NTSB Identification: MIA97LA222.
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Accident occurred Monday, July 28, 1997 in LAKE BUENA VIST, FL
Probable Cause Approval Date: 05/29/1998
Aircraft: Waco YMF5, registration: N14128
Injuries: 3 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
During cruise flight, the pilot noted an engine vibration followed by a total loss of engine power. He made a forced landing, but was unable to reach suitable terrain. During the landing rollout, he observed a ditch and intentionally ground looped the airplane, but the airplane collided with a pole. Examination of the propeller revealed the propeller retention nut was hand tight. Galling was present on the propeller hub mounting flange and the rear cone. Disassembly of the engine assembly revealed the crankshaft was broken at the counterweight flange. Visual inspection of the shear surfaces on the crankcase showed tell tale benchmarks that appeared to have originated at the oil way plug threads and progressed through approximately one fifth of the crank circumference. Interviews with personnel involved with the installation revealed they had retorqued the propeller, but had not followed accepted industry practices in establishing proper hub to rear cone contact surfaces.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: failure of maintenance personnel to follow installation procedures pertaining to the torque of the propeller retention nut, which resulted in a loose propeller retention nut, subsequent fatigue failure of the crankshaft, and loss of engine power. The lack of suitable terrain for an emergency landing was a related factor. Full narrative available
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