By David Shepardson, Tim Hepher and Jamie Freed
(Reuters) -Disruption to U.S.-bound air travel caused by the rollout of 5G services in the United States eased on Wednesday as authorities approved more flights, but a top airline warned "irresponsible" regulatory confusion would be felt internationally for days.
Airlines and telecom companies have been at loggerheads over the deployment of 5G mobile services over concerns that the powerful signals could interfere with airplane systems.
Carriers across Asia, the Middle East and Europe cancelled flights to the United States or switched planes at the last minute on Tuesday and Wednesday, disrupting travel for thousands of passengers, over safety concerns caused by the 5G deployment.
But Japanese carriers said late on Wednesday they would restore cancelled flights and U.S. airlines said thousands of planes were operating normally after two telecom carriers agreed to delay the rollout at key airports.
The decision late on Tuesday by AT&T and Verizon Communications to delay switching on new telecom masts near key airports, just hours ahead of a wider U.S. rollout, came too late to avoid a ripple of cancellations.
Much of the initial disruption hit the Boeing 777, for decades a workhorse of long-distance air travel.
Dubai's Emirates, the world's largest international passenger carrier and the largest 777 operator, hit out at "mixed messages" as it suspended nine U.S. destinations.
The airline's longstanding president Tim Clark told CNN it had not been aware of the extent of the safety concerns until Tuesday and let rip at what he called it "one of the most delinquent, utterly irresponsible" episodes in his career.
Some 32,000 Emirates passengers over the next three days "will be completely inconvenienced as a result of flight cancellations," Clark said, adding the message about safety risks had "got through at a very, very late stage".
United Airlines, by contrast, said it was forecasting only "minor disruptions" due to remaining 5G restrictions.
International carriers are particularly exposed because of the lead time needed to prepare flights and pre-position crews ready to fly intercontinental jets home, experts said.
"The last-minute postponement happened too late to stop the crews being sent out for today's (return) flight. It just made it a nightmare," said a pilot with a major European airline.
Shares in European long-haul carriers fell by 3-4%, underperforming slightly weaker shares in U.S. airlines.
U.S. airlines and the Federal Aviation Administration have warned that the 5G frequencies and transmission strength being deployed in the United States could interfere with radio altimeter readings needed for bad-weather landings on some jets.
Radio altimeters must give clear data on the height above the ground on approach to help with automated landings and also verify that a jet has landed before allowing reverse thrust.
U.S. President Joe Biden said he had "pushed as hard I can to have the 5G folks hold up and abide by what was being requested by the airlines until they could more modernize over the years -- so 5G would not interfere with the potential of a landing".
Boeing said it was working with all parties on a "data-driven solution for the long-term".
Its 777 was last year the second-most used widebody plane on flights to and from U.S. airports with around 210,000 flights, behind the older 767, according to data from FlightRadar24.
European regulators say no risks have been found elsewhere.
The Federal Aviation Administration is frantically reviewing guidance on which airports and planes are affected.
On Wednesday, it said it had issued new approvals allowing some 62% of U.S. commercial airplanes to perform low-visibility landings at airports where 5G is deployed, up from 45% cleared previously.
Analysts said a slump in long-haul flying caused by pandemic border restrictions would limit the immediate airline impact.
"It's the off season, so in January or February airlines will be losing money and that's not counting the impact of the pandemic. At the moment they are fighting for survival," said James Halstead, managing partner at UK-based Aviation Strategy.
"Where it might hurt is that some airlines are using the same long-haul aircraft to carry freight," he added.
Airlines reporting cancellations or model switches earlier included Germany's Lufthansa, Korean Air Lines, Singapore Airlines and British Airways - all long-haul carriers with major freight operations.
(Additional reporting by Ed Copley and Josephine Mason in London, Eric M. Johnson in Seattle, Alexander Cornwell in Dubai, Ari Rabinovitch in Jerusalem, Lilian Wagdy and Moataz Mohamed in Cairo, Abhijith Ganapavaram in Bengaluru, Duncan Miriri in NairoboiEditing by Mark Potter, Bernard Orr and Richard Pullin)