Incident Overview
During a training flight, a dual student pilot was practicing autorotations with a reduced engine RPM setting and without the use of carburetor heat. On the fourth autorotation, the engine experienced a total loss of power. The certified flight instructor (CFI) assumed control and continued the autorotation.
Hard Landing
When the helicopter descended to between 7 and 10 feet above the ground, the CFI applied up collective without correcting for the increased torque (rotor pitch increase). This caused the helicopter to make an abrupt left turn and land hard, resulting in damage to the skids and the tail boom assembly.
Engine and Weather Conditions
After the accident, the helicopter was recovered from the site, and the engine was found to operate normally. The prevailing temperature was 94 degrees Fahrenheit with a dew point of 63 degrees Fahrenheit. According to the FAA Icing Probability Chart, the carburetor was susceptible to carburetor icing at glide power under those conditions.