5G providers offer C-band proposal to address aircraft interference

Four of the biggest 5G network operators in the US offered a detailed plan for how they might offer C-band network services near almost 200 airports.

The plan comes in response to concerns from the airline industry that 5G transmissions in C-band spectrum might affect aircraft altimeters when used near airports. Such altimeters can be essential to safe aircraft landings in rain and other conditions that can affect visibility.

"These voluntary commitments will support full-power deployments across C-band, and are crafted to minimize the operational impact on our C-band operations. In agreeing to these commitments, we reserve any and all rights and privileges conferred by our lawfully held spectrum licenses issued by the FCC," wrote representatives from Verizon, AT&T, T-Mobile and USCellular in a letter to the FCC.

Officials from the FCC did not immediately comment, according to Reuters. The Federal Aviation Administration (FAA) told the publication that it continues to "work closely to ensure a safe co-existence in the US 5G C-band environment."

A representative from Airlines for America, a trade group representing US airlines including American, Delta and United, offered this statement on the new proposal: "We appreciate the collaboration among stakeholders, including the federal government and will continue to work our common goal of ensuring the aviation system remains the safest mode of transportation in the world. While our industry strongly supports 5G deployment, safety is—and always will be—the top priority of US airlines. A4A member carriers are working diligently to ensure fleets are equipped with compliant radio altimeters, but global supply chains continue to lag behind current demand and any government deadline must consider this reality."

Figure 1: (Source: frans lemmens/Alamy Stock Photo)

In their letter, the 5G operators outlined specific details on how their networks will operate to prevent interference. For example, they said that for all basestations operating at 3.7-3.98GHz, "EIRP [Effective Isotropic Radiated Power] will not exceed 1640 Watts/MHz EIRP (62 dBm/MHz)."

The providers also listed the 188 airports where they will work to prevent interference. The list includes big airports like Denver International Airport, Dallas Love Field, Laguardia Airport and Los Angeles International Airport, along with smaller airports like Albuquerque International Sunport in New Mexico and Bangor International in Maine.

Further, the 5G operators said their efforts will remain in effect for years.

"The commitment will last until January 1, 2028, at which point it will sunset unless extended or reduced by mutual agreement," according to the letter. "A midterm check-in will occur in July 2026 to assess the status of aviation's long-term migration to next-generation radio altimeters and the need for the sustainment of these commitments."

Aircraft retrofitting

Although regulators have contemplated 5G operations in C-band spectrum for years, the airline industry conducted a major public relations push against those transmissions in 2021. After months of back-and-forth, AT&T and Verizon agreed to temporarily curtail their 5G deployments in C-band spectrum around airports to address the airline industry's concerns.

Now, with their latest letter, AT&T, T-Mobile, Verizon and UScellular, which purchased C-band spectrum in an FCC auction in 2021, are essentially agreeing to modify their operations near airports for another six years, until 2028.

Meanwhile, the airline industry is working to upgrade aircraft altimeters so that they don't create interference with 5G operations in C-band spectrum.

"Thales has received around 2,000 orders for its enhanced, 5G immune Radio Altimeters," aircraft vendor Thales noted last year, according to Aviation Today.

However, the aviation industry has argued that upgrading aircraft altimeters is a difficult and time-consuming process.

Broadly, the FCC is working to address the situation with a proceeding into "wireless receiver performance." The agency wants to develop "principles" for receivers like altimeters that would eliminate similar interference situations in the future.

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— Mike Dano, Editorial Director, 5G & Mobile Strategies, Light Reading | @mikeddano