What happened
A dual student pilot was conducting practice autorotations at reduced engine RPM without utilizing carburetor heat. During the fourth autorotation of the session, the engine experienced a total loss of power.
The Certified Flight Instructor (CFI) took control of the aircraft to continue the autorotation procedure. As the helicopter was positioned between 7 and 10 feet above the ground, the CFI applied up collective. However, the instructor did not correct for the resulting increase in torque caused by the increase in rotor pitch. This lack of correction caused the aircraft to make an abrupt left turn and land hard, resulting in damage to the skids and tail boom assembly.
The investigation
Upon recovery of the aircraft from the accident site, the engine was found to be operating normally. Environmental conditions at the time of the event included a temperature of 94 degrees F and a dew point of 63 degrees F. Analysis using the FAA icing probability chart indicated that the carburetor was susceptible to carburetor icing while in glide power.