NYC07LA086

The flight instructor and student pilot were practicing stalls when the airplane experienced a sudden, total loss of engine power. Postaccident examination of the engine revealed that the left crankcase half idler gear shaft was dislodged from its respective mounting boss. The two idler gear shaft retaining bolts were broken. The idler gear that interconnected the crankshaft and camshaft remained on the idler shaft and was observed with a "U"-shaped fracture at the gear ring area that separated two full teeth. Optical examination of the gear fracture revealed fracture face markings, including arrest lines consistent of fatigue progression, which was estimated to cover more than 95 percent of the fracture surface. Both gear shaft retaining bolts were separated near their respective heads. The bolts displayed severe circumferential wear through the threaded shanks that removed the majority of the bolt diameters. High magnification viewing of the fractures in these areas on both bolts revealed features indicative of multiple origin fatigue propagating through the remaining cross sections. The lock plate was fractured in several locations and heavily distorted. The bolt holes in the lock plate were severely elongated and enlarged over their original diameter. While it was likely that loosening of the bolts precipitated the gear failure, no conclusive evidence was uncovered to confirm that scenario. The engine's most recent annual inspection was performed about 4 months prior to the accident. At that time, the engine had been operated for 1,226 hours since it was overhauled in 1985, and 639 hours since it was disassembled and reassembled after a propeller strike during 2001.

On March 25, 2007, about 0930 eastern daylight time, a Bellanca 7ECA, N53874, experienced a loss of engine power while maneuvering, and was substantially damaged during a forced landing, near Wawayanda, New York. The certificated flight instructor (CFI) and a student pilot sustained minor injuries. Visual meteorological conditions prevailed and no flight plan had been filed for the flight that originated at the Sussex Airport, Sussex, New Jersey. The local instructional flight was conducted under 14 Code of Federal Regulations Part 91.

According to a Federal Aviation Administration (FAA) inspector, the CFI was practicing stalls with the student pilot when the airplane experienced a sudden, total loss of engine power. The CFI subsequently performed a forced landing to a field; however, during the landing, the airplane nosed over and sustained substantial damage to the airframe and empennage.

The airplane was equipped with a Textron Lycoming O-235-C1 engine. Postaccident examination of the engine by an FAA inspector revealed that when the crankshaft was rotated, piston movement was noted; however, there was no evidence of camshaft rotation. The engine was retained for further examination.

The engine was subsequently disassembled at Textron Lycoming, Williamsport, Pennsylvania, under the supervision of an FAA inspector. The examination revealed that the left crankcase half idler gear shaft was dislodged from its respective mounting boss. The two idler gear shaft retaining bolts were broken. The separated head portion from each bolt was located in the oil sump. The idler gear that interconnected the crankshaft and camshaft remained on the idler shaft and was observed broken with several missing teeth. The crankshaft idler gear assembly, lock plate and both idler gear shaft retaining bolts were forwarded to the National Transportation Safety Board's Materials Laboratory, Washington, DC, for further examination.

According to the Safety Board metallurgist's factual report, the idler gear had a "U"-shaped fracture at the gear ring area that separated two full teeth. Optical examination of the gear fracture revealed fracture face markings, including arrest lines consistent of fatigue progression, which was estimated to cover more than 95 percent of the fracture surface. Both gear shaft retaining bolts were separated near their respective heads. The bolts displayed severe circumferential wear through the threaded shanks that removed the majority of the bolt diameters, creating an hourglass shape. High magnification viewing of the fractures in these areas on both bolts revealed features indicative of multiple origin fatigue propagating through the remaining cross sections. The lock plate was fractured in several locations and heavily distorted. The bolt holes in the lock plate were severely elongated and enlarged over their original 1/4 inch nominal diameter.

Review of maintenance records revealed that the airplane's most recent annual inspection was performed on December 1, 2006. At that time, the engine had been operated for 1,226 hours since it was overhauled on May 29, 1985, and 639 hours since it was disassembled and reassembled after a propeller strike during October 2001.