UPDATE The FAA has finalized its policy for demonstrating aviation radio altimeters can operate in areas where 5G C-band signals are transmitted without fear of interference. The agency rejected calls for substantial changes and one request to withdraw the proposed standards. The process has been on-going for a year. The final policy is due to be released in the coming days, according to a Federal Register notice.
Few changes were made to a draft document released in May, reports Aviation Week. Among its clarifications: data submitted for alternative methods of compliance approvals prior to the draft policy must be re-submitted.
“Design approval holders or operators will need to provide the FAA with data showing explicitly that the aircraft meets the tolerances,” the agency said. The “FAA does not maintain a list of tolerant radio altimeters; the determination of a radio altimeter tolerant aircraft must consider the installation details, which vary from aircraft to aircraft,” it added. The agency also said the final policy includes “guidance … to assist with obtaining FAA approval expeditiously.”
Trade group Airlines For America wanted the policy withdrawn, citing operators’ lack of control over what design approval holders have submitted to the FAA and the (then) pending deadline of July 1. FAA said the policy is needed to support the latest directives issued to prevent aircraft from encountering interference from 5G C-band deployments being rolled out by wireless telecoms.
Operators, manufacturers, and affected radio altimeter providers have been working to ensure their aircraft are “tolerant” in the new 5G environments for more than a year, notes Aviation Week. A phased plan created as a result of discussions between the FAA, FCC, the aviation industry and the carriers called for aircraft to be cleared or modified with filters by July 1 to align with carriers’ plans to fully deploy their 5G networks near airports, Inside Towers reported.
U.S. carriers had cleared about 80 percent of their aircraft by late June, according to information provided to the U.S. Transportation Department. Airlines and manufacturers have cited supply chain issues and the challenge of developing upgraded equipment as primary hurdles.
Aircraft not cleared to operate in 5G environments face restrictions when operating in low-visibility weather. In addition, some systems that rely on radio altimeter data may be restricted.
Radio altimeters calculate the precise distance between an aircraft and the ground and use the 4.2-4.4 GHz frequency band. The FCC authorized carriers to use 5G C-band frequencies on 3.7-3.98 GHz.
The 5G services using similar C-band spectrum are in place around the world with no reports of interference with aircraft, Inside Towers reported. But the agency is concerned that differences in the U.S. networks, including power settings on transmitters and antenna angles, introduce risk.
The final policy, “Demonstration of Radio Altimeter Tolerant Aircraft, Policy No. PS-AIR-600-39-01,” will be available in FAA’s Dynamic Regulatory System (drs.faa.gov) and in docket no. FAA-2023-0938.
By Leslie Stimson, Inside Towers Washington Bureau Chief
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