Incident Overview
A certified flight instructor (CFI) was demonstrating a 180-degree turn autorotation with a power recovery to a student. The maneuver was initiated at approximately 600 feet above ground level. About three-quarters through the 180-degree turn, the CFI observed that the rotor speed was low. When he attempted to return the throttle to full power, the engine did not respond.
Accident Sequence
The CFI continued the approach without engine power, resulting in a hard landing on the heel of the left skid. During the impact, the helicopter rolled onto its side. The CFI was not reported injured, and no other occupants were on board.
Post-Accident Examination
An examination of the helicopter revealed no mechanical problems or system malfunctions. A functional check of the engine showed it operated between idle and a moderated power range, but full power was not verified. The airframe sustained damage: the skids were spread apart, and the landing gear damper assembly was fractured. The examination confirmed that the aircraft was structurally compromised but did not identify a pre-existing defect.
Guidance from Advisory Circular
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 in preparation for landing. The circular also states that if a landing is to be made, the pilot should allow the helicopter to descend vertically and apply collective pitch smoothly to check the descent and cushion the landing.