On May 15, 1999, at 1245 central daylight time (cdt), an Engleman Pitts S1, N64DE, operated by a commercial pilot ground looped while landing at the Coles County Memorial Airport, Mattoon, Illinois. The pilot was not injured. The airplane was substantially damaged. The 14 CFR Part 91 personal flight was operating in visual meteorological conditions without a flight plan. The local flight originated from Mattoon, Illinois, at 1157 cdt. The pilot reported that prior to the accident he made three landings on Runway 17 which was a grass airstrip. He then flew in the local area for approximately 20 minutes and came back to land on Runway 11 (6,501' x 150'). The pilot reported the local winds were from 170 degrees at 10 knots. The pilot reported he made a 3-point landing and the initial portion of the landing roll was normal. He reported the airplane then began to "...veer sharply to the right." The pilot reported he was unable to correct the directional control and the airplane continued to the right. The left main gear collapsed and the left lower wingtip along with the propeller contacted the runway prior to the airplane coming to rest on a heading of about 180 degrees. An inspector from the Springfield, Illinois, Federal Aviation Administration Flight Standards District Office examined the airplane after the accident. The inspector reported that he was unable to find any failure/malfunction of the airplane's brake system. He did state that there was a fuel line which ran near the left brake pedal and it was possible that line interfered with the pilot pressing on the brake.