This article is published in Aviation Week & Space Technology and is free to read until Mar 21, 2026. If you want to read more articles from this publication, please click the link to subscribe.
Both U.S. and foreign airlines operating in the country will need more advanced radio altimeters.
The last time wireless telecommunications providers rolled out new services in the previously unused C-Band spectrum, the aviation industry was ill-prepared, and everybody suffered. Telecommunications companies scaled back their offerings while aviation pieced together a set of temporary workarounds to satisfy safety concerns about signal interference with radio altimeters that use adjacent spectrum.
This time around, aviation and wireless stakeholders are prioritizing coordination.
The FAA released a proposed set of minimum performance requirements on Jan. 7 for what it calls “next-generation” radio altimeters (RA) on aircraft that operate in most U.S. airspace. Some 41,000 crewed aircraft that operate within the contiguous U.S. would have to comply with the standards, which in most cases means upgrading onboard equipment.
The FAA is working with wireless stakeholders, led by the Federal Communications Commission (FCC), to develop the standards in advance of the next major wireless services rollout. The FCC plans to auction off up to 180 MHz of upper C-band spectrum between 3.98 and 4.2 GHz by mid-2027. The new RAs must be designed to operate safely around new fifth- and sixth-generation (5G/6G) wireless services planned for the spectrum.
Public comments on the FAA draft rule (Docket No. FAA-2025-5666) are being accepted through March 9. While any rulemaking comment period is relevant, input on the FAA’s proposed standards is seen as a critical part of ensuring the agency’s standards are both satisfactory and reasonable. They also will help guide the FCC’s expansion into the new spectrum.
Among the challenges that both sides face is the rollout’s uncertain timing.
“FAA expects this initial RA performance deadline to be sometime between 2029 and 2032,” the FAA writes in the proposed rule’s preamble, citing the FCC’s best estimates for when new services would be both ready and permitted in the soon-to-be-auctioned spectrum.
Upgrades would come in two waves. Some 27,600 RAs on aircraft designed to hold 30 or more seats operating under Part 121 or Part 129 would need to comply as soon as the new services are in place. Another 31,000 RAs on other aircraft, including some helicopters, would have an additional two years to comply.
The FAA’s plan assumes replacement of RA transceiver units only. While the entire RA system must meet the requirements, retrofitting the transceiver “is expected to solve the spectrum interference issue,” the agency says.
This means existing antennas, designed to meet decades-old interference tolerance requirements that did not include services in adjacent spectrum bands, do not have to be swapped out. The RA modifications are not expected to require substantial wiring rework—another cost- and time-saver.
RTCA and Eurocae are working jointly on a new RA industry standard, which they expect to publish in March 2027. But the FAA has asked the group to fast-track their work and get a standard out by mid-2026, “to align with FAA’s anticipated timeline for publication of a final rule,” the agency said.
Once the standard is out, the FAA will develop new technical standard orders for new RA design and production approvals.
RAs, which operate in the 4.2-4.4-GHz mid-C-band range, are a critical data source. They measure an aircraft’s distance above terrain and obstacles, a function that is vital for ensuring flight safety.
The data also feeds numerous systems that provide automated safety functions, from terrain awareness to collision avoidance. FAA testing has validated that they are prone to interference from signals in nearby bands—a risk that did not exist when the spectrum was set aside for RAs.
The joint RTCA-Eurocae group began its work in 2020—too late to meet the wireless industry’s initial lower C-Band services rollout timeline. That prompted a series of last-minute risk-mitigation steps (AW&ST Feb. 13-26, 2023, p. 60). The FAA issued airworthiness directives (AD) with aircraft-specific operational restrictions, while wireless providers pushed back service launches and voluntarily scaled back deployment plans around nearly 200 airports.
The voluntary restrictions are slated to expire in 2028. Add in the planned new services, and aviation’s need for more resilient RAs is both clear and imminent.
“Existing RA systems are not compatible with this envisioned use, and [ADs] issued by FAA in 2023 are insufficient to address the unsafe condition that will result from wireless services in the upper C-band. In addition, existing RA systems are currently operating with reduced capabilities,” the FAA said. “A single retrofit of RA systems can address long-term compatibility with wireless in both the lower and upper C-band.”
Related Content
