On August 12, 1994, at 1700 Alaska daylight time, a wheel equipped Helio-Courier H-700 airplane, N4059H, registered to Charlie Warbelow and operated by 40 Mile Air, LTD, of Tok, Alaska, experienced a brake problem during landing on an airstrip located 40 miles southwest of Tok on the east fork of the Robertson River. The Air Taxi flight, operating under 14 CFR Part 135, departed Tok and the destination was the accident site. A company flight plan was in effect and visual meteorological conditions prevailed. The pilot and the three passengers were not injured. The airplane was substantially damaged. According to the pilot, as he attempted to stop the airplane through the use of his brakes, the left brake went soft. He allowed the airplane to continue rolling and just prior to running into a ditch he intentionally ground looped the airplane. The tailwheel hit the ditch and the fuselage buckled behind the aft baggage compartment. The pilot stated the torque plate had sheared from the brake calipers and the brake line had broken. The passengers were employees of the American Copper and Nickel Prospect. The operator did not submit their names on the NTSB Form 6120.1/2 at the time of the accident.