AT&T and Verizon agreed Tuesday to a partial delay in activating their 5G networks following an outcry from US airlines, who said the rollout could lead to travel chaos.
US President Joe Biden said the move would avert major disruptions, but at least one airline, Delta, warned of the potential for cancellations despite the postponement.
The latest delay came one day after the chief executives of the largest airlines in the United States warned of a "catastrophic disruption" to travel and shipping operations if the rollout went ahead Wednesday as planned.
Aviation industry insiders expect there could still be some flight cancelations and other impacts in the coming days, but the measures announced by AT&T and Verizon are expected to prevent the worst problems.
Telecom giants spent tens of billions of dollars to obtain 5G licenses last year, but as the launch date approached, aviation industry groups raised concerns about possible interference with airplanes' radio altimeters - which can operate at the same frequencies - particularly in bad weather.
AT&T described its latest delay as voluntary and temporary, with a spokesperson saying it is working with the airline industry and the Federal Aviation Administration (FAA) "to provide further information about our 5G deployment, since they have not utilized the two years they've had to responsibly plan for this deployment."
"We are launching our advanced 5G services everywhere else as planned with the temporary exception of this limited number of towers."
A Verizon spokesperson said the company would begin 5G service on Wednesday for some 90 million Americans, but the firm has "voluntarily decided to limit our 5G network around airports."
"The Federal Aviation Administration and our nation's airlines have not been able to fully resolve navigating 5G around airports, despite it being safe and fully operational in more than 40 other countries," the spokesperson said.
It was unclear how long the pause would last.
The announcements were welcomed by Biden, who said in a statement the deal would "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."
Federal Communications Commission Chairwoman Jessica Rosenworcel commended the agreement, adding that 5G can safely coexist with the US aviation industry "just as it does in other countries around the world."
"The FAA has a process in place to assess altimeter performance in the 5G environment and resolve any remaining concerns," she said in a statement. "It is essential that the FAA now complete this process with both care and speed."
Airlines for America, a Washington lobby representing carriers, said it had not seen details of AT&T and Verizon's plans but that the "pause provides the opportunity to ensure all stakeholders, consumers and the US economy are served in the long-run."
While Delta was taking "necessary steps" to ensure safety in compliance with FAA guidelines, it warned late Tuesday it was "planning for the possibility of weather-related cancellations caused by the deployment of new 5G service in the vicinity of dozens of US airports, starting as early as Wednesday."
Fears of flight groundings
Verizon and AT&T have already twice delayed the launch of their new C-Band 5G service due to warnings from airlines and aircraft manufacturers concerned that the new system might interfere with instruments used to measure altitude.
The FAA said Sunday it had approved some transponders to be safely operated within areas where 5G will be deployed, clearing "as many as 48 of the 88 airports most directly affected by 5G C-Band interference."
But the airlines in a letter to government officials worried that the remaining limitations at those airports, as well as a large amount of equipment still uncertified, could trigger a crisis that would ground thousands of flights.
The letter was signed by CEOs of major airlines including American, United, Delta, and Southwest, as well as the leaders of shipping giants FedEx and UPS.
US air carriers also have protested against the potential costs incurred.
In a letter to employees prior to the Verizon and AT&T announcements, an American Airlines executive had warned of "major operational disruptions" due to the 5G rollout.