Faulty suspension wires and poor engineering are being blamed for a large eagle sculpture plunging to the ground at Wellington Airport during a 6.2 magnitude earthquake in January last year.
The sculpture - which weighs more than a tonne - fell down in the earthquake when all but one of its suspension wires failed.
A WorkSafe investigation has found the eagle's failure was possibly due to shortcomings in the engineering process.
It said the engineering consultancy firm, Dunning Thornton Consultants (DTC), made significant errors in its calculations for what the wires could cope with and did not do enough to ensure it would be safe.
WorkSafe said it could not prove the engineering firm breached health and safety laws.
An engineer advising WorkSafe, Jack Main, said DTC never weighed the eagle and thought it was about 330 kilograms lighter than it really was.
Mr Main said DTC approved suspension wires that had been poorly crimped, and accepted evidence that showed the wires could fail early.
He said the earthquake that caused the structure to fail was not large, and the largest extra force experienced by the eagle sculpture was only 5.39 percent greater than its own mass.
He said this was tiny in comparison to the 300-percent DTC thought they had in reserve.
WorkSafe said it could not prove the firm had breached health and safety laws and has laid a complaint with the Institute of Professional Engineers for further consideration.
In a submission to WorkSafe, Dunning Thornton Consultants said it was not responsible for the wires failing, and that many of Jack Main's conclusions were incorrect.