After months of wrangling with the aviation industry, AT&T and Verizon finally got the green light to go live with their new C-Band 5G rollouts earlier this year. While both carriers had to make some concessions to placate fears that the new spectrum would interfere with aircraft instruments, some pilots are now wondering if those were enough.
Throughout most of 2021, the Federal Aviation Administration (FAA) and key aviation industry stakeholders argued that the frequencies used by the new C-band spectrum sat perilously close to those occupied by critical aircraft instruments, such as radar altimeters. The Federal Communications Commission (FCC), AT&T, and Verizon disagreed — citing studies conducted by the government regulator that showed little to no risk.
Nevertheless, the carriers agreed to delay their planned December 2021 rollouts to January 5 to provide more time to review the concerns and study the potential impact on aircraft. However, when the FAA pushed for an extension to that, the White House got involved to broker a quick agreement between all the parties involved.
In the end, AT&T and Verizon were cleared to switch on their C-band networks on January 19, with the proviso that they would limit C-band 5G power levels and agree to exclusion zones around 50 key airports for the initial rollout.
No ‘catastrophic disruptions’
Despite dire warnings from some quarters of the aviation industry, the rollout of the new C-band spectrum moved forward without any of the “catastrophic disruptions” predicted by airline executives.
In fact, the only disruptions that occurred were largely self-inflicted. Several foreign carriers, including Japan Airlines and Air India, suspended their flights to major U.S. airports. At the same time, the CEO of Emirates additionally told CNN that the 5G rollout was “one of the most delinquent, utterly irresponsible” things he has seen in his aviation career.
Nevertheless, flights resumed less than 48 hours after the C-band rollout began, and since then, the aviation industry seems to have quietly taken the rollout of the new 5G frequencies in stride.
While it’s fair to say that the agreed-upon exclusion zones around major airports helped mitigate some of the problems, the proposed zones didn’t stop aviation officials from sounding alarm bells and pushing for more delays. It wasn’t until after the C-band rollout proved to be a non-event that officials quietly agreed that perhaps it wasn’t nearly as significant of a problem as they first feared.
5G and radar altimeters
While the C-band rollout hasn’t created any catastrophic safety problems for the airlines, this doesn’t mean that aviation industry officials and researchers don’t have legitimate concerns.
The potential does exist for interference between the new 5G spectrum and the frequencies used by aircraft instruments. It’s an issue that’s been studied back and forth since at least 2020 when the FCC first proposed auctioning off the new spectrum.
The FCC insisted its tests had shown that the new C-band spectrum, which operates in the 3.7–3.98GHz range, was far enough away from the 4.2–4.4GHz frequencies used by radar altimeters. The FCC’s experts said this 0.22GHz (220MHz) gap would be more than enough to avoid interference.
However, the FAA disagreed, citing a 2020 research paper by the Radio Technical Commission for Aeronautics (RTCA), an independent technology standards group representing the air transportation industry. This study showed that 5G telecommunications in the C-band spectrum could cause “harmful interference” to radar altimeters due to spurious emissions and “bandwidth pollution.”
Although the study conceded that the frequencies were far enough apart from each other that problems shouldn’t occur, the issue was that increased 5G usage was likely to result in a strong enough concentration of signals that they could “bleed through” into neighboring frequency bands in the same way that light pollution happens in the vicinity of major cities.
Such interference could cause the radar altimeters in most commercial aircraft to show incorrect readings, which could be fatal in situations where pilots rely on accuracy to negotiate landings in difficult weather conditions. That’s why the FAA’s list of 5G-excluded airports includes many smaller regional fields prone to heavy fog and extended periods of low visibility.
Pilots reporting concerns
Although there have been no public reports of serious safety issues, the 5G rollout left some pilots rattled after they experienced problems with radar altimeters that they believe are linked to the new C-band frequencies.
According to a recent report by IEEE Spectrum, complaints about altimeter failures rose significantly following the January 19 deployment of the new C-band spectrum. Of course, correlation doesn’t always equal causation, and the controversy over the 5G rollouts brought a certain level of hyper-awareness among aircraft crews. Still, there have been enough reports to suggest some link between the two.
For example, shortly after the C-band deployments began, multiple flights over Tennessee began experiencing altimeter errors that made it “impossible to maintain assigned altitude,” according to a pilot report made to NASA’s Aviation Safety Reporting System (ASRS). One airliner reported losing its autopilot completely, raising enough concerns that ground control had fire trucks waiting for it on landing.
