The U.S. Federal Aviation Administration (FAA) has issued a final rule requiring aircraft radio altimeter systems to meet minimum interference-tolerance performance requirements, part of a coordinated effort to avoid erroneous altitude readings as wireless service expands in spectrum adjacent to the altimeter band.
Where is this coming from?
Radio altimeters (sometimes called radar altimeters) measure an aircraft’s height above the ground and feed that data to pilots and multiple onboard safety systems. The FAA says the upgraded (“next-generation”) altimeters must be able to withstand interference from wireless signals in neighbouring spectrum bands and continue producing accurate readings.
Who must comply, and by when:
- By Dec. 30, 2030: Aircraft operating under Part 121 (scheduled air carriers) and certain Part 129 aircraft (foreign air carriers) with 30+ passenger seats or a payload capacity of over 7,500 pounds.
- By Oct. 31, 2034: All other aircraft with radio altimeters that must comply with Part 91 (including aircraft operating under Parts 125, 133, 135, 136, 137, 194, and other Part 129 aircraft not in the first group).
The FAA also notes the rule has been signed and will be submitted for Federal Register publication and that the “signed” document posted online is not the official Federal Register version (which may include edits).
The FAA ties the rule directly to federal spectrum policy. It says a 2025 law directed the FCC to run competitive bidding for at least 100 MHz in the 3.98–4.2 GHz “Upper C-band” and that the FCC’s July 2026 Report and Order makes 160 MHz available for new terrestrial wireless use, requiring aviation to be ready before those services begin.
Why is radio altimeter interference such a big deal?
In the FAA’s signed final rule document, the agency describes the FCC’s plan in more detail: 3980 to 4140 MHz for terrestrial wireless, a 20 MHz guard band from 4140 to 4160 MHz, and 4160 to 4200 MHz repacked for fixed satellite service while aircraft radio altimeters operate in the adjacent 4.2 to 4.4 GHz band.
In its signed final-rule document, the FAA frames the new performance requirements as applicable to aircraft operating in the 48 contiguous States and the District of Columbia, and it discusses why it is not extending the same requirement to areas where the FCC order does not authorise the new upper C-band base-station environment.
The FAA emphasises that radio altimeters are critical safety equipment, especially for low-visibility takeoffs and landings, and that inaccurate readings can ripple into multiple aircraft safety functions. The agency says its new rule is meant to prevent 5G-adjacent interference that could produce inaccurate altitude readings for pilots and integrated systems.
How do you see C-band 5G expansion panning out?
