What happened
A certified flight instructor was performing a demonstration of a 180-degree turn autorotation with a power recovery. The maneuver began at an altitude of approximately 600 feet above the ground. While approximately three-quarters of the way through the turn, the instructor observed that the rotor speed had decreased. Upon attempting to return the throttle to full power, the engine failed to respond. The instructor continued the approach, which resulted in a hard landing on the heel of the left skid and caused the helicopter to roll over.
The investigation
Mechanical examinations of the helicopter revealed no evidence of a system malfunction or mechanical failure. During a functional check, the engine was found to operate within a range between idle and moderated power. An inspection of the airframe showed that the skids had spread and the landing gear damper assembly was fractured.
Findings
According to FAA Advisory Circular AC 61-13A, during the flare phase of an autorotation, the cyclic control should be moved forward to level the helicopter for landing. The circular also specifies that when making a landing, the pilot should allow the helicopter to descend vertically and apply collective pitch smoothly to check the descent and cushion the impact.