What happened
During a flight following approximately one hour of unremarkable operation, a helicopter entered a high rate of descent while performing maneuvers. The instructor pilot took control of the aircraft from the student pilot to perform a "quick stop," which involves rapidly reducing forward airspeed to zero.
As the instructor initiated a right-hand turn and lowered the collective, the aircraft began a rapid descent. At approximately 400 feet above ground level, the descent rate increased significantly. By the time the aircraft reached 200 feet above ground level, the rate of descent continued to accelerate. The student pilot attempted to use the collective to arrest the descent but found the control was already in the full up position.
Witnesses observed the aircraft flying southbound in level flight before it began a decelerating right turn. The aircraft completed nearly a 360-degree turn and impacted the ground at a high rate of descent, subsequently rolling onto its side. There were no injuries reported.
The investigation
The investigation examined the aircraft's performance during the maneuver. Instruments indicated that there was no forward airspeed at the time of the incident, with the rotor and RPM needles both positioned at the 2 o'clock position. The instructor pilot reported that there were no mechanical anomalies identified regarding the engine or the helicopter systems. Environmental conditions at the time included a density altitude of approximately 4,000 feet.