On September 6, 1993, at 1400 central daylight time, a Cessna 421B airplane, N747BW, sustained substantial damage near Oak Grove, Louisiana, during the landing roll. The commercial pilot was seriously injured. Visual meteorological conditions prevailed for the personal cross country flight. During an interview conducted by the investigator-in-charge, the pilot stated that the left brake failed to operate and he lost control of the airplane. He further stated that the airplane veered to the right, departed the runway, and struck a fence and trees. Examination of the airplane by the Federal Aviation Administration inspector indicated that the condition of the brake system could not be determined due to impact damage. The airplane forward baggage compartment and cockpit panel was crushed into the cabin area. According to the inspector, "skid marks at the scene indicated that the left brake was working properly."