With a voluntary agreement between wireless carriers and the Federal Aviation Administration set to expire this summer, some members of Congress are worried that the ongoing concerns about potential interference between a new 5G cellphone service and altimeters on some airplanes could disrupt flights and further delay the full rollout of the service.
“We’re seeing passenger travel go up. We know that we have supply chain problems, and I’m very worried that we could be back in a situation for those approximately 5% of airports where 5G has not been turned on near them,” said Sen. Susan Collins, a Republican from Maine, said during an oversight hearing last week.
Collins was referring to a debacle earlier this year in which the wireless industry and the aviation industry publicly clashed over deployment of the newest version of 5G service. On one side were wireless providers eager to activate the high-speed networks for their customers, and on the other were aviation regulators and airlines warning that the signals could interfere with key equipment in airplanes.
Tensions came to a head in January when AT&T and Verizon started turning on that 5G service around the country using newly acquired wireless spectrum in what’s known as the C-band. Concerned that the signals could disrupt aircraft altimeters used for landing in poor visibility, major international airlines, including Emirates, Japan Airlines and ANA, started canceling flights involving Boeing-made planes to several major US airports.
But within days, airlines resumed flights as the FAA began issuing new approvals that allowed almost 80% of commercial airliners to perform low-visibility landings at airports covered by both Verizon’s and AT&T’s rollouts.
The battle, however, may not be over, as US Department of Transportation Secretary Pete Buttigieg told senators last week that the technological fix to address the FAA’s concerns “won’t be completely resolved by this summer” and that it remained a “top concern.”
While he added that the wireless and aviation industries are now working well together to resolve these issues, the public spat revealed just how dysfunctional the coordination efforts among some federal agencies has been in terms of repurposing and getting critical airwaves into use for new 5G communication services. Specifically, the drama between the FAA and the Department of Transportation (which runs the agency) and the wireless industry and its regulator, the Federal Communications Commission, has a long history, which resulted in a high-stakes game of chicken.
There’s a lot at stake. In an FCC auction last year, AT&T and Verizon, the nation’s two largest wireless companies, spent a combined $70 billion to acquire the spectrum needed to roll out their much-hyped 5G services to customers. Though they’ve continually disputed the aviation industry’s predictions that the networks will endanger passenger flights, the carriers twice agreed to delay the network deployments as they negotiated with the DOT and the FAA. Amid the airlines’ threats of massive flight disruptions, AT&T and Verizon announced yet another agreement with the aviation regulator. They would deploy their 5G service but delayed turning on some 5G towers near airport runways.
That voluntary agreement is set to expire in July. The FAA says it is making significant strides to identify planes that may have problematic altimeters and to clear planes that use altimeters with appropriate filters that mitigate interference risk. The agency has put together an interactive map depicting which airports around the country may be affected. The vast majority of airports around the US have 90% or more of their planes cleared for landing in low-visibility approaches.
Buttigieg said it will take time to resolve the issues fully, but he’s confident a solution will be found.
“We are doing everything we can to pursue the technological solutions that I think will be the ultimate long-range fix for this, while in the meantime continuing to pursue and support the negotiated solutions, which I would note have have really worked on a voluntary basis up to now and I think that is a credit to the collaborative spirit that we were able to reach across industries and players,” he said.
AT&T and Verizon echoed Buttigieg’s optimism that the two industries will continue to work together until the technical issues are sorted out without major disruption to air travel or 5G service.
“We continue to work closely and collaboratively with the FAA, and we are encouraged by the progress made thus far. We expect that progress to continue,” said Alex Byers, director of Corporate Communications at AT&T.
Verizon said in a statement that it is “very encouraged by the collaboration and pace in which the FAA, the FCC, and the airline and communications industries have addressed and cleared issues with 5G networks around many airports.”
The company also added that it’s “highly confident that the small and declining number of outstanding questions will be resolved sooner than later, without a significant impact to airline operations or the availability of 5G at airports.”
So how did we get here? This FAQ will explain.
What is 5G again?
5G is the next generation of wireless service, which is built to increase network speeds and make them more responsive. The technology could help make applications like autonomous vehicles a reality and will deliver new AR and VR experiences to smartphones.
