An operator of aircraft grounded by the Civil Aviation Authority says the planes are robust and have a good safety record.

Air Safaris has three Gippsland GA8 Airvan for scenic flights in the Aoraki/Mt Cook and Westland Tai Poutini national parks but they're out of action following the CAA directive yesterday.

The authority grounded 21 of the planes following similar action overseas because of safety concerns.

Australian and European authorities grounded planes following a crash in Sweden on July 14 which killed nine people on board.

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The skydiving plane was at 4000m and CAA director Graeme Harris said that based on the initial investigation it appeared it had suffered structural failure.

"At this time, the root cause of the accident cannot be confirmed," he said.

Air Safaris chief executive Richard Rayward said although the grounding happened during the low season, it meant it was difficult to deal with smaller groups.

"All our other aircraft are nearly twice the size so it is a bit of a nark at the moment not be able to deal with smaller number of people," he said.

He had contacted the Australian manufacturer of the overhead wing plane which has the capacity for seven passengers.

''There's not been any hint of anything like this. It [the Swedish accident] happened at slow speed where you would normally not get any structural problem.''

His company was the first to get the planes into New Zealand in 2002 and they had proven to be very reliable, meeting high, relatively modern, operating standards.

Rayward said the CAA had given the company warning before issuing the suspension to fly notice and had few options after the overseas authorities grounded a total of 228 of the single-engine planes around the world.

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''The CAA found themselves with no choice but to follow suit,'' he said.

There were indications the grounding could be for about a fortnight but Rayward said it could be lifted quickly if there were no inherent problems found with the plane.

Harris has said the CAA did not take these steps lightly but when there was a reasonable doubt about the safety of an aircraft, the flying public, operators and pilots of the affected aircraft must be satisfied that the authority would act with their safety as a priority.

"Whilst I regret any inconvenience this grounding will cause and acknowledge its significant commercial impact; I simply cannot compromise when I have information that indicates any unacceptable risk."

Australia's Civil Aviation Safety Authority has suspended operations of the plane for 15 days. A spokesman told the ABC that the GA8 was first certified in 2008 and had "not had a difficult safety history" before the crash.

A witness to the July 14 crash said she heard a loud noise from above before she saw the plane going straight down and crashing into an island in the north of the country.