Airline CEOs make U-turn, now say 5G isn’t a big problem for altimeters

An airplane cockpit seen during flight.
Enlarge / Airbus 320 cockpit.
Getty Images | Skyhobo

The Federal Aviation Administration’s fight against AT&T’s and Verizon’s new 5G deployment appears to be coming to a temporary close, with the FAA having cleared about 78 percent of US planes for landing in low-visibility conditions. Airline CEOs are striking an upbeat tone, with one saying the process of ensuring that airplane altimeters work in 5G areas is “really not that complicated.”

Over the past week, the FAA announced clearances for 13 altimeters that can filter out 5G transmissions from the C-band spectrum that is licensed to wireless operators, accounting for those used by all Boeing 717, 737, 747, 757, 767, 777, 787, and MD-10/-11 models; all Airbus A300, A310, A319, A320, A330, A340, A350, and A380 models; and some Embraer 170 and 190 regional jets. More approvals will presumably be announced soon, bringing the US closer to 100 percent capacity.

Unfortunately, there could be another showdown in about six months, when AT&T and Verizon lift temporary 5G restrictions around airports—we’ll cover that later in this article. For now, airline CEOs appear to be satisfied, even though the FAA hasn’t said definitively that altimeters will continue working after the temporary 5G limits around airports are lifted.

No “material disruption going forward”

“It’s taken a while to get to the right spot, but I feel like we’re in the right spot,” American Airlines Doug Parker said yesterday, according to a CNN article. “I don’t think you’re going to see any material disruption going forward because of this.”

“While I wish it happened earlier, the good news is we now have everyone engaged, the FAA and DOT at the highest levels, the… aircraft manufacturers, airlines, and the telecoms,” United Airlines CEO Scott Kirby said. “While we don’t have a final resolution quite yet, I’m confident we’ll get there.”

“The technical experts that are working on it tell us it’s really not that complicated once they all are able to share information and work on it,” Parker also said. “So they seem encouraged that we’ll be able to address this in a way that allows for full deployment of 5G, including near airports. I don’t expect until we get to the point that everyone is really comfortable that you’ll see anything turned on near airports, because no one wants to go through this again.”

These statements marked a sudden shift, coming just three days after Parker and Kirby signed a letter claiming that 5G on the C-band would cause “catastrophic disruption” to air travel.

FAA waited almost two years to test altimeters

The biggest recent development is that the FAA finally started a process to evaluate and approve altimeters after claiming without proof that 5G on C-Band spectrum (3.7 to 3.98 GHz) would disrupt altimeters that use spectrum from 4.2 GHz to 4.4 GHz. While the Federal Communications Commission created a 220 MHz guard band to protect airplane equipment, poorly built altimeters may be unable to filter out transmissions from other spectrum bands.

The FAA didn’t start its process of evaluating the actual altimeters used by airplanes after February 2020, when the Federal Communications Commission approved the use of C-Band spectrum for 5G. The FAA also didn’t start this evaluation process after the FCC auctioned off the spectrum to wireless carriers in February 2021. Instead, the FAA continued arguing that 5G deployment should be blocked long after carriers started preparing their equipment and towers to use the C-band.

Harold Feld, a long-time telecom attorney and senior VP of consumer-advocacy group Public Knowledge, told Ars today that the FAA should have started setting up the process to evaluate altimeters shortly after the FCC approved the use of the spectrum for 5G—or, at the very latest, shortly after the $81 billion spectrum auction went forward.

“They spent their time relitigating the whole thing,” Feld said. “It was rash and reckless for the FAA to proceed without any kind of plan B. Had not Secretary [of Transportation Pete] Buttigieg personally intervened and the White House personally intervened and forced the FAA to actually stand this process up, then they still wouldn’t have stood it up on their own.”

FCC deemed C-band safe to use

Nearly two years ago, the FCC found that C-band spectrum was safe to use, in part because T-Mobile showed that airline-industry research did not investigate whether interference would occur in any realistic scenario. Still, the FCC imposed power limits in the 220 MHz guard band—which is actually 400 MHz this year because carriers are not yet deploying on the upper part of their licensed spectrum. C-band spectrum is also being used for 5G in about 40 other countries without reports of interference to altimeters.

“[W]ell-designed equipment should not ordinarily receive any significant interference (let alone harmful interference) given these circumstances,” the FCC said when it approved 5G usage with the 220 MHz guard band. The FCC also pointed out that the 220 MHz guard band “is double the minimum guard band requirement discussed in initial comments by Boeing and ASRC [Aviation Spectrum Resources].”

