On April 8, 2000, about 1600 mountain daylight time, a PDPS PZL-Bielsko, SZD-45A Ogar, N54AS, registered to and operated by the pilot as a 14CFR91 personal pleasure flight, was substantially damaged when a portion of the propeller blade separated while in a cruise flight configuration. The commercial pilot, the sole occupant of the aircraft, was not injured. Visual meteorological conditions prevailed and no flight plan was filed. The flight originated from Coeur D'Alene, Idaho (COE), approximately four hours prior to the accident. The pilot stated that the aircraft was in a powered cruise configuration at 7,500 feet mean sea level (msl) when one blade of the Maloof (C4.5X58) propeller separated from the propeller hub. The pilot initiated a descent and subsequent forced landing at Libby Municipal Airport (S59), Libby, Montana, without further incident. An FAA Inspector from the Spokane, Washington, Flight Standard District Office inspected the aircraft after the accident and reported that the propeller blade separated near the propeller blade root. The inspector also stated that there appeared to be a preexisting crack in the area of the separation.