Requirements for Interference-Tolerant Radio Altimeter Systems

[Federal Register Volume 91, Number 4 (Wednesday, January 7, 2026)] [Proposed Rules] [Pages 459-490] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 2026-00051]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 91, 121, and 129

[Docket No.: FAA-2025-5666; Notice No. 26-02] RIN 2120-AM21

Requirements for Interference-Tolerant Radio Altimeter Systems

AGENCY: Federal Aviation Administration (FAA), Department of Transportation (DOT).

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: In July 2025, President Trump signed the One Big Beautiful Bill Act. Section 40002 of that law re-institutes the Federal Communications Commission's general auction authority and specifically directs the Commission to complete a system of competitive bidding for not less than 100 megahertz in the 3.98-4.2 gigahertz band (Upper C- band). To ensure safe, efficient, and reliable aviation operations in the presence of wireless signals in the Upper C-band, the Federal Aviation Administration is proposing new regulations that would require all radio altimeters to meet specific minimum performance requirements. These new radio altimeters must withstand interference from wireless signals in neighboring spectrum bands and continue to provide accurate altitude readings to both pilots and integrated aircraft safety systems. The minimum interference tolerance requirements proposed in this rule reflect the best achievable interference rejection using current technology without compromising radio altimeter system performance. These regulations would require all aircraft equipped with radio altimeters operating under part 121 and those aircraft with radio altimeters operating under part 129 with 30 or more passenger seats or a payload capacity of more than 7,500 pounds to comply with the minimum performance requirements by the date the Federal Communications Commission authorizes wireless services in the Upper C-band. All other aircraft equipped with radio altimeters would be required to comply with the same minimum performance requirements two years later. This proposed rule is a companion to the Federal Communications Commission's NPRM to expand the ecosystem for next-generation wireless services in the 3.7-4.2 gigahertz band by making as much as 180, and at least 100, megahertz of

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the Upper C-band available for terrestrial wireless flexible use via a system of competitive bidding.

DATES: Send comments on or before March 9, 2026.

ADDRESSES: Send comments identified by docket number FAA-2025-5666 using any of the following methods: Federal eRulemaking Portal: Go to www.regulations.gov and follow the online instructions for sending your comments electronically. Mail: Send comments to Docket Operations, M-30; U.S. Department of Transportation (DOT), 1200 New Jersey Avenue SE, Room W12-140, West Building Ground Floor, Washington, DC 20590-0001. Hand Delivery or Courier: Take comments to Docket Operations in Room W12-140 of the West Building Ground Floor at 1200 New Jersey Avenue SE, Washington, DC 20590 between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. Fax: Fax comments to Docket Operations at (202) 493-2251. Privacy: In accordance with 5 U.S.C. 553(c), DOT solicits comments from the public to better inform its rulemaking process. DOT posts these comments, without edit, including any personal information the commenter provides, to www.regulations.gov, as described in the system of records notice (DOT/ALL-14 FDMS), which can be reviewed at www.dot.gov/privacy. Docket: Background documents or comments received may be read at www.regulations.gov at any time. Follow the online instructions for accessing the docket or go to the Docket Operations in Room W12-140 of the West Building Ground Floor at 1200 New Jersey Avenue SE, Washington, DC 20590 between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Mark Fox, Flight Technologies and Procedures Division, AFS-400, Federal Aviation Administration, 6500 S MacArthur Blvd., Building 26, Suite 217, Oklahoma City, OK 73169; telephone (847) 294-7546; email [email protected].