Incident Overview
A certified flight instructor (CFI) and a dual student were practicing pinnacle approaches in a helicopter. The CFI was handling the controls as the aircraft approached a 6,318-foot pinnacle from the southeast. According to the student, the wind was from the east at 8 to 10 knots.
Loss of Control
As the CFI maneuvered the helicopter into a 4-foot hover, there was a sudden loss of tail rotor control. The helicopter began an uncommanded right turn. The CFI executed a hovering autorotation, but during the descent, the helicopter touched down on an outcropping of rock and rocked backward.
Damage
The tail stinger and tail rotor blades subsequently struck the terrain, resulting in damage to the helicopter. The extent of the damage was not specified.
Post-Accident Examination
Later, the CFI expressed a belief that the tail rotor control cables had unspooled from their drum, leading to the loss of control. However, a post-accident examination failed to reveal evidence of any pre-accident failure or malfunction.
Environmental Conditions
The density altitude at the accident site was approximately 8,600 feet. About 7 miles east, at Jeffco Airport, the wind was reported from 140 degrees at 10 knots.