The Federal Aviation Administration radio altimeter rule, issued on 24 July 2026 and published in the Federal Register at 91 FR 48656 on 31 July 2026, takes effect on 29 September 2026, requiring all radio altimeters operating in the United States to meet new minimum interference-tolerance standards, according to FreeFlight Systems. The rulemaking lands on the same day the Federal Communications Commission adopted its Report and Order clearing the way for an auction of additional C-band spectrum.
FAA radio altimeter rule sets two compliance deadlines
The FAA’s final rule establishes separate deadlines depending on operator type. Scheduled air carriers, for whom continuity of low-visibility operations is the priority, face the earlier of the two dates. All other aircraft operators are given additional time. The agency did not specify the exact dates in its public statement, though its notice of proposed rulemaking, published on 7 January 2026, had tied the initial deadline to the FCC authorisation date and granted other operators two further years from that point.
The scale of the compliance challenge is substantial. The FAA estimated in that January 2026 NPRM that roughly 58,600 altimeters across approximately 40,900 aircraft would require replacement or upgrade, at an undiscounted cost of $4.49 billion. An industry coalition that included the National Business Aviation Association pushed back in March 2026, telling the agency the real cost could exceed $7 billion. The FAA said the rebate programme established through the FCC order should bring next-generation equipment into commercial fleets several years earlier than would otherwise have been feasible.
Radio altimeters operate in the 4.2 to 4.4 GHz band, directly above the spectrum block being auctioned. They supply height-above-terrain data used during low-visibility takeoffs and landings and feed multiple safety systems, including terrain awareness and warning equipment. Any interference risk in that adjacent band therefore carries direct operational consequences for instrument approaches across the US network.
FCC clears 440 MHz contiguous C-band block with aviation safeguards built in
The Federal Communications Commission voted on 22 July 2026 to adopt a Report and Order covering 160 MHz of Upper C-band spectrum between 3.98 and 4.14 GHz. The commission combined that block with the previously cleared Lower C-band to form a contiguous 440 MHz band. The auction is due to close by July 2027, with new wireless services permitted from December 2030 in the 75 largest US markets and from July 2031 elsewhere.
The FAA said the FCC order incorporates several protections for aviation: limits on the transmit power of auctioned signals, a buffer band separating the new wireless allocation from the altimeter band, and height restrictions on transmission towers using the new spectrum. The agency said years of testing and technical analysis, coordinated with the FCC, underpin its conclusion that aviation can coexist with expanded wireless access on the adjacent frequencies.
The C-band dispute has a recent precedent that coloured negotiations throughout. In 2021, the rollout of Lower C-band services triggered a stand-off between the FAA and wireless operators. The agency issued airworthiness directives restricting certain operations and negotiated buffer zones around 50 US airports with AT&T and Verizon before services could proceed. That episode established the template for the phased, safeguard-heavy approach that both regulators have sought to replicate here.
The rebate mechanism written into the FCC order is funded through auction proceeds, intended to offset retrofit costs for operators facing the new compliance requirements. The FAA framed the incentive as a means of accelerating fleet-wide upgrades, arguing that next-generation altimeters would reach commercial aircraft sooner with financial support than through regulatory mandate alone.
With the FAA radio altimeter rule now effective from 29 September 2026, per FreeFlight Systems, operators and maintenance organisations will need to map their fleets against the new minimum interference-tolerance standards and determine whether existing units qualify or require replacement ahead of their applicable deadline. Details of the Federal Register entry at 91 FR 48656 provide the regulatory text against which compliance assessments will be made, and the FreeFlight Systems summary sets out the key dates and scope for operators working through the process.