Another report in February revealed that a passenger aircraft on approach for a landing at the Louis Armstrong International Airport in New Orleans received erratic low-altitude warnings. While these didn’t present a direct safety concern, the pilot noted that they could be “extremely distracting in a more challenging environment such as low visibility, icing conditions, etc.”
A commercial jet experienced a potentially more severe autopilot failure in March at Los Angeles International Airport, going into an “aggressive” descent just 100 feet above the ground — a scenario that could have caused a crash had the pilot not taken manual control of the aircraft.
To be clear, these kinds of problems weren’t unheard of before the rollout of 5G; that’s why pilots have always been required to be strapped into their seats and ready to take control at a moment’s notice when an aircraft is operating on autopilot. However, the increasing frequency of such reports is causing concern among many folks in the aviation industry.
According to IEEE Spectrum, which analyzed reports made to the ASRS database, “complaints of malfunctioning and failing altimeters soared after the rollout earlier this year of high-speed 5G wireless networks.”
Specifically, 93 reports related to radar altimeter problems were filed between January and May this year. “January alone saw almost twice as many complaints of malfunctioning altimeters as the previous five years combined,” the analysis noted.
In many cases, the aircrew member making the report pointed to 5G interference as the cause. Of course, this is pure speculation, but it shows how much the new 5G deployments have been at the forefront of aviators’ minds.
One pilot who was making a flight to San Francisco after the new 5G frequencies went live reported their plane’s speed brakes unexpectedly activating before touchdown. “With over 18,000 hours as Captain of Boeing airliners…I’ve never had the auto speedbrakes deploy uncommanded before ground contact,” the pilot wrote in the report, adding that “While I operate in the 5G environment, I have no intention of being the first to make a 5G landing.”
However, some experts believe that all the hype around the perils of the new 5G spectrum could skew the perceptions of folks in the cockpit. IEEE Spectrum spoke with Chris Rudell, an associate professor in the department of electrical and computer engineering at the University of Washington, who suggested that at least some pilots may be misinterpreting what they’re experiencing in light of all the hype.
“I’d sleep like a baby [on a plane] that flew over a 5G base station at full power output,” Rudell told IEEE Spectrum, adding that pilots are much more likely to attribute instrument failures to the 5G rollouts, even in situations where there’s no obvious connection. It also doesn’t help that the FAA has added a specific online form for reporting radio-altimeter anomalies in the wake of the new C-band rollouts, encouraging pilots to report incidents they may have previously shrugged off.
The FAA told IEEE Spectrum that it has received around 550 submissions since January, although it’s only investigated about half of them so far. The agency couldn’t rule out 5G interference in about 80 reported incidents. However, it was quick to add that none of those incidents that could have been caused by 5G had any impact on systems related to aircraft safety.
The light at the end of the tunnel
Since bandwidth pollution is caused by stronger concentrations of frequencies, officials can’t assume that more problems won’t occur in the future merely because things have been going relatively smoothly so far.
As more people upgrade to 5G devices, carriers put up more C-band towers, and 5G usage in those frequencies increases, certain areas may reach a critical threshold of 5G signals that could be enough to interfere with aircraft instruments.
Fortunately, researchers and regulators aren’t standing still. As Bloomberg recently reported, the National Telecommunications and Information Administration (NTIA), which advises the President on telecommunications and information policy issues, has been working with the Defence Department, mobile carriers, and the aviation industry to continue studying the impact of the new 5G frequencies.
The results have been promising, showing that while airline equipment is still potentially at risk from 5G interference, the mitigations that have been put in place appear to be working. This includes the exclusion zones and lower power levels used by carriers, along with radio frequency filter “patches” mandated by the FAA for “radio altimeters most susceptible to interference.” Verizon and AT&T have also agreed to continue with some level of voluntary mitigations until at least the middle of 2023
The NTIA report noted that there was a “low level of unwanted 5G emissions” in the frequencies used by so-called radar altimeters, so the report isn’t saying that aircraft instruments are immune from 5G interference; it merely confirms that the precautions exercised by the aviation industry and the mobile network operators have been paying off.
In other words, don’t expect to see Verizon’s Ultra Wideband or AT&T’s 5G Plus network at major airports anytime soon. Since these higher-tier 5G services mostly use the C-band spectrum, the carriers have to wait until the FAA has given them the green light to proceed, which will only happen once all of the potentially impacted radar altimeters have been patched or replaced.
The FAA notes that “radio-altimeter manufacturers have worked at an unprecedented pace to develop and test filters and installation kits for these aircraft” that “can be installed in a few hours at airline maintenance facilities.” The regulator expects the work to be mostly completed by next July, after which it expects that “the wireless companies expect to operate their networks in urban areas with minimal restrictions.”
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