Midband spectrum, such as the C-band, is important for 5G deployments because it offers both geographic coverage and the capacity to transmit large amounts of data. This combination is especially appealing to wireless giants that have been trying to fill out their spectrum portfolios.
Why are the airlines worried about interference issues with 5G?
The aviation industry is concerned that wireless carriers’ 5G radios using C-band spectrum will interfere with aircraft altimeters, which are used to measure altitude. Altimeters calculate the distance between an airplane and the ground by transmitting radio frequency signals and measuring the time it takes for those signals to bounce back. Though a malfunctioning altimeter is a big problem anytime during flight, it’s especially dangerous in foggy or hazy conditions when pilots are descending during approach and can’t clearly see a runway. A crash could result, which is at the core of the FAA’s worry.
The problem is that altimeter receivers operate in the 4.2GHz to 4.4GHz range on the radio frequency spectrum. The C-band of spectrum that the wireless industry is using to deploy 5G service is between 3.7GHz and 3.98GHz, which is basically next door.
Did the FCC do anything to mitigate interference with altimeters or anything else?
Yes, because the agency regulates the nation’s airwaves. Interference is a common problem whenever spectrum is reallocated, but the FCC and other wireless experts say there are ways to ensure coexistence between applications using spectrum in close proximity. For example, filters on altimeter receivers could reduce the interfering “noise” from the 5G signals emanating from towers near airports.
To help reduce the chance for interference between 5G users on C-band and altimeters, the FCC allocated a large guard band of 220MHz where no one would transmit signals, a significant buffer. The FCC had actually doubled that guard band from what Boeing had originally requested in its filing to the agency during the public comment period, and the FCC’s engineers concluded the guard band was sufficient.
So what’s the problem? Why are the FAA and the airlines still worried?
The aviation industry and the FAA cite a report from October 2020 that concluded even with the guard band, there was possible harmful interference. The agency contends that the FCC has ignored its concerns about interference. Now that the spectrum is being deployed, the FAA believes the possibility of interference poses too great a risk to the public, which is why it has issued warnings and restrictions.
What does the FCC say about these interference issues?
The FCC says it hasn’t ignored these concerns. It just disagrees with the FAA’s conclusions. It has reiterated that after years of study, its engineers believe there’s no meaningful interference between 5G devices operating in C-band and aircraft systems.
In a statement on Jan. 18, FCC chairwoman Jessica Rosenworcel said she is confident that 5G “deployment can safely co-exist with aviation technologies in the United States, just as it does in other countries around the world.”
What about the wireless carriers? What’s their reaction been?
The wireless industry trade group CTIA and the carriers themselves expressed frustration early on in the conflict with the FAA and the aviation industry. They stand with the FCC and point to the fact that roughly 40 countries have deployed the C-band spectrum for 5G without reports of harmful interference with aviation equipment. Japan, the home country of both JAL and ANA, is one of them.
AT&T CEO John Stankey and Verizon CEO Hans Vestberg said in a letter to Buttigieg and FAA Administrator Steve Dickson in early January that the concerns are overblown.
“The laws of physics are the same in the United States and France,” they said. “If US airlines are permitted to operate flights every day in France, then the same operating conditions should allow them to do so in the United States.”
Still, AT&T and Verizon reluctantly made concessions. In November, they agreed to delay deployment of 5G until early January, allowing more time to the FAA to test altimeters. They also offered to reduce the power levels on their 5G radios around airports.
When the FAA said it still needed more time on the eve of the 5G launch in early January, they agreed to another two-week delay, to Jan. 19. At that time, they also agreed to put in place 5G exclusion zones within 1.5 miles of airports, which is the same standard used in France, where similar spectrum is deployed for 5G.
But it was clear at the time that the carriers were unhappy about the situation. They felt the DOT, FAA and aviation industry were being unreasonable.
Why did airlines start canceling flights? What happened to the earlier agreement?
Days before the carriers were set to deploy their networks, the FAA put out a notice stating that only 45% of the aircraft used by US airlines had been cleared to fly. This meant that for the remaining 55% it was unknown whether 5G interference would be a problem.
As a result, airlines began canceling flights for airliners that weren’t part of the FAA’s initial clearance list. The airlines stated they couldn’t fly their planes if there was a chance of a catastrophic accident.
