Incident Overview
On 7 August 2023, a Robinson Helicopter Company R44, registered VH-HRB, was departing the Lost City in the Limmen National Park, Northern Territory. The helicopter carried one pilot and three passengers. During takeoff, the helicopter rolled to the right and collided with terrain. One passenger sustained serious injuries, while the pilot and another passenger received minor injuries.
Sequence of Events
Prior to departure, the pilot was unaware that the helicopter's left skid was against a tree root that was partially obscured by sand. As the pilot applied flight control inputs to raise the helicopter into a hover, it began rolling to the left against the tree root. In response, the pilot applied right cyclic input and then lowered the collective. The right cyclic input freed the skid from the tree root but also caused the helicopter to drift to the right. When the pilot lowered the collective to settle the helicopter, it dynamically rolled over to the right.
Investigation Findings
The ATSB determined that during takeoff with prevailing east-south-easterly winds, the pilot applied slight left cyclic to maneuver into a hover. This pushed the left skid into the tree root, causing the helicopter to initially roll around the left skid. The pilot's subsequent application of right cyclic freed the skid but led to an undetected lateral drift. Lowering the collective then resulted in a dynamic rollover as the right skid contacted the ground.
Safety Message
The ATSB emphasized the importance of smooth and controlled flight control inputs during critical flight phases. Helicopters in contact with the ground are subject to influences that can result in dynamic rollover. A thorough understanding of dynamic rollover principles and recovery methods is essential for safe takeoffs and landings, especially in unprepared areas. Operators and pilots are reminded to conduct thorough visual inspections of landing sites to identify potential hazards before takeoff, as concealed hazards are common in uncertified aerodromes and bush landing sites.