An initial investigation indicates a supervisor tightening a rope led to a dramatic helicopter crash on Auckland's waterfront.
The chopper crashed while putting up a large metal Christmas tree on 23 November but the pilot managed to walk away virtually unscathed.
A preliminary report from the Civil Aviation Authority (CAA) says massive forces tore through the aircraft when it struck a lifting line.
It says a rigging supervisor had jumped up to grab the line which instantly tightened and touched the helicopter's main rotor blades.
The investigation is continuing and will focus on a range of factors, including the supervisor's actions, pre-flight safety briefings, and health and safety aspects.