) -- Ash from a volcano in Iceland was hampering flights in Ireland and Scotland on Tuesday, but trans-Atlantic flying continued to be largely unaffected.

Eurocontrol, which coordinates European air traffic control, said the ash is not expected to affect trans-Atlantic flights because it is mostly north of the usual routes and did not ascend above 35,000 feet, according to

The Associated Press

. Trans-Atlantic aircraft typically fly above 37,000 feet.

"At this time we continue to see no operational impact on our Trans-Atlantic operations,"


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spokesman Anthony Black said Tuesday morning. Delta has about 80 daily trans-Atlantic departures to Europe.

Black said the carrier is allowing passengers to make changes without paying fees if their flying involves the Scottish cities of Aberdeen, Edinburgh or Glasgow or Newcastle in northeastern England. Passengers scheduled to fly today or tomorrow must get their tickets reissued by May 27 and fly by May 31.


on Monday canceled three flights to Scotland, including two to Edinburgh and one to Glasgow, enabling passengers to get a refund or to change without fees. United

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spokesman Michael Trevino said that so far, the airline has not cancelled any other flights.


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has not canceled any service, but spokesman Tim Smith said flights involving Helsinki and Manchester are flying more southern routes, adding two hours to the Helsinki flight time and one hour to the Manchester flight time. American operates 41 daily round trips to Europe.

US Airways


said its two dozen daily trans-Atlantic flights from Charlotte and Philadelphia continue to operate normally.

Unlike U.S. carriers, some European airlines have been heavily impacted by the ash. The


reported that about 500 flights could be canceled as ash from Iceland's Grimsvotn volcano moved over parts of Scotland. Regulators said airlines must secure permission to fly to and from the area.

President Obama, who is on a state visit to Europe, cut short his stay in Ireland on Monday due to concerns about the ash cloud.

The low-cost Irish carrier


challenged the regulators' findings. It sent airplanes into Scottish airspace and they "encountered absolutely no problems, Ryanair's CEO Michael O'Leary told


. "There's no cloud over Scotland. There's no dusting of ash on the airframe or the wings. The airspace over Scotland should never have been restricted in the first place."

-- Written by Ted Reed in Charlotte

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Ted Reed