Fight may not be over

As previously noted, there could be another showdown later this year when AT&T and Verizon lift temporary 5G restrictions around airports. One of the FAA’s statements this week seems to indicate that its approvals for altimeters are good for only as long as those voluntary restrictions are in place. “The new safety buffer announced Tuesday around airports in the 5G deployment further expanded the number of airports available to planes with previously cleared altimeters to perform low-visibility landings,” the FAA said on Wednesday.

If “previously cleared altimeters” can only work properly at airports with the newly announced buffer zone, then the FAA presumably hasn’t determined whether those altimeters will work after carriers deploy C-band 5G without the voluntary limits that go beyond FCC requirements.

We asked the FAA today if this means that the current approvals only apply for as long as the “safety buffer” and other temporary 5G limits are in place and whether new FAA approvals will be needed after temporary restrictions are lifted. The FAA did not answer those questions directly but told Ars, “The buffers around airports reduce 5G signal strengths and allow aircraft to land safely in low-visibility conditions. Prior to these buffers, the signal strength was too strong in certain areas for low-visibility landings to safely occur.”

Although the FAA said nothing about needing to grant new approvals later on, its answer today and the statement on Wednesday suggest that the agency is not ready to declare planes safe to land once temporary 5G limits are lifted.

“Wow. It does appear that we are set for another showdown in early July when the current restrictions are supposed to be lifted,” telecom consultant Tim Farrar told Ars today after we shared the FAA’s response with him. Farrar previously published a blog post analyzing what he called “the FAA’s fearmongering” and slow progress in approving altimeters.

On Twitter, Farrar wrote, “It appears clear from the FAA statements that all [approvals of altimeters] will be invalidated if the 5G deployment restrictions (‘safety buffer’) are removed.”

Feld was disappointed in the FAA’s response to Ars, saying that “it looks very much like a non-answer, which unfortunately has been consistent with everything the FAA has done until now.” The FAA has exhibited “passive-aggressive behavior where it simply refuses to commit to anything until it has its arms twisted” and is “constantly undermining the idea that there is any finality” with “statements that don’t definitively say no,” he said.

Carrier concessions

One of the first major concessions from AT&T and Verizon was to implement “C-band radio exclusion zones” around 50 US airports for six months, until July 5. The carriers also delayed their widespread rollout of C-band spectrum from December 5 to January 19.

The new safety buffer appears to be in addition to the previously agreed-to exclusion zones. “At our sole discretion, we have voluntarily agreed to temporarily defer turning on a limited number of towers around certain airport runways as we continue to work with the aviation industry and the 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,” AT&T told The Hill on Tuesday. AT&T explained further that it had “temporarily deferred turning on C-band transmitters within a two-mile radius of the airport runways specified by the FAA.” The two-mile radius was requested in the letter signed by Parker, Kirby, and other airline CEOs.

It’s not clear whether the safety buffer that carriers agreed to this week will expire on the same six-month timeline. AT&T told Ars today, “We will notify the FAA before any towers are activated within the additional buffer zone announced on Tuesday. We are continuing to engage with the FAA, FCC, and other stakeholders—including providing details about our deployments—to help facilitate the FAA’s technical assessments and clearance of aviation equipment.” We also contacted Verizon today and will update this article if we get more information.

T-Mobile also purchased C-band spectrum licenses at the FCC auction but isn’t deploying on the frequencies until late next year. “We don’t anticipate any limitations when we are ready to deploy it in late 2023,” T-Mobile said.

FAA has more testing to do

At a minimum, the FAA should already be testing altimeters against the levels of 5G transmissions that will occur near airports in July, Feld said. The FAA also needs to verify that altimeters can continue to work properly after AT&T and Verizon deploy in the upper C-band (from 3.8 GHz to 3.98 GHz) in 2023.

“At this point, it isn’t about hypothetical situations with an unknown set of altimeters… You know what the rules are. You know what the altimeters are. You know the date on which we’re going to revert to a different set of rules. How the hell can you not know whether these devices are safe or not under the new rules? The only way you can not know is if you refuse to know,” Feld said.

Feld also said he finds it “increasingly difficult to understand the FAA’s rationale around any of these things, especially given the statements from the [airline] CEOs who actually own and operate this equipment that ‘yeah we’ve done tests, and yeah there’s no problem.'”

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