Federal Register · Regulatory notice

Requirements for Interference-Tolerant Radio Altimeter Systems

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). This final rule supports the Federal Communications Commission's July 2026 Report and Order that makes 160 megahertz of the Upper C-band available for terrestrial wireless flexible use via a system of competitive bidding. To ensure safe, efficient, and reliable aviation operations in the presence of wireless signals in the C-band, the Federal Aviation Administration is issuing new regulations that 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. These regulations 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 December 30, 2030, which is prior to the date the Federal Communications Commission authorizes the use of the Upper C-band for new wireless services, as stated in its Report and Order. All other aircraft equipped with radio altimeters that are required to comply with part 91, including aircraft operating under parts 125, 133, 135, 136, 137, 194, and all other aircraft operating under part 129 that are not subject to the initial deadline, must comply with the same minimum performance requirements on or before October 31, 2034.