On June 12, 1993, at 0830 Alaska daylight time, a wheel equipped Wilga 80 airplane, N909CC, registered to David Meyers of Memphis, TN, and operated by the Pilot-in-Command, slipped from its parking brake and ran into a parked Cessna 170 airplane, N2599C, registered to Ron Smith of Haines, Alaska. The business flight, operating under 14 CFR Part 91 for the purpose of fish guiding, was departing Haines, and the destination was Excursion Inlet, Alaska. The Private certificated Pilot-in-Command was not in the cockpit and was not injured. The airplane was not damaged, however, N2599C, received substantial damage. According to the Pilot-in-Command, the engine on the Wilga uses a compressed air start system and he had to use an external compressed air source. He used a dive tank and after starting the airplane he exited the cockpit and disconnected the external compressed air source. He was loading the dive tank into his pickup when the airplane began moving. According to the Pilot, the parking brake is a handle attached to a cable and the handle is pulled out and placed on a bracket to hold the parking brake on. One side of the bracket broke and allowed the cable to retract and release the brakes. The airplane struck a parked airplane before the Pilot was able to catch and stop the airplane with a rope. The Pilot stated he was not using wheel chocks.