It’s been months since Verizon and AT&T got the approval to roll out their 5G C-Band networks to customers. This was done despite some concerns from airplane pilots and the FAA. Now the topic of whether or not 5G frequencies can cause interference with aircraft tools is back in the spotlight.
The FAA monitored service for some time before coming to an agreement with the cellular carriers. In the initial rollout, they agreed that power levels would be limited and exclusion zones created around 50 key airports.
Thankfully, no “catastrophic disruptions” have occurred in the time C-Band service has been in play. Still, several international airlines like Air India suspended their flights to major U.S. airports for the first 48 hours it was available.
It’s probable that the agreed-upon exclusion zones helped mitigate some problems, but the proposed zones didn’t stop aviation officials from voicing concerns and pushing for more delays. The C-band rollout may have been proven to be a non-event, however this doesn’t mean there are not legitimate concerns.
The FCC has been testing back and forth since 2020. This is around the time they had first proposed auctioning off the new spectrum. Their tests allegedly showed 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. FCC’s experts said this 0.22GHz (220MHz) gap would be more than enough to avoid interference.
The FAA disagreed with these findings and referenced a 2020 research paper by the Radio Technical Commission for Aeronautics (RTCA). The RTCA is an independent technology standards group representing the air transportation industry. The study showed that 5G telecommunications in the C-band spectrum could cause “harmful interference” to radar altimeters due to spurious emissions and “bandwidth pollution.”
The study conceded that the frequencies were far enough apart from each other that problems shouldn’t occur. However, 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.
Such interference could cause the radar altimeters in most commercial aircraft to show incorrect readings. This is why the FAA’s list of 5G-excluded airports includes many smaller regional fields that are prone to heavy fog and extended periods of low visibility.
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. A few instances occurred during multiple flights over Tennessee. Pilots experienced altimeter errors that made it impossible to maintain assigned altitude.” Another pilot reported having lost its autopilot completely and another who received errors upon landing at an airport.
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,” an analysis from IEEE Spectrum noted.
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. Regardless, the increasing number of reports has pilots and others within the aviation community spooked.
Fortunately, the National Telecommunications and Information Administration (NTIA), which advises the President on telecommunications and information policy issues, has been working with the Defense Department, mobile carriers, and the aviation industry to continue studying the impact of the new 5G frequencies.
The NTIA reports that there was a “low level of unwanted 5G emissions” in the frequencies used by so-called radar altimeters. To be clear, the report isn’t saying that aircraft instruments are immune from 5G interference. Instead, it confirms that the precautions exercised by the aviation industry and the mobile network operators have been helping.
That being said, we won’t be seeing 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 approval to proceed. That should only happen once all of the potentially impacted radar altimeters have been patched or replaced.
The FAA notes that radio-altimeter manufacturers have been working swiftly to develop and test filters and installation kits for aircrafts. The work will mostly be completed by next July.