On July 2, 1997, approximately 1100 central daylight time, a Beech 95-B55, N6663C, experienced a failure of the rudder system while taxiing at Gregg County Airport, near Longview, Texas. The flight instructor, his student, and a passenger were not injured. The airplane was operated by LeTourneau University of Longview, Texas, under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the local multiengine instructional flight which had originated approximately 60 minutes before the incident. No flight plan had been filed. The flight instructor reported to the investigator-in-charge (IIC) that while taxiing to parking, the "student started a right turn that was too tight and I applied left rudder to stop the turn." The flight instructor further reported that there was an audible "pop" and the left rudder pedal went to the floor. He said they stopped the airplane and pushed it into its parking space. Postincident examination of the rudder system revealed that the rudder pedal bell crank from the right seat side was broken. The airplane manufacturer's Metallurgical Engineering Laboratory examined the bell crank's aft arm fracture and determined that it failed due to "overload." They further determined that there were no indications of preexisting cracks and/or material defects in the bell crank's aft arm (see attached metallurgical report).