AT&T, Verizon, T-Mobile US and U.S. Cellular are all set to unleash more of their extensive C-band spectrum assets to power their 5G networks that have so far been limited by aviation interference concerns.

The four largest U.S. operators recently filed a letter with the Federal Communications Commission (FCC) stating they would limit the propagation of their cell towers transmitting C-band signals near many airports. This includes 188 larger airports and military bases around the country.

“As C-band licensees, we will abide by the attached voluntary commitments,” representatives from the operators wrote in the filing. “These voluntary commitments will support full-power deployments across C-band and are crafted to minimize the operational impact on our C-band operations.”

The government filing indicates the operators will implement power-reduction capabilities at their radio access network (RAN) towers beaming C-band spectrum near airports. They will also coordinate with the Federal Aviation Authority (FAA) and airport officials on those power limitations for initial deployments, with ongoing monitoring to allow for increased power output where possible.

The move is tied to the proximity of the C-band spectrum to radar altimeters used by some aircraft. The C-band spectrum falls in the 3.7-3.98 GHz bands while the radar altimeters use spectrum in the 4.2-4.4 GHz bands.

However, older radar equipment sometimes operates outside of its assigned bands, which means operators beaming 5G signals near the top-end of the C-band could potentially interfere with the older radar equipment. A similar issue impacted Ligado Networks’ ability to use spectrum it controlled near the 1.5 GHz spectrum band due to potential interference with older GPS equipment.

U.S. operators spent more than $80 billion to gain access to the C-band spectrum licenses to power their 5G network deployments, but has so far been limited in rolling out that spectrum on their RAN equipment near airports due to interference concerns. They have since been working with the FCC and FAA to gain full access to those assets. This includes competing proposals that mostly resulted in contentious language and accusations exchanged between the differing parties.

Despite the geographical limitations, Verizon and AT&T have aggressively moved to boost their 5G coverage using the C-band licenses at thousands of RAN sites. Verizon recently stated its C-band-backed 5G coverage surpassed 200 million potential customers on its way to at least 250 million potential customers covered by the end of 2023, while AT&T surpassed 150 million potential customers covered with C-band at the end of last year.

These two operators have stated they were heading into the tail-end of their capex-heavy C-band deployments, with plans to start lowering those expenses over the next year.

“We’ve got to make our capital dollars stretch a bit further, operationally, with our wireless build, which we are seeing in better than expected C-band coverage performance and our wireless investment last year,” AT&T COO Jeff McElfresh said during a recent investor conference. “All of this goes into our ability to get better return on a lower capital number next year.”

T-Mobile US, which spent just under $10 billion for its C-band licenses, has so far relied heavily on its extensive 2.5 GHz spectrum holdings to power its nationwide 5G coverage.