From mask requirements to waived change fees, the pandemic has dramatically changed what it's like to fly. But beginning early next year, even more changes could be coming to air travel — ones that have nothing to do with the coronavirus.

These changes could lead to flight delays or diversions affecting tens of millions of passengers across hundreds of thousands of flights, according to aviation industry estimates.

It all comes down to a political fight over 5G, the next-generation cell service technology that's begun to be supported in the latest smartphones. Here's what you need to know:

The concern

Transportation regulators are concerned that a version of 5G that's due to be switched on in January could interfere with some airplane instruments, and many aviation industry groups share those fears — despite reassurances from federal telecom regulators and wireless carriers.

Specifically, the Federal Aviation Administration is worried that 5G cellular antennas near some airports — not air travelers' mobile devices — could throw off readings from some aircraft equipment designed to tell pilots how far they are from the ground. Those systems, known as radar altimeters, are used throughout a flight and are considered critical equipment. (Radar altimeters differ from standard altimeters, which rely on air pressure readings and do not use radio signals to gauge altitude.)

The agency is so concerned that this month it issued an urgent order forbidding pilots from using the potentially affected altimeters around airports where low-visibility conditions would otherwise require them. This new rule could keep planes from getting to some airports in certain circumstances, because pilots would be unable to land using instruments alone.

It's not entirely clear which airports this rule may affect. When it rolled out the order, the FAA said the exact airports would be specified later once it had more information from wireless carriers about where the 5G infrastructure might be placed.

The clock is ticking. On Jan. 5, wireless carriers are expected to activate the 5G service that relies on the radio frequencies the FAA is worried about.

According to a service map by the Federal Communications Commission, big swaths of California, Florida, New England, Texas and the midwest will gain 5G coverage. But aviation groups warn that it could jeopardize some of the nation's largest airports, including in Los Angeles, New York and Houston.

How 5G signals work

The 5G signals will travel over radio frequencies that are collectively known as the C-Band. This band of airwaves is attractive to wireless carriers because it offers a good balance between cellular range and capacity — two key features of any wireless network. (Other sets of airwaves besides the C-Band are also used to carry 5G, but the current debate focuses on just the C-Band frequencies.)

On the spectrum of radio frequencies used for wireless communications, the C-Band sits right next to the band of frequencies used by the aircraft altimeters. Well, almost: The two are intentionally separated by a so-called guard band — essentially "blank" airwaves — to safeguard against interference.

To further address any aircraft risks, Verizon and AT&T — which owns WarnerMedia, CNN's parent company — offered in November to limit the power of their 5G antennas and to take other precautionary measures. Separately, the companies also agreed to postpone the 5G rollout from Dec. 5, 2021 to Jan. 5, 2022.

But that hasn't been enough to allay the concerns of the FAA, whose 11th-hour order would have "an enormous negative impact on the aviation industry," the CEOs of Boeing and Airbus wrote in a letter Monday to the Department of Transportation. The CEOs added: "We agree that 5G interference could adversely affect the ability of aircraft to safely operate."

The letter cites an estimate published by the industry group Airlines for America, which predicts the FAA restrictions will disrupt 345,000 passenger flights, 32 million passengers and 5,400 cargo flights. The FAA's own order estimates that 6,800 US airplanes could be affected by the plan, along with 1,800 helicopters.

That's a lot of disruption over a fear of possible air safety risk, an issue that the FCC spent years researching before ultimately opening up the C-Band for 5G usage in a 2020 order.

In addition to their own proposed changes, wireless carriers should be required to do more — such as further reducing 5G power levels and ensuring that antennas are pointed below the horizon, an aviation industry coalition said in a letter to the FCC this month.

5G in other countries

Technology experts say that while 5G antennas could theoretically lead to interference around airports, the potential for interference is an ever-present feature of all wireless communications — not just 5G — and that so far regulators around the world have done a good job of handling it.

"It's worth noting that about 40 other countries have approved use of 5G in C-Band," wrote Harold Feld, a telecom expert at the consumer group Public Knowledge, in a November blog post on the issue.

"Japan in particular operates 5G networks today much closer to the altimeter band than the 220 MHz separation adopted by the FCC. So far, there are no reliable reports of any harmful interference with air altimeters," Feld wrote. "It's possible for the FCC to make a mistake on this, sure," Feld added. "But regulators in 40 different countries? And with no incidents where operation has already begun?"

