Latest C-Band 5G Delay Allows AT&T, Verizon to Address Aircraft Radar Altimeter Concerns

In statements released Monday, AT&T and Verizon agreed to delay their deployment of C-Band 5G wireless networks by another two weeks in an effort to address concerns over potential signal interference issues raised by U.S. aviation regulators and industry executives in recent years.

The latest delay will move the planned Jan. 5 deployment date of the two 5G C-Band services to Jan. 19, with both AT&T and Verizon also agreeing to adhere to operating their networks in a way that will mitigate potential aircraft radar altimeter issues near airports. AT&T and Verizon on Sunday sent a letter in response, rejecting the request for a further delay made by the Department of Transportation in a letter last week, before committing to the postponement in a new agreement.

“At Secretary Buttigieg’s request, we have voluntarily agreed to one additional two-week delay of our deployment of C-Band 5G services. We also remain committed to the six-month protection zone mitigations we outlined in our letter. We know aviation safety and 5G can co-exist and we are confident further collaboration and technical assessment will allay any issues,” an AT&T spokesperson told Avionics International in an emailed statement.

Aircraft radar altimeters operate within 4.2–4.4 GHz, the lower half of which falls within the C-Band—a frequency range from 3.7–4.2 GHz where the combination of the range of signal transmissions and capacity are optimum. The 5G wireless networks scheduled to be switched on by AT&T and Verizon this month will occur within the 3.7–3.98 GHz frequency range, close to the altimeters, which has left aviation industry experts with concerns over signal interference issues.

On modern commercial and military aircraft, radar altimeters are typically affixed to the bottom of the airframe and transmit radio frequency signals to the ground or terrain. The time that it takes for the signal to reach the ground and reflect back up to the aircraft is measured by the altimeter as its height above ground, updated on a regular basis, multiple times per second. Terrain avoidance and warning systems (TAWS), autoland functionality, and cabin pressurization systems also rely on data supplied by altimeters on the majority of modern air transport aircraft.

Last month, the FAA published new airworthiness directives (ADs) that will prohibit certain types of advanced fixed and rotary wing landing procedures that rely on the use of radar altimeter data. The directives, which would have become effective Jan. 5 under the original one-month delay agreed to by AT&T and Verizon, could be subject to change based on the results of collaboration by the two sides during the new two-week delay period.

As the FAA indicated in its Dec. 7 AD, while it has heard concerns from airlines, the FAA, and aircraft OEMs over the potential interference issues posed by the deployment of 5G in the C-Band, it has not yet been presented with data or information that shows altimeters are not susceptible to interference.

A statement published the FAA on Monday includes a letter documenting some of the terms included in the new deal established between the aviation industry and the two companies. Among the requests outlined by the FAA in the deal include a commitment by AT&T and Verizon to continue to work on establishing several long-term mitigation measures that would address potential interference issues posed by C-Band 5G stations located near airports.

One of the key elements of the deal between the two sides is identifying the geographical locations of C-Band 5G ground stations with a more in-depth understanding provided to the aviation industry regarding how the more powerful beam-forming signals of those stations will function within the C-Band spectrum.

Specifically, the agency is requesting “information on base station locations and operating characteristics planned for Q1 2022,” and that AT&T and Verizon “will continue to work with the FAA in good faith to provide it with complete and accurate information on these locations, to include accurate and complete details regarding expected site implementation dates during the quarter as well as accurate operational characteristics of these locations”…

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