On July 24, 2002, at 0745 mountain daylight time, a Grumman G-164A, N5416, was substantially damaged when the airplane ground-looped while landing at Doyle's Airfield, Two Buttes, Colorado. The commercial pilot, the sole occupant in the airplane, was not injured. The airplane was being operated by the pilot under Title 14 CFR Part 137. Visual meteorological conditions prevailed for the local aerial application flight which originated approximately 30 minutes before the accident. The pilot had not filed a flight plan. The pilot said that he was landing with a load of herbicide. During the landing roll, the airplane started to veer to the left. The pilot said he applied right rudder and right brake, but the airplane did not respond. The airplane ground looped to the left, and the right main landing gear separated from the airplane. He said all four wings appeared wrinkled, but the lower right wing was bent up. Postaccident investigation of the right brake revealed that its master brake cylinder had failed.