According to the aviation industry, countries such as Japan and South Korea operate 5G at a fraction of the power levels permitted in the United States, while Canada has an interim rule requiring antennas be tilted downward and in Europe, the guard band is 100 megahertz wider than in the US.

According to the wireless sector, however, countries such as Japan only impose power limitations on frequencies the United States doesn't even plan to use for 5G. And until 2023, when 5G is more fully rolled out in the C-Band, there will actually be much more "blank" spectrum than just the guard band separating cellular traffic from altimeter operations — as much as 400 MHz altogether, according to the FCC's 2020 order. That may give everyone involved more time to assess any real-world risks and to adapt.

Should you worry?

So who is right, and do air travelers have anything to fear?

In his experience, Feld wrote, FCC engineers who make decisions about spectrum are "extremely aware that if they screw up people could die" — which he said reveals how the FAA publicly contradicting the FCC is less about a realistic danger to public safety than a type of bureaucratic power struggle that has become increasingly common across the federal government. (For its part, the Transportation Department has been expressing reservations about the 5G rollout for over a year.)

The FCC didn't immediately respond to a request for comment for this story.

The FAA isn't the only agency to issue dire warnings about potential interference from changes in how the US uses its wireless airwaves. In 2019, the Pentagon said that opening up a different range of frequencies for 5G usage — a set of airwaves known as the L-Band — could interfere with military GPS systems. And in another high-profile fight, the FCC has been at odds with NASA and NOAA over the impact that 5G could have on weather satellites.

In a statement earlier this month, the FAA said it was continuing to work with the FCC and telecom carriers to find a solution. Since the wireless carriers have already proposed some changes, and the aviation industry is calling for more, the haggling appears to be focused on how far the telecom companies will ultimately need to go. The negotiations also reflect the aviation sector's approach to risk in what is inherently a life-or-death business and where small margins of error are not tolerated.

A person familiar with the negotiations told CNN Business that the FCC, the FAA and all industry participants have a working plan to limit the impact of the FAA's aircraft restrictions. After the FAA outlines the specific airports that will be subject to the limitations — again, based on infrastructure data provided by the wireless carriers — the FAA will call on altimeter manufacturers to test their equipment against the new operational conditions proposed by the telecom industry. Altimeters that prove to be unaffected would then be deemed safe to use, making it possible to avoid some of the feared flight delays and diversions.

"Right now there is a nonstop, constant exchange of information going on between the federal agencies and the industry stakeholders on both sides," the person said. "Meetings at all levels, every day. There is a plan in place and everyone is in agreement on what that plan is and executing on that."

On Wednesday afternoon, telecom and aviation industry officials released a joint statement to the same effect.

"We are pleased that after productive discussions we will be working together to share the available data from all parties to identify the specific areas of concern for aviation," the statement said. "The best technical experts from across both industries will be working collectively to identify a path forward, in coordination with the FAA and FCC."

The FAA said in a subsequent statement it is "encouraged that avionics manufacturers and wireless companies are taking steps to test how dozens of radio altimeters will perform in the high-powered 5G environment envisioned for the United States."

Ernesto Falcon, a telecom expert at the Electronic Frontier Foundation, a digital rights group, said air travelers need not worry about 5G interference if the FCC has cleared the matter, because the agency has a proven track record in preventing harmful interference.

Since there's only so much of the radio spectrum to go around, Falcon added, and because demand for those airwaves is at an all-time high, anytime the FCC changes how that scarce resource can be used it tends to provoke a backlash from those who don't benefit from the new system.

"Someone has to call balls and strikes on whether those objections are legitimate or self-serving," Falcon said, and in the United States, that's officially the job of the FCC.

As if to underscore the point, and in an unusual show of force, this month six former FCC chairs, a group that includes both Democrats and Republicans, wrote a joint letter lamenting that the interagency fight over 5G and aviation has unfolded in ways that risk damaging the US government's credibility.

"This debate should not be fought publicly in a way that undermines consumer confidence in the process," the former chairs wrote. "The FAA position threatens to derail the reasoned conclusions reached by the FCC after years of technical analysis and study." (CNN: Excludes headline)

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