Incident Overview
During a training flight, an instructor pilot was demonstrating a confined area takeoff to a private pilot receiving advanced instruction. As the aircraft cleared the barriers, a change in wind conditions occurred.
Sequence of Events
The takeoff was initiated with a quartering head wind. As the helicopter cleared the barriers, the wind shifted and became a tail wind. The shift caused a loss of translational lift. The instructor applied full power, but this did not remedy the situation, and the helicopter lost rotor RPM. Before the instructor could reestablish a climb, the aircraft settled into the trees.
Contributing Factors
According to the investigation, a tail wind would substantially increase the power requirement for the maneuver that was being attempted. The loss of translational lift and subsequent loss of rotor RPM occurred as a result of the wind shift, and the available power was insufficient to arrest the descent.