Airline passengers who have endured tens of thousands of weather-related flight delays this week got a welcome respite from the headaches Saturday, despite concerns about possible disruptions caused by new wireless 5G systems which were rolled out near major airports.

Heading into Saturday, one of the biggest concerns had been whether 5G signals would interfere with aircraft equipment, especially devices, called radio altimeters, that use radio waves to measure distance above the ground that are critical when planes land in low visibility.

Predictions that interference would cause massive flight groundings failed to come true last year, when telecom companies began rolling out the new service. They then agreed to limit the power of the signals around busy airports, giving airlines an extra year to upgrade their planes.

Transportation Secretary Pete Buttigieg recently told airlines that flights could be disrupted because a small portion of the nation's fleet has not been upgraded to protect against radio interference.

But the worst fears about 5G hadn't cropped up by mid-afternoon Saturday, prompting Transportation Department spokesperson Kerry Arndt to describe flight travel as being at "near-normal" levels. But Arrndt also stressed that the Federal Aviation Administration is "working very closely with airlines to monitor summer pop-up storms, wildfire smoke, and any 5G issues."

Most of the major U.S. airlines had made the changes needed to adapt to 5G. American, Southwest, Alaska, Frontier and United say all of their planes have radio altimeters that are protected against 5G interference.

The big exception is Delta Air Lines. Delta says it has 190 planes, including most of its smaller ones, that still lack upgraded altimeters because its supplier has been unable to provide them fast enough.

"Some of our aircraft will have more restrictions for operations in inclement weather," Delta said in a statement provided to CBS News. "Safety of flight will never be in question."

The airline said it only expects minimal delays as a result.

Peter Greenberg, travel editor for CBS News, explained that potential disruptions have nothing to do with flyers' personal phones, or whether those phones are in airplane mode.

"Those don't affect the navigation," Greenberg said. "But a 5G tower can, because it's sending a signal, not for the plane. But that signal can actually disrupt the readings you're going to get on a radio altimeter, which could give the pilot a false altitude reading."

Wireless carriers including Verizon and AT&T use a part of the radio spectrum called C-Band, which is close to frequencies used by radio altimeters, for their new 5G service. The Federal Communications Commission granted them licenses for the C-Band spectrum and dismissed any risk of interference, saying there was ample buffer between C-Band and altimeter frequencies.

When the Federal Aviation Administration sided with airlines and objected, the wireless companies pushed back the rollout of their new service. In a compromise brokered by the Biden administration, the wireless carriers then agreed not to power up 5G signals near about 50 busy airports. That postponement ended Saturday.

The leader of the nation's largest pilots' union said crews will be able to handle the impact of 5G, but he criticized the way the wireless licenses were granted, saying it had added unnecessary risk to aviation.

AT&T declined to comment. Verizon did not immediately respond to a question about its plans.

Buttigieg reminded the head of trade group Airlines for America about the deadline in a letter last week, warning that only planes with retrofitted altimeters would be allowed to land under low-visibility conditions. He said more than 80% of the U.S. fleet had been retrofitted, but a significant number of planes, including many operated by foreign airlines, have not been upgraded.

"The airlines will always err on the edge of safety, and if they have to divert, they will," Greenberg said.

Delta did not expect to cancel any flights because of the issue, the airline said Friday. It planned to route the 190 planes carefully to limit the risk of canceling flights or forcing planes to divert away from airports where visibility is low because of fog or low clouds. Flight tracking website FlightAware listed nine Delta flight cancellations Saturday. None of them were tied to 5G issues, according to the airline.

In:
• 5G
• Delta Air Lines
• Airlines

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