On March 21, 1994, at 1205 mountain standard time, a Piper PA-32- 300, N5251S, sustained substantial damage when it struck a ditch embankment during landing roll following a forced landing on a county highway near Ellsworth, Nebraska. The airplane had a total loss of engine power while in cruise flight at 10,000 feet msl. The commercial pilot and the four passengers aboard the airplane were not injured. The personal flight originated at Ainsworth, Nebraska, with an intended destination of Steamboat Springs, Colorado. An IFR flight plan was filed, and visual meteorological conditions prevailed at the time. The engine was examined by a Federal Aviation Administration Airworthiness Inspector, and a Certificated Airframe and Powerplant Mechanic. They found the impulse coupling on the left magneto had failed and was jammed in the accessory gear train. The crankshaft drive gear was found to be sheared from the crankshaft. The maintenance records were examined, and show that Airworthiness Directive 78-09-07 R3, which pertains to inspection of the magneto impulse coupling, was complied with on January 19, 1994. The airframe had accumulated 10 flight hours since the inspection.