Which airplanes were initially deemed to be problematic and why?
The airlines canceled flights that used a variant of the Boeing 777. It has a radio altimeter that was thought to be particularly susceptible. A long-haul, high-capacity plane, the 777 is popular with airlines both in the US (like American and United) and around the world. Also affected was the Boeing 747-8, which flies largely with cargo airlines. But following an FAA update, the two aircraft were cleared.
A new deal was struck. What’s in the new agreement?
Verizon and AT&T went ahead with their deployment, as planned. But they agreed to enlarge the exclusion zones to two miles around certain airports for six months. This is the agreement set to expire in July. By expanding the exclusion, they have turned down the power or turned off transmission of 5G radio signals on the C-band spectrum in these areas around key airports.
Meanwhile, the FAA has continued its work to test altimeters. The agency has put together an interactive map where the public can check which planes have been cleared and what airports may still be affected by the issues.
Why did the FAA and aviation industry wait until just before 5G service on this spectrum was launched, to make these concerns public?
They didn’t, says Diana Furchtgott-Roth, a former deputy secretary at the Department of Transportation, who has worked on spectrum issues. She said the DOT, FAA and industry have been vocal about their concerns for more than a year.
She pointed to a letter the DOT and the FAA sent in December 2020 before the C-band auction to the National Telecommunications and Information Administration, the government agency tasked with being the go-between for government agencies and the FCC on spectrum issues, expressing their concern of interference. They wanted to ensure that their comments were part of the FCC’s public record on reallocating the C-band spectrum.
But Furchtgott-Roth said NTIA never submitted that letter to the FCC. Meanwhile, 12 aviation trade groups, including the Aerospace Industries Association and the Aircraft Owners and Pilots Association, filed concerns with the FCC to halt the C-band auction amid interference concerns.
Furchtgott-Roth said that a letter from another federal agency would have held more weight in terms of the public record had it been filed.
“It would have been a signal to these wireless companies that there was something problematic with the spectrum,” she said. “And they might have altered their bids for the spectrum.”
How does this whole debacle impact wireless consumers?
AT&T and Verizon have been deploying 5G using the C-band spectrum largely as they had planned. But until the voluntary agreement expires this summer, 5G signals using this spectrum will be diminished within the two-mile exclusion zones around airports. That means that anyone living in areas close to these airports or passengers waiting for flights will either not have access to this 5G service or it will be greatly diminished in performance or capacity.
It’s unclear exactly how many consumers have been affected. Some airports don’t have residential areas within the two-mile exclusion zone, while others, like LaGuardia in New York City, likely have thousands of homes nearby.
This is a situation where the wireless carriers are taking their cues from the FAA and not the FCC. How unusual is this?
This is highly unusual. It could signal bigger problems down the road, as the FCC looks to free up more spectrum for commercial use.
What’s next? What’s the long-term fix to this issue?
A number of things still need to be done in order to resolve this issue once and for all.
- The aviation industry and the FAA need to identify which altimeters are vulnerable to interference. The FAA is already working on this.
- Once problematic altimeters are identified, there needs to be a process to change them or add filters so that they’re no longer vulnerable to interference from 5G signals.
There needs to be a set of standards for altimeters going forward so that any new devices have the proper filtering technology so they can coexist with 5G signals.
All of this requires continued collaboration among the wireless and aviation industries and their regulators. That is already starting to happen. In February, the FCC and the National Telecommunications and Information Administration or NTIA, which helps coordinate the use of spectrum among federal agencies, announced a new initiative to “address gaps” in how they manage spectrum allocation. As part of the effort, the agencies will update a memorandum of understanding on spectrum duties.
“Now more than ever we need a whole-of-government approach to spectrum policy,” the FCC’s Rosenworcel said earlier this year “Over the past few years, we’ve seen the cost of not having one, and we need a nonstop effort to fix that.”
But at the end of the day, Furchtgott-Roth said, the American public should be grateful the FAA has remained vigilant.
“It might be a mess, but passengers are going to be safe,” she said. “No one has to be afraid of flying, because the FAA always errs on the side of safety. They’re simply not going to let a plane land or take off unless they’re absolutely sure it’s safe.”