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Air NZ general manager airline operations and safety and chief pilot David Morgan said the airline had operated about 1000 flights and carried more than 50,000 passengers since a volcanic ash cloud arrived in New Zealand airspace on Sunday.
The ash cloud was caused by an eruption in Chile more than a week ago.
"The authorities are providing excellent information about the ash, which is at high altitude and very predictable in its movement," the chief pilot said.
By adjusting cruising altitudes of its aircraft, Air NZ was able to continue to safely deliver customers to their destinations.
"Lower cruising altitudes mean we need to burn around 10% more fuel than normal but we don't believe that's a reason to stop flying, when there are perfectly safe flight paths available below the level of ash," he said.
Forsyth Barr broker Peter Young said the airline would certainly have scored "some Brownie points" with its decision to continue flying.
There was an element of discretion when making the decision to fly and that policy clearly varied company by company. It was not a civil aviation decision.
"There would be zero tolerance when it comes to the safety of their passengers and staff and Air NZ has assessed that it is all right to fly at a lower altitude on domestic and Australian routes."
Qantas and Jetstar airlines had assessed the risk to be too great so, at the expense of the public, they had decided not to fly, he said.
That decision was not sitting well with many stranded passengers, especially when they saw Air NZ planes taking off.
"It is not a good look but it is entirely their decision and they have stuck with it," Mr Young said.
Craigs Investment Partners broker Chris Timms most people were saying "well done" to Air NZ.
"They are in a financial position to allow them to do that and this is an opportunity to generate a fair amount of goodwill. This is why it is good to have a parochial airline."
A former Labour government had stepped in to buy Air New Zealand when it was in danger of being sold to overseas-based airlines, he said.
It was debatable what would have happened if the national carrier had been sold, given the current circumstances, Mr Timms said.
Air NZ spokeswoman Marie Hosking said Air NZ flights were flying below the ash cloud which had a ceiling of 8229m. The Civil Authority has raised the safe flying level from 6100m to 8200m.
Air NZ loadings were high but Ms Hosking said she could not say if that was due to other airlines being grounded.
NZPA reported that in Australia, more than 60,000 passengers had been stranded by the ash cloud.
Qantas said it could take 24 hours to 48 hours to clear just the Melbourne backlog.