On February 28, 1994, at 1515 eastern standard time, a Cessna 421, N421HA, collided with a taxiway light at the LaGrange/Callaway Airport, LaGrange, Georgia. The Federal Aviation Administration (FAA) Inspector's proficiency flight operated under 14 CFR Part 91, with no flight plan filed. Visual weather conditions prevailed at the time of the incident. The airplane sustained minor damage to one propeller blade; the two FAA Inspectors were not injured. The flight departed Atlanta, Georgia, at 1415 hours. The pilot had completed a full stop landing on runway 13, and was back taxing on taxiway "A" for a takeoff. As the airplane approached taxiway "T", the passenger reported that he was asked by the pilot to check the right brake. The passenger pumped the brake, and it did not respond (see attached passenger statement). At this point, the pilot applied left braking and swerved the airplane off of the taxiway. According to the pilot, the collision with the taxiway light occurred while attempting to avoid, what he felt was, an imminent collision with another airplane taxing southeast on taxiway"A". The pilot elected to exit taxiway "A" 325 feet short of the centerline of taxiway "T". As the airplane rolled across the grass, one of the left propeller blades struck a taxiway light. The approaching aircraft turned left on taxiway "T", and continued to the terminal ramp (see attached airport layout). The subsequent examination of the brake assembly failed to disclose a mechanical problem with the brake system. During the functional check of the brake assembly, both left and right pedals were applied from a static position. During this phase of functional check, the right brake assembly required more pressure than the left. During the dynamic check, the airplane was taxied at different speeds. At each speed range braking was smooth and positive. The visual examination showed normal brake pad wear, and there was no air detected in the brake fluid system. During a subsequent telephone conversation with the Director Of Maintenance, he stated that there had not been any other pilot reports of braking problems with N412HA before and since this account. Additionally, there has not been any additional maintenance performed on the brake system since the on site examination.