,008.0 hours since major overhaul), 6 new "classic cast" cylinder assemblies were installed along with new pistons, rings, and piston pins. At the time of the accident, the tachometer read 5,435.0 hours. The engine had operated 1,743.0 hours since major overhaul (143.0 hours beyond recommended TBO), and 735.0 hours since the new cylinders and pistons were installed.

NTSB Probable Cause

the improper reassembly of the engine following major overhaul (application of Permatex over entire crankcase surfaces). Contributing factors included the number 2 main bearing and crankshaft shifting forward, causing the alternator drive shaft and other accessory gears to fail, which disabled the camshaft.