The NZCAA report is below. Clearly they are looking into some of the planning, coordination and personnel issues.
Preliminary Report
ZK-HIG Accident, Auckland Viaduct Harbour
23 November 2011
Abstract
At approximately 0935 hours New Zealand Daylight Time on 23 November 2011, the pilot of ZK-HIG, an Aerospatiale AS350B2 helicopter, was engaged in a lifting operation at the Auckland Viaduct Harbour. The objective of the operation was to raise the tower of the Auckland Christmas tree from the ground into a vertical position, to allow ground personnel to secure the base of the tower.
After the tower was secured the helicopter descended slowly toward the ground. The helicopter then hovered approximately five metres above the ground, adjacent to the tower.
While the helicopter was hovering a loud bang was heard and the helicopter fell to the ground with the engine still running. Once the helicopter came to rest the pilot was extracted from the wreckage almost immediately, by ground personnel standing close by.
Factual Information
The helicopter operator was engaged by the rigging contractor for the purpose of erecting the 25 metre tall tower for the Auckland Christmas tree located at Auckland’s Viaduct Harbour.
The plan was for two lifts to be conducted. The first lift was to raise the tower from the horizontal into the vertical position using the Kevlar lifting line, the tower pivoting on two bolts in the base. Then, once in the vertical position, two more bolts were to be inserted into the base corners and three temporary cable stays would be applied to hold the tower in place. The lifting line would then be released from the helicopter’s hook and removed from the
tower by a rigger. The second lift would follow to position the ‘star’ ornament onto the top of the tower
The first lift proceeded well, until it came time to release the lifting line from the helicopters hook. The pilot then descended the helicopter toward the ground. The pilot was in radio communication with the rigging supervisor who was standing underneath the helicopter.
When the helicopter hovered at approximately five metres above the ground, the rigging supervisor was seen to jump up and grab the lifting line which was sagging below the helicopter.
The act of pulling downwards on the lifting line to release it from the helicopter’s hook instantly tightened the lifting line, which was still attached to the top of the adjacent tower, and the strop came into contact with the main rotor blades. The force of the impact of the main rotor blades on the lifting line caused massive out of balance forces within the helicopter’s rotating components, which resulted in the loss of the structural integrity of the helicopter whilst in flight. The helicopter then fell to the ground. All parties managed to escape without injury.
Injuries to persons
The accident did not result in any appreciable physical injury to any person.
Weather conditions
On the day, the wind was predominantly 10 to 15 knots from the North with good visibility.
Wreckage and impact information
The main rotor blades exhibited signs of significant impact with the hard surface of the pavement. The three arms on the main rotor ‘starflex’ were sheared by the impact forces.
The main rotor transmission and the tail boom had separated from the helicopter. The fuselage of the helicopter had come to rest close to the Christmas tree tower, facing in the opposite direction to that which it was facing at the time of the main rotor blade impact with the lifting line. The pilot’s seat had separated from the helicopter during the accident sequence.
Ongoing investigation activities
The safety investigation is continuing and will include:
• Further interviews with personnel.
• Understanding of the particulars of the pre flight safety briefings.
• Consideration of any preventative measures that could have been used.
• Consideration of the pilot’s experience and training.
• Identification of possible human factors that might be relevant to the accident.
• Consideration of health and safety aspects of the helicopter lifting operation.
An average male could reach a wire 3m off the ground, 3.4-4m if they jumped. Pulling the wire to head height would pull it down to 2m. For a cable already sagging below the helicopter, that would not give
that much lateral movement in the plane of the rotor and implies there was very little rotor to cable clearance in the first place.
The CAA drawing suggests a 25m tower and a 30m wire. The maths suggests a blade strike was inevitable if a low altitude de-hook was planned.