Tens of thousands of travellers were stranded Monday after ash from Chile's volcanic eruptions prompted Australian airlines to ground many domestic and international services.
Strong winds have carried the ash more than half way around the world, over the southern Atlantic and southern Indian Oceans to Australia and New Zealand since Chile's Puyehue volcano erupted more than a week ago.
Australia's Qantas said all flights in and out of the southern island of Tasmania and to New Zealand were grounded Monday.
Three Qantas international services to Buenos Aires and Los Angeles were also cancelled, the airline said, but flights in and out of Melbourne had now resumed.
A total of 110 Qantas flights were cancelled on Sunday and Monday, delaying at least 20,000 Qantas travellers and a further 12,000 passengers on Qantas's offshoot Jetstar.
"It's down to our safety standards. Our Qantas group policy is that if there is any sign of ash cloud around we won't operate," airline spokeswoman Olivia Wirth told state broadcaster ABC.
Aviation authorities and airlines are closely monitoring the plume, with Virgin Australia saying Monday it believed it was safe to fly to Melbourne, Tasmania and New Zealand, adding its planes would fly around or under the ash.
"We decided to resume services based on information that we received from the Bureau of Meteorology and also the Volcanic Ash Advisory Centre," a spokeswoman said.
When Iceland's Eyjafjoell volcano erupted last year, its vast ash cloud grounded more than 100,000 planes as authorities in Europe fretted over potential damage from the razor-sharp ash particles to jet engines.
But there are no official or industry-wide standards regarding volcanic ash and many European airlines, suffering hefty losses and grappling with millions of stranded passengers, were angered at their governments' caution.
In New Zealand, the Civil Aviation Authority (CAA) said the cloud now covered most of the country and was likely to remain for the next 24 hours.
Spokesman Bill Sommer said the authority believed it was safe to fly under the cloud, but the decision on whether to fly rested with individual airlines.
Air New Zealand said it had operated 473 flights on Sunday, carrying more than 26,500 passengers around the country and across the Tasman, after working with experts to make adjustments to flight paths and cruising altitudes "so as to completely avoid the ash".
"It would have been far easier to simply cancel flights and it's taken a lot of effort by our operations teams to develop alternative flight plans to continue to get passengers to their destinations," chief pilot Captain David Morgan said.
The airline said to avoid the ash cloud, trips to Australia had been given new flight paths heading further north than normal before crossing the Tasman, while domestic services were operating at a maximum 5,500 metres (18,000 feet).
"The extra distance involved required the use of 10 percent more fuel, but has meant customers were able to safely get to where they needed to go," Morgan said in a statement.
"We will not fly through ash and are constantly taking guidance from CAA and the Metservice to ensure we can continue to carry passengers only where safe routes and altitudes are available."
Australia's Volcanic Ash Advisory Centre said a similar ash cloud had not been seen in the region in two decades and this one was likely to continue to travel around the globe, after passing over Tasmania and New Zealand.
"It went over the south Atlantic, south of South Africa and into the southern Indian Ocean and around the south of Western Australia," said Graham Weston, volcanic ash forecaster at the Darwin centre.
"It's almost circumnavigated the world."
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