Incident Overview
During a training flight, a helicopter impacted the ground and rolled onto its side after experiencing a high rate of descent while maneuvering. The certified flight instructor (CFI) had been flying with a student pilot for approximately one hour without any issues. On the return leg to the departure point, the CFI took over the flight controls from the student.
Maneuver Sequence
The student, a retired police helicopter pilot with 1,400 hours of experience training for his commercial certificate, reported that the CFI performed a "quick stop"—a rapid deceleration to zero forward airspeed. The CFI then initiated a right turn and lowered the collective. As the CFI began what appeared to be a right-turning autorotation, the helicopter started descending rapidly, and the student perceived that there was no forward airspeed. At an altitude of about 400 feet above ground level (AGL), the descent rate increased further around 200 feet AGL. The student reached for the collective to reduce the descent rate but found it already in the full up position. The airspeed indicator showed zero forward airspeed, and the rotor and RPM needles were aligned at the 2 o'clock position. The helicopter struck the ground at a high descent rate, having turned nearly 360 degrees since the start of the maneuver.
Witness Account
A witness observed the helicopter flying southbound in level flight before it stopped and turned right. The witness described the maneuver as a decelerating right turn, noting that the rate of descent increased while the helicopter continued turning.
Post-Impact Conditions
The CFI stated that no mechanical issues were detected with the helicopter or its engine. The density altitude at the time was approximately 4,000 feet.