Verizon and AT&T face a new level of uncertainty after the operators begrudgingly volunteered to delay the commercial launch of 5G service on C-band spectrum they licensed for a combined $68.9 billion.

Outstanding concerns about the recently auctioned mid-band spectrum's potential to interfere with aviation equipment puts both operators in a bind. There's no guarantee the one-month delay, which pushes back initial 5G network activations to the first week of January 2022, won't be extended further into next year. 

Spectrum interference remains a constant point of debate and concern impacting the wireless network space, but this near-the-finish-line delay after years of studies poses significant harm to AT&T and Verizon's 5G network expansion plans.

The U.S trade association CTIA blasted this latest wave of concern in a filing with the Federal Communications Commission (FCC), which first sought comment on making the C-band available to mobile operators in 2017. 

Representatives of the aviation industry are using "flawed analysis" to "argue that 5G operations in the C-band will cause harmful interference to radio altimeters that operate up to 500 megahertz away," CTIA wrote in the filing.

The spectrum licensed primarily by the big three U.S. operators for mid-band 5G service falls in the 3.7-3.98 GHz band and radar altimeters used by aviators operate between 4.2 GHz and 4.4 GHz.

The lobbying group also notes operators in nearly 40 countries have deployed hundreds of thousands of base stations running in the C-band and "none of these countries has reported any harmful interference with aviation equipment from these commercial deployments."

The Federal Aviation Administration (FAA), National Telecommunications and Information Administration (NTIA), and FCC are all looking into the matter. The FAA specifically asked radio altimeter manufacturers, operators, and aircraft makers to provide details about altimeter design, functionality, deployment and usage in aircraft with a voluntary request to test and assess their equipment with federal authorities.

This effort includes the testing and analysis of each model number in production or still in use, and an approximate tally of each radio altimeter model installed on every aircraft in service in the U.S. That doesn’t sound like something that can be accomplished in a month. 

AT&T and Verizon agreed to the delay two days after the FAA issued an ominous bulletin warning aviators that “action might be required to address potential interference with sensitive aircraft electronics.” Radar altimeters measure how close an aircraft is to the ground, a critical reading that helps pilots land safely. 

“There have not yet been proven reports of harmful interference due to wireless broadband operations internationally, although this issue is continuing to be studied,” the FAA wrote in the bulletin. 

The latest snafu dates back to October 2020 when the Radio Technical Commission for Aeronautics (RTCA), a non-governmental organization that studies aviation technology, issued a report warning that radio interference could negatively impact tens of thousands of civil aircraft in the U.S. and worldwide. 

“Radar altimeters are the only sensor onboard a civil aircraft which provides a direct measurement of the clearance height of the aircraft over the terrain or other obstacles, and failures of these sensors can therefore lead to incidents with catastrophic results resulting in multiple fatalities,” RTCA wrote in the report.

The group pleaded with the FCC to conduct further study, but CTIA claims these concerns are unfounded, adding the “RTCA report shows harmful interference on paper where no such interference exists in the real world.” 

A group of major airline companies also banded together in August and cited the RTCA report to issue a warning, claiming major disruptions on air travel can be expected from the rollout of 5G service on C-band spectrum. 

AT&T and Verizon are playing it cool publicly, but tens of billions of dollars and their respective competitive stance in the 5G era hang in the balance. “It is critical that these discussions be informed by the science and the data,” AT&T said in a statement.

Both operators thus far appear confident that delays won’t extend beyond early January, and construction activities related to mid-band 5G deployments are likely continuing as planned. 

Verizon previously pledged to cover 100 million people with mid-band 5G in 46 markets by March 2022, and CEO Hans Vestberg last month said the operator is on track to meet that goal. AT&T, following a shedding of misbegotten media assets, effectively doubled its mid-band 5G deployment plans to reach 200 million people by the end of 2023.

Meanwhile, T-Mobile US remains far out in the lead with a mid-band 5G network riding on 2.5 GHz spectrum it acquired in its purchase of Sprint that currently covers 190 million people. CEO Mike Sievert last week claimed T-Mobile has a two-year lead on its competitors in 5G, and the latest C-band delay for AT&T and Verizon pushes that lead a little further in T-Mobile’s favor.