The CEOs of the nation’s largest airlines again Tuesday sought to block the rollout of new 5G wireless service by AT&T and Verizon near airports, arguing the technology could interfere with a key instrument on planes and cause major disruption to air travel.

AT&T responded shortly later by saying it will delay launching 5G at a limited number of towers around airports, but it made clear its frustration with the aviation industry and the Federal Aviation Administration. Verizon followed suit later Tuesday.

The wireless carriers plan to launch the new 5G service Wednesday in many U.S. cities after agreeing to a two-week postponement earlier this month and a reduction of power of 5G transmitters near airports.

But in a letter to federal officials Wednesday, the CEOs of 10 passenger and cargo airlines, including American, Delta, United and Southwest, said the wireless service will be more disruptive than they originally thought because dozens of large airports that were to have buffer zones to prevent 5G interference with aircraft will still be subject to flight restrictions announced last week by the FAA, and because those restrictions won’t be limited to times when visibility is poor.

“Unless our major hubs are cleared to fly, the vast majority of the traveling and shipping public will essentially be grounded,” the letter said. 

The letter was addressed to Brian Deese, director of the National Economic Council; Transportation Secretary Pete Buttigieg; FAA head Stephen Dickson; and Jessie Rosenworcel, chairwoman of the Federal Communications Commission.

The new high-speed 5G service uses a segment of the radio spectrum that is close to that used by radio altimeters, which are devices that measure the height of aircraft above the ground, key during weather with poor visibility. 

"The safety concern is that when the 5G service is turned on, that the signal from 5G towers will bleed into the frequency band," Dr. Hassan Shahidi, President and CEO of the Flight Safety Foundation, told Spectrum News. "And that is used by the altimeters, and it will affect the aircraft safety systems."

The FAA has issued a notice restricting the use of certain types of altimeter equipment at 50 airports located near 5G antennas. 

The CEOs said the impact will be felt even when the weather isn’t bad. Because altimeters also provide information to other safety and navigation systems in many airplanes, multiple modern safety systems on aircraft will be deemed unusable, they wrote. 

“Airplane manufacturers have informed us that there are huge swaths of the operating fleet that may need to be indefinitely grounded,” the letter said. “In addition to the chaos caused domestically, this lack of usable widebody aircraft could potentially strand tens of thousands of Americans overseas. The ripple effects across both passenger and cargo operations, our workforce and the broader economy are simply incalculable. … To be blunt, the nation’s commerce will grind to a halt.”

The CEOs have asked the Biden administration for “immediate intervention” and for 5G sites within 2 miles of airports to remain turned off for now.

“Given the short time frame and the exigency of this completely avoidable economic calamity, we respectfully request you support and take whatever action necessary to ensure that 5G is deployed except when towers are too close to airport runways until the FAA can determine how that can be safely accomplished without catastrophic disruption,” the letter said.

United Airlines issued a statement Monday evening warning the 5G rollout would have a “devastating impact on aviation.” 

“We won’t compromise on safety – full stop,” the statement said. “But, governments in other countries have successfully designed policies to ensure the safe deployment of 5G technology and we’re simply asking the US government to do the same.”

AT&T said in a statement Tuesday that it will voluntarily defer launching 5G at towers near some airports, as it continues to work with the aviation industry and federal regulators to provide information about the technology. The telecommunications giant accused the airlines and FAA of not utilizing “the two years they’ve had to responsibly plan for this deployment.”

“We are frustrated by the FAA’s inability to do what nearly 40 countries have done, which is to safely deploy 5G technology without disrupting aviation services, and we urge it to do so in a timely manner,” the statement said. “We are launching our advanced 5G services everywhere else as planned with the temporary exception of this limited number of towers.”

In its statement, Verizon said that it had "voluntarily decided" to limit its 5G network around some airports, blaming the FAA and U.S. airlines for not being able "to fully resolve navigating 5G around airports, despite it being safe and fully operational in more than 40 other countries."

"Americans have been clamoring for 5G and tomorrow we will deliver it," Verizon said.

Dr. Shahidi told Spectrum News that the arguments being made by Verizon and AT&T about use of 5G by other countries isn’t a good comparison because "this particular C-band was approved ... with two-and-a-half times the power" compared to that of other nations.

"Other countries have limitations on the power setting, and that does not exist here in the U.S.," Dr. Shahidi said, adding: "These are not apples to apples and it's important that people really understand that."

President Joe Biden applauded the two companies for their decision to delay 5G deployment and their continued work with the Department of Transportation "on safe 5G deployment at this limited set of locations."

"This agreement will avoid potentially devastating disruptions to passenger travel, cargo operations, and our economic recovery, while allowing more than 90 percent of wireless tower deployment to occur as scheduled," the president said. "This agreement protects flight safety and allows aviation operations to continue without significant disruption and will bring more high-speed internet options to millions of Americans."

Biden called the expansion of 5G technology and promotion of competition in the internet space "critical priorities" of his, and said that Wednesday's planned 5G rollout "will be a massive step in the right direction."

"My team has been engaging non-stop with the wireless carriers, airlines, and aviation equipment manufacturers to chart a path forward for 5G deployment and aviation to safely co-exist – and, at my direction, they will continue to do so until we close the remaining gap and reach a permanent, workable solution around these key airports," he added.

The telecom companies have said previously their equipment will not interfere with aircraft electronics and that the technology is being safely used in many other countries. 

White House press secretary Jen Psaki said at a briefing Tuesday that there are "ongoing discussions" with members of the White House's economic team, who are working with the FAA, FCC, airlines and other partners on the issue.

"Our objective is of course to reach a solution around 5G deployment that maintains the highest level of safety while minimizing disruptions to passenger travel," Psaki said. "That's what we're working towards, but everyone from Secretary Pete Buttigieg to members of our economic team are closely engaged in these discussions."

"We have the safest airspace in the world," she continued. "We're committed to reaching a solution around 5G deployment that maintains the highest level of safety while minimizing disruptions to passenger travel, cargo operations and our economic recovery. We certainly understand what's at stake for both industries."

"And we believe that with continued cooperation, we can chart a path forward, but certainly minimizing flight disruptions ensuring safety and travel is a top priority," Psaki added.

The FAA said in a statement Monday that it “will continue to ensure that the traveling public is safe as wireless companies deploy 5G.” 

"The FAA continues to work with the aviation industry and wireless companies to try to limit 5G-related flight delays and cancellations," the agency said.

The Associated Press contributed to this report.