Four foreign tourists, four skydive masters and their Queenstown-based pilot Chaminda Senadhira, 33, died about 1.15pm on September 4, 2010, soon after the Fletcher FU24-954 turboprop they were in took off from Fox Glacier Airport.
The incident was just a few hours after the first Christchurch earthquake and the worst air disaster in New Zealand in 17 years.
The Transport Accident Investigation Commission's final report into the incident, released this morning, revealed the plane had been converted from an agricultural crop-duster to a parachute-drop plane only three months earlier.
"The modification ... had been poorly managed and discrepancies in the aeroplane documentation had not been detected by the Civil Aviation Authority which had approved the change in category,'' the report found.
The new owner and operator of the plane, Skydive NZ, had not completed weight and balance calculations before it entered service.
As a result the plane was flown outside its loading limits every time it carried a full load of eight passengers.
Witnesses reported the plane took-off normally before pitching upward until almost vertical. The plane then performed a "wing-over'' and plunged vertically into a field.
An interim report issued soon after the incident recommended to the CAA that no more than six passengers be carried in the forward cabins of other FU24s used for parachuting operations.
It estimated the aircraft was 5kg over its maximum certified limit of 2203kg and the plane's centre of gravity was 0.115m outside the allowable aft (towards the tail) limit of 0.645m.
The report also urged pilots to weigh passengers and their equipment before each flight and ensure they were positioned inside the aircraft so as not to upset the centre of gravity.
The CAA has implemented the recommendations and said no parachuting operation can go ahead without weight and balance checks.
The interim report also recommended parachutists be restrained in planes to stop them moving about.
Today's report also recommended that the CAA takes necessary steps to ensure high engineering standards are maintained by the company that made the modifications and other aircraft maintenance organisations.
It also said the CAA needed to ensure all parachuting operations conformed to civil aviation rules.
The CAA said it had accepted those recommendations and implemented new risk-based surveillance processes to improve audits.
It has also carried out spot checks on parachuting operations.
