The airplane incurred minor damage during a forced landing at 1850 Eastern time following an engine failure. The airline transport pilot and the two passengers aboard were not injured. Visual conditions prevailed. The airplane was operating IFR as a Part 135 on-demand air taxi flight. About 10 minutes after takeoff, with the airplane level at 6000 feet, the pilot noticed engine oil pressure had dropped. About two minutes later, the engine began to run rough and oil pressure dropped further. Shortly after, the engine quit and the pilot made a forced landing to a road. During the landing rollout, the right wing hit a road sign. Examination of the engine revealed a hole through the top of the case between the number 5 and number 6 pistons.
