N739SU

HISTORY OF FLIGHT

On December 7, 2003, at 1600 Pacific standard time, a Cessna 172N, N739SU, lost engine power and collided with the ground while executing a forced landing 8 miles west of Snelling, California. The American School of Aviation operated the airplane under the provisions of 14 CFR Part 91. The student pilot and a designated examiner were not injured, and the airplane was substantially damaged. Visual meteorological conditions prevailed, and no flight plan had been filed. The local area instructional flight originated at Castle Airport, Atwater, California, at 1545.

The designated examiner reported to the Safety Board investigator that about 5 minutes into the private pilot check flight the vacuum instruments failed, then 5 minutes later, at 3,000 feet, the engine made a loud noise and black smoke entered the cockpit. The smoke seemed to originate from the engine. The engine lost power and was not responding to throttle adjustments. The designated examiner took the airplane's controls and selected a green field into which to perform a forced landing. During the landing touchdown the nose wheel caught the ground, and the airplane nosed over on to its back. The aircrew safely egressed the airplane uninjured.

TESTS & RESEARCH

Under the supervision of the Safety Board Investigator, Cessna, and Lycoming technical representatives examined the engine. The four cylinder engine had a 4 inch lateral hole in the top of the engine case, above the number 4 cylinder, between the push rod tubes. The engine crankshaft was rotated by hand and it was noted that the oil pump drive shaft did not rotate with the rest of the engine accessories. The engine was then disassembled. The number 3 cylinder connecting rod was fractured at the I-beam mid section and the rod bearing inserts were discolored, deformed, and in pieces. The number 4 cylinder connecting rod I-beam was fractured just above the crankshaft and the bearing inserts were deformed. The gear type oil pump was disassembled. The oil pump woodruff key was observed sheared in half along the interface between the drive shaft and the accessory drive gear.

The vacuum pump rotated freely and the flexible drive coupler was intact.

Examination of the engine and aircraft log books documented that the annual/100 hour inspection was completed on November 1, 2003, at a engine total time of 1721.3 hours.

The Lycoming O-360-H series overhaul manual shows that the engine driven oil pump drive shaft also drives the instrument vacuum pump.