What Is C-Band 5G, and Why Is It Creating Such Controversy in the United States?

In February 2021, C-band spectrum was auctioned off for a total of over US$80 billion in the United States; Verizon spent almost US$50 billion to win the most licenses, followed by AT&T with US$23 billion. Verizon and AT&T have been expanding their 5G coverage since then, but some U.S. airlines and the Federal Aviation Administration (FAA) have raised concerns that 5G services could interfere with aircraft technology—aircraft altimeters in particular—and cause daily flight disruptions of up to 4%. The airlines have requested for the new, faster mobile service to be banned within a two-mile radius of airport runways. On January 18, 2022, Mobile Network Operators (MNOs) Verizon and AT&T agreed again to postpone their 5G rollout near 50 airports to work with the federal regulators in order to settle this dispute over potential interference. In any case, a week after the official pause on C-band rollout for both Verizon and AT&T, the FAA has announced that 90% of aircraft in the United States are cleared to fly.

5G services in the United States use the frequency range of 3.7–3.98 GHz, and aircraft altimeters use the 4.2–4.4 GHz range. Radio altimeters need to provide clear information on an aircraft’s altitude to help with automated landings and to confirm that an aircraft has landed before allowing reverse thrust. Moreover, radio altimeters are highly vulnerable to radio frequency (RF) interference received within the 4.2–4.4 GHz range or by frequency bands that are close by, possibly having a negative impact on their performance. In 2020, the Radio Technical Commission for Aeronautics (RTCA) formed a 5G task force to assess C-band MNO’s impact on low-range radar altimeter operations. The study revealed that 5G systems in the 3.7–3.98 GHz range are a major risk of interference to radar altimeters on all types of civil aircraft, such as commercial transport airlines, transport and general aviation helicopters, and business and general aviation airlines. Without appropriate measures, this issue could result in catastrophic failures and lead to fatalities. The study concluded that the risk cannot be mitigated adequately by the aviation industry alone.

Raised concern about 5G interference has led to increased pressure for these MNOs, and Verizon and AT&T have temporarily suspended their 5G rollouts to investigate this matter with government regulators and to seek potential solutions. While certain 5G deployments in the United States have been put on hold, the MNOs have argued that their equipment will not interfere with aircraft electronics—C-band 5G has been deployed in 40 countries across Asia and Europe, and no aviation interference issues have been raised. Also, 5G in Europe operates in the 3.4–3.8 GHz frequency range; more than 10,000 5G base stations have been built in the past three years, and the European Union Aviation Safety Agency has confirmed that no airports in Europe have experienced problems. 5G in South Korea uses the frequency range of 3.42–3.7 GHz, and no issues have been reported there since 5G was commercialized in April 2019. However, the FAA has noted that the C-band spectrum in other countries are much lower than the 4.2–4.4 GHz range; at the range of 3.7–3.98 GHz, 5G interference seems to be an issue for the United States only.

The pandemic has accelerated the need for 5G networks. U.S. MNOs had been initially focused on mmWave 5G, so they need C-band spectrum to build nationwide coverage 5G networks. The telecommunications sector warns that postponing 5G deployment for one year would cost US$50 billion in economic growth, causing real harm to the United States.

Although 90% of aircraft have been cleared to operate, in the long term, the FAA needs to allow all airplanes in the United States to perform low-visibility landings in airports where C-band 5G will be deployed. 5G and aviation safety can coexist as 5G antennas point to the ground and are equipped with special filters to reduce interference with other systems. The RTCA 5G task force has also stated that the aviation industry needs to make changes to the RF environment for radio altimeter operation and update performance standards to fix the problem. Discussions among the airline industry, federal regulators, and Verizon and AT&T are still ongoing. It is not clear when a definitive path forward will be publicly announced.