What happened
The incident occurred during a flight training session where an instructor was demonstrating a specific maneuver to a student. The objective of the demonstration was to show the student how to perform an autorotation from a height of approximately 2 feet above ground level (AGL). To initiate this maneuver, the instructor reduced power as intended.
However, during the execution of the procedure, the instructor inadvertently applied forward cyclic control input. This action caused the front portion of the helicopter's skids to strike the ground. The impact was immediately followed by the main rotor blades contacting the surface. As a result of the initial impact and subsequent forces, the helicopter rocked backward. This motion caused the rear portion of the skids to also impact the ground. The violent rocking motion resulted in the main rotor blades slicing through the tailboom, causing significant structural damage to the aircraft.
The investigation
The investigation focused on the sequence of events leading to the collision with the terrain. Examination of the helicopter revealed that the front skids and rear skids had impacted the ground in succession. The most critical mechanical failure identified was the destruction of the tailboom, which was severed by the main rotor blades during the backward rocking motion.
Findings
The primary factor contributing to the accident was the inadvertent application of forward cyclic control by the instructor during the low-altitude autorotation demonstration. This control input caused the aircraft to pitch forward excessively, leading to the initial skid impact and subsequent catastrophic structural failure of the rotor system against the ground.
Safety message
Demonstrating low-altitude maneuvers such as autorotations requires precise control inputs. Inadvertent application of cyclic control during these critical phases can lead to immediate loss of clearance and structural damage.