On January 19, 2000, a Mooney M20K (registration N1157G) was involved in an aviation accident near Tyler, TX. Investigators recorded the probable cause as: Fatigue fracture of the crankshaft drive gear teeth resulting in loss of engine power. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A pilot reported total engine power loss during cruise between 1,500 and 2,000 feet agl. Forced landing resulted in contact with a fence post. Postaccident examination revealed a fractured crankshaft drive gear with fatigue areas at three separated teeth.
Event Description
The pilot reported that the engine experienced a total loss of power while in cruise flight at an altitude between 1,500 feet and 2,000 feet above ground level. He subsequently executed a forced landing, during which the airplane contacted a fence post.
Postaccident Examination
During the postaccident examination of the engine, the crankshaft drive gear was observed to be fractured. Three consecutive gear teeth of the crankshaft drive gear had separated, and two of the separated teeth were recovered.
Metallurgical Findings
The crankshaft drive gear and the separated gear teeth were examined at the NTSB Materials Laboratory. Three areas of fatigue were observed. Each fatigue area originated at the relief radius at the root of one of the three separated teeth. No tooling marks or gouge marks were observed near the fracture surface or on the remainder of the crankshaft gear's teeth. The outermost nitrided layer of the crankshaft drive gear appeared smooth and no cracks were noted. Additionally, machining marks through the entire crankshaft drive gear appeared consistent.
Probable cause
Fatigue fracture of the crankshaft drive gear teeth resulting in loss of engine power.