DALLAS (AP) — Some flights to and from the U.S. were canceled on Wednesday even after AT&T and Verizon scaled back the rollout of high-speed wireless service that could interfere with aircraft technology that measures altitude.

Carriers that rely heavily on the wide-body Boeing 777 canceled flights or switched to different planes following warnings from the Federal Aviation Administration and Boeing.

But airlines that solely or mostly fly Airbus jets, including Air France and Ireland’s Aer Lingus, seemed unaffected by the new 5G service.

By midafternoon Wednesday, airlines had canceled more than 250 flights, according to FlightAware. That was a small percentage of total U.S. flights, however, and far fewer than cancellations during the Christmas and New Year’s travel season, which peaked at more than 3,000 a day when airlines were hobbled by winter storms and large numbers of workers calling in sick because of COVID-19.

Airlines for America, a trade group, said cancellations were limited because telecom providers agreed to temporarily reduce the rollout of 5G near airports while industry and the government work out a longer-term solution.

U.S. officials had said that even with the concession, there could be some cancellations and delays because of the way 5G affected equipment on certain planes.

At O’Hare International Airport in Chicago, Sudeep Bhabad said his father-in-law’s flight to India was cancelled.

“They have to resolve this problem,” Bhabad said. “It would have been a lot better if they had resolved it way before and we knew this in advance, instead of, like, finding out when we are here at the airport.”

Similar mobile networks have been deployed in more than three dozen countries, but there are key differences in how the U.S. networks are designed that raised concern of potential problems for airlines.

The Verizon and AT&T networks use a segment of the radio spectrum that is close to the one used by radio altimeters, devices that measure the height of aircraft above the ground to help pilots land in low visibility. The telecoms and the U.S. Federal Communications Commission, which set a buffer between the frequencies used by 5G and altimeters, said the wireless service posed no risk to aviation.

But FAA officials saw a potential problem, and the telecom companies agreed to a pause Tuesday while it is addressed.

The FAA has said it will allow planes with accurate, reliable altimeters to operate around high-power 5G. But planes with other altimeters will not be allowed to make landings under low-visibility conditions.

Among the problems that may make the 5G rollout an issue in the U.S. and not other countries, according to the FAA, are that American towers use a more powerful signal strength than those elsewhere, the network operates on a frequency closer to the one altimeters use, and tower antennae point up at a higher angle.

In France, telecom providers reduce the power of their high-speed wireless networks near airports.

On Wednesday, Emirates announced it would halt flights to several American cities because of concerns about 5G but would continue flights to Los Angeles, New York and Washington.

“We are working closely with aircraft manufacturers and the relevant authorities to alleviate operational concerns, and we hope to resume our U.S. services as soon as possible,” the state-owned airline said.

Tim Clark, president of Emirates, pulled no punches when discussing the issue. He told CNN it was “one of the most delinquent, utterly irresponsible” situations he’d ever seen as it involved a failure by government, science and industry.

Japan’s All Nippon Airways said that the FAA “has indicated that radio waves from the 5G wireless service may interfere with aircraft altimeters.” It added that Boeing announced restrictions on airlines flying its 777s, and said it canceled 20 flights over the issue to cities such as Chicago, Los Angeles and New York.

Japan Airlines said it will stop using the 777 in the continental U.S. for now. Eight of its flights were affected Wednesday.

But Air France said it planned to continue flying its 777s into American airports. It did not explain why it didn’t change its aircraft as many other carriers have.

In a statement, Chicago-based Boeing Co. said it would work with airlines, the FAA and others to find a solution that would allow all planes to fly safely as 5G is rolled out. It did not respond questions about its 777.

Air India announced on Twitter it would cancel flights to Chicago, Newark, New York and San Francisco because of the 5G issue. But it also said it would try to use other aircraft on U.S. routes — a course several other airlines took.

Korean Air, Hong Kong’s Cathay Pacific and Austrian Airlines said they substituted different planes for flights that were scheduled to use 777s. Korean Air spokeswoman Jill Chung said the airline was also avoiding operating some kinds of 747s. Germany’s Lufthansa also swapped out one kind of 747 for another on some U.S.-bound flights.

British Airways canceled several planned U.S.-bound Boeing 777 flights and changed aircraft on others.

Choi Jong-yun, a spokeswoman of Asiana Airlines, said the company hasn’t been affected so far because it uses Airbus planes for passenger flights to the U.S.

However, Choi said airlines have also been instructed by the FAA to avoid autopilot landings at affected U.S. airports during bad weather conditions, regardless of plane type. Asiana will redirect its planes to nearby airports during those conditions, she said.

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FCC Chairwoman Jessica Rosenworcel said in a statement that the 5G “deployment can safely co-exist with aviation technologies in the United States, just as it does in other countries around the world.” However, she urged the FAA to conduct its safety checks with “both care and speed.”

The European Union Aviation Safety Agency said it was “not aware of any in-service incidents caused by 5G interference.”

AT&T and Verizon spent tens of billions of dollars for the 5G spectrum known as C-Band in a government auction last year.