Incident Overview
A flight instructor was conducting an employment checkout ride for a prospective flight instructor. The instructor initiated a practice autorotation from an altitude of approximately 700 to 800 feet mean sea level, targeting the ocean shoreline (beach) with the intention of performing a power recovery. When the instructor attempted to increase power, the engine recovered to only about 70 percent. The pilot then took control and executed an emergency autorotation to the sandy beach.
Landing and Sequence
The helicopter's forward motion was between 3 to 5 knots at touchdown. The pilot reported that the wet sand acted like "glue," causing the helicopter to stop suddenly. This abrupt deceleration made the aircraft "rock forward and back." During the backward motion, a main rotor blade sliced through and separated the tail boom.
Post-Accident Findings
A post-accident engine run was performed, and no operational difficulties were noted. At the time of the accident, the temperature was 48 degrees Fahrenheit and the dew point was 43 degrees Fahrenheit. According to the carburetor icing curve chart, these conditions indicated serious icing for cruise or climb power. The aircraft was equipped with a carburetor temperature gauge; the pilot reported that carburetor heat was on and the needle was below the yellow band. The time from power off to the attempted recovery was approximately 15 to 20 seconds.
Observations
The accident occurred during a training flight involving a practice autorotation. The pilot's description of the landing surface and the subsequent dynamic behavior of the helicopter led to the tail boom being severed by the main rotor blade. The engine run showed no anomalies, and the ambient conditions were conducive to carburetor icing, though the pilot had activated carburetor heat.