NTSB Factual Report

On January 9, 2009, at 2210 Pacific standard time, a Cessna R172K, N758FN, sustained substantial damage during a precautionary off-airport landing near Fremont, California, shortly after departure from the Palo Alto Airport of Santa Clara County, Palo Alto, California. The commercial pilot, the sole occupant of the airplane, was not injured. The airplane was owned by the pilot, and operated as a visual flight rules (VFR) personal flight under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91. Night visual meteorological conditions prevailed and no flight plan was filed for the local flight.

In a written report to the National Transportation Safety Board, the pilot reported that after takeoff, during a left turn, he heard a "sudden" change in the engine sound followed by a loss of power. He stated "I looked at the oil temperature [gauge] and noticed it on the very low (left side) of the gauge." The pilot reported that he increased and decreased the throttle with "very little" response from the engine and elected to make a precautionary landing onto a nearby levy. During the landing roll on the levy, the airplane veered to the right, exited the levy and nosed over in a bog. Both wings sustained substantial damage.

The airplane was recovered from the accident site to a storage facility in Pleasant Grove, California. During the postaccident airframe and engine examination, the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) and a representative from the Federal Aviation Administration (FAA) started the airplane's engine. The engine ran at idle for approximately one minute; oil pressure and tachometer gauge readings were nil, and the engine run was discontinued.

The accessory gear cover was removed and the gear assembly was examined. The examination revealed that the oil pump/tachometer drive gear (part number 653236) separated from the base of its respective drive shaft. The drive gear and shaft were removed and shipped to Teledyne Continental Motors, Inc, for further evaluation.

The examination was completed at Teledyne Continental Motors (TCM), Materials and Processes Laboratory, Mobile, Alabama. According to the examination report, completed by personnel from TCM, the oil pump/tachometer drive gear failed at the intersection of the shaft and gear. Scanning electron microscope (SEM) images of the fracture showed raised and flattened areas typical of contact damage during cyclic loading. The reason for the fracture was not determined.

Review of the engine maintenance logbook revealed that an annual inspection was completed on July 15, 2008, at an engine total time of 4,904 hours; 1,864 hours since major overhaul.

NTSB Probable Cause

The partial loss of engine power during takeoff due to an oil pump/tachometer drive gear failure for undetermined reasons.