Incident Overview
A helicopter pilot reported that after landing on a ramp, the aircraft began a 90-degree counter-clockwise turn and slid backward. The pilot had secured the helicopter for cooldown, setting the cyclic and collective friction locks and reducing engine RPM to 80 percent. While applying right pedal to counter the yaw, the helicopter continued sliding on the ice until it struck a snowbank and rolled over.
Pilot Statement
The pilot stated he was unaware that the ramp area was covered with ice because of the darkness. He noted that there were no mechanical malfunctions during the event. The helicopter's movement occurred after the governor was turned off and friction locks engaged.
Sequence of Events
After landing, the pilot deactivated the governor, applied friction locks on the cyclic and collective controls, and reduced engine RPM to 80 percent for cooldown. The helicopter then unexpectedly rotated counter-clockwise and began to slide backward. Despite pedal input to correct the yaw, the slide continued. The helicopter subsequently impacted a snowbank, resulting in a rollover.
Conditions and Observations
The incident occurred on a ramp covered with ice, which was not visible to the pilot in the dark. The pilot's actions were standard for post-landing procedures. No other factors, such as mechanical failure, were noted by the pilot.