A skydiving plane that crashed at Fox Glacier killing all nine people on board was newly-modified and the Civil Aviation Authority failed to identify document discrepancies relating to the changes, investigators have concluded.
Four foreign tourists, four skydive masters and their Queenstown-based pilot Chaminda Senadhira, 33, died at 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 the worst air disaster in New Zealand in 17 years, and happened just a few hours after the first Christchurch earthquake.
The Transport Accident Investigation Commission's (TAIC) 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 by engineering company Super Air Limited.
"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.
Ian McClelland, the investigator in charge, said the adventure aviation industry had flourished in the past 10 years, and rules had not kept up with the changes.
About 100,000 people were jumping from planes each year now.
"Aviation adventure activities has grown exponentially in the last 10 years, the rules have been slow to keep up and so we had a disconnect between what was in place in terms of regulatory oversight and what was happening out there in the field,'' he said today.
Recommendations by the TAIC hoped to bring the CAA rules back in line with the industry.
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.
A new rule came into effect on May 1 which saw tighter regulations around sky diving operations in New Zealand.
This rule "probably'' brought the regulator back up to pace with the ever-expanding industry, he said.
CAA director of civil aviation Graeme Harris said the CAA now had much better tools to regulate the commercial skydiving sector.
The new rule set higher standards and allowed the CAA to maintain significantly closer oversight of the activities.
Although the pilot did not meet a basic element of good airmanship, Mr Harris said, the CAA did not regulate the parachuting sector closely enough prior to the crash.
"In the intervening year and a half the regulatory landscape controlling these operations has been transformed. A great deal of work has been done to improve safety in this sector, and I am certain that it will.''
The company which modified the plane, Super Air Limited, said it would not comment on today's report until it had extensively studied it.
The skydiving company no longer operates.