Incident Overview
A helicopter operating as a visual flight rules on-demand passenger flight under Title 14, CFR Part 135, was involved in an accident during a moose tranquilizing operation. The purpose of the flight was to tranquilize moose for capture and collaring. The incident occurred when the darted moose exhibited extreme behavior.
Operational Details
According to the company's chief pilot, the helicopter was used to shoot a moose with a tranquilizer dart and then to block the animal from moving into a hazardous area. The company's standard practice at the time called for the helicopter to hover or maneuver approximately 10 feet above the ground, maintaining no closer than 10 feet horizontally from the darted animal. The pilot and a scientist aboard the helicopter considered these distances appropriate.
Sequence of Events
An airplane pilot orbiting above the scene reported that the moose charged the helicopter. As the helicopter attempted to evade the moose, the animal reared or jumped, making contact with the helicopter's tail rotor. The helicopter pilot subsequently experienced a loss of directional control and executed a hovering autorotation to the ground.
The impact caused the flex coupling between the drive shaft and the tail rotor gearbox to fail. The spinning drive shaft then cut through the tail boom, separating the tail from the rest of the airframe.
Post-Incident Changes
The chief pilot noted that this was the first occurrence of extreme, erratic behavior from a darted animal within the company's experience. In response to the incident, the company revised its operating procedures. The updated protocol now requires pilots to maintain an altitude of 30 feet above the ground and a horizontal distance of 30 feet from any darted animal.