On April 27, 1994, at 0800 mountain daylight time, a Beech 1900C, N141UE, operating as United Express Flight 5840, sustained minor damage while in cruise flight when a portion of a propeller blade separated from the number one engine. The 2 crew members and 19 passengers were not injured. The flight was on an IFR flight plan and was operating under 14 CFR Part 135 when the incident occurred. The flight departed Bismarck, North Dakota, at 0555 and was in the vicinity of Cheyenne, Wyoming, en route to Denver, Colorado. According to the crew, the flight was at 15,000 feet msl in clear air when the propeller failure occurred. Following the loss, the crew stated they secured the engine and proceeded to Denver due to unfavorable weather for an emergency landing in Cheyenne. The propeller was a Hartzell HC-B4MP-3A/MI0877K. It was removed and shipped to Hartzell for examination. The Hartzell report is attached and provides information that the leading edge tip end of the number three blade separated in a jagged manner and the tip was not recovered. The trailing edge of the blade remained intact almost to the tip; however, the outer shin laminates had separated. No other discrepancies were noted. Following the examination by Hartzell, the failed blade was sent to Wright Patterson Air Force Base for further examination by the composite section of their materials laboratory. The Wright Patterson report is attached and provides information that the blade failed due to apparent impact damage on the leading edge. The source of the impact damage was not discovered.