The student pilot and the flight instructor performed a preflight inspection of the helicopter and then moved it from the hangar onto an area of soft, muddy ground outside. They pushed the helicopter as far away from the hangar as they could due to the soft ground, about 25 to 30 ft. The student pilot described that where the helicopter was positioned, it was “leaning back” with the aft portion of both skids several inches deep in the mud. During the subsequent takeoff attempt, the student pilot noted that the helicopter required the application of additional engine power than he had observed during previous takeoffs before it became “light on the skids.” During a postaccident interview, he postulated that the helicopter might have been “stuck in the mud.” The flight instructor then felt that the helicopter’s tail might strike the ground, so he nudged the cyclic control forward. Immediately after, the helicopter began moving forward toward the hangar in a significantly nose low attitude. Despite their subsequent control inputs, neither pilot was able to arrest the helicopter’s forward motion and it struck the hangar less than 2 seconds later and came to rest on its right side. The helicopter’s fuselage, tailboom, and main rotor blades were substantially damaged during the accident sequence. The flight instructor reported that there were no preimpact mechanical malfunctions or failures of the helicopter that would have precluded normal operation, and FAA inspectors who examined the helicopter after the accident were unable to find evidence of a preimpact mechanical malfunction or failure of the flight controls that would have precluded normal operation. Based on this information, it is likely that the helicopter suddenly dislodged itself from the soft, muddy ground during the takeoff when the flight instructor applied nose down cyclic input, which resulted in an unexpected, rapid forward movement and collision with the hangar. Had the flight instructor recognized the abnormal amount of engine power being applied by the student and discontinued the takeoff attempt, it is likely that the accident could have been avoided.