Incident Overview
During a training flight, an instructor was demonstrating steep approaches to a private pilot. While in translational lift at approximately 80 feet above ground level (AGL), the instructor noticed the rotor and engine RPM begin to decay. The student pilot reported that the instructor was using a visual reference between the indicated airspeed, about 50 MPH, and the ground picture. As the descent continued, the student observed the engine speed at approximately 2900 RPM and manifold pressure at about 15 inches. Shortly thereafter, both rotor RPM and manifold pressure began to drop.
Emergency Response
The instructor stated, "we are having an engine failure," and lowered the collective control lever while increasing throttle. However, there was no reaction in manifold pressure, and the main rotor RPM continued to decrease. The instructor executed a landing in a field just short of the intended landing point. The helicopter contacted the ground at a higher than normal descent rate, causing the main rotor blades to strike the tail boom. This severed the tail rotor and tail rotor gearbox from the tailboom.
Post-Accident Examination
Examination of the engine revealed that the idle speed and mixture settings were out of adjustment. However, the specific cause of the loss of engine power was not determined. The density altitude at the time of the incident was calculated to be 7,943 feet above mean sea level.