An air safety investigator has dismissed official findings into a fatal skydiving plane crash at Fox Glacier.

Alan Daley was Civil Aviation Authority's lead investigator into the Skydive New Zealand crash that killed four tandem skydive masters, four overseas tourists and the Queenstown pilot at south Westland township's airstrip on September 4, 2010.

However, the Transport Accident Investigation Commission (TAIC) was the main investigator and its report released in May blamed the crash on the fact the plane was overweight and unbalanced.

Modifications to the aircraft to convert it from topdressing to skydiving, which pushed its centre of gravity back, caused the nose to tilt up on takeoff, which made it difficult for the pilot to control.

The owners and pilot failed to do required weight and balance calculations, the report said.

Aviation expert Barry Payne told the Coroner's Court in Greymouth earlier this week he did an independent crash report for the coroner and also blamed weight and balance as key factors.

But Daley today told the inquest the plane was capable of carrying much heavier weights without a loss of control.

''I believe weight is not a causal factor in this accident.''

The inquest earlier heard the actual weights of the nine people aboard the doomed plane were not used in crash investigations.

Daley noted weights of the dive masters and pilot would be known from aviation medical tests and it would be possible to get some idea of the passengers' weights to allow greater accuracy in determining that as a crash cause.

Claims that balance was a key crash cause were ''unconvincing,'' based on information available, he said.

The doomed plane had successfully completed 74 tandem flights with eight skydivers without anything untoward occurring.

Also, there had been thousands of similarly loaded flights in the same type of Walter Fletcher aircraft with no loss of control, he said.

Information from test flights completed last week also discounted balance as a crash factor.

Daley suggested Super Air, the engineering company that did the plane's modifications, undertook flight tests of a similar plane when he was summonsed to appear at the inquest as an expert witness, rather than on behalf of CAA.

''We've tried to recreate what the aircraft was experiencing on the day of the accident.''

Flight design expert Don McGill, of Aviation Design Solutions Ltd, told the inquest today he was involved with the controlled flight tests over two days last week, which explored possible crash theories.

The flight manual had sufficient information for weight and balance calculations, which he used for the flight tests, he said.

Several other experts have disputed weight and balance problems as causing the crash.

An expert air accident investigator, Mark Houston, an experience test pilot, agreed that weight and balance were unlikely to have caused the crash.

He said it was possible to control the aircraft when overweight and with an aft centre of gravity.

However, he conceded if skydivers had slid back when the plane took off too steeply, then the centre of gravity would go back.

- © Fairfax NZ News