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.
John McArthur / Unsplash
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.
Ashim D’Silva / Unsplash
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.
Shandell Venegas / Unsplash
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.
Joe Maring/Digital Trends
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.
Miguel Ángel Sanz / Unsplash
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 po