On September 15, 1995, at about 1415 eastern daylight time, a Snow S2A, N4977C, veered off the left side of the runway while landing at Mountain Road Airport, Pasadena, Maryland. The pilot, the sole occupant, was not injured and the aircraft sustained substantial damage. The aircraft was being operated as a banner tow flight under 14 CFR 91 when the accident occurred. Visual meteorological conditions prevailed for the local flight, no flight plan was filed. The pilot reported that during the landing roll as he applied the brake, the airplane veered 30 degrees to the left. He stated that he attempted to correct by applying full right brake, but he was unsuccessful. The airplane continued to veer to the left and exited the runway where it collided with a tree, an automobile and a parked airplane. The FAA Inspector reported that he examined the airplane after the accident and he observed that the right brake had failed. Further examination of the right brake did not disclose the cause of the failure. The pilot reported that the most recent inspection of the airplane was an Annual Inspection, dated September 2, 1995. The airplane had flown approximately 10 hours since the Annual Inspection. According to the pilot this aircraft is equipped with a lockable non-steering tailwheel. At the time of the accident the tailwheel was locked.