TL;DR
The FAA has issued a notice proposing minimum performance standards for aircraft radio altimeters to withstand interference from adjacent mobile services. The agency estimates retrofitting the US fleet would cost $4.49 billion, with a proposed compliance timeline tied to future FCC action on the Upper C‑band.
What happened
The Federal Aviation Administration published a notice of proposed rulemaking that would require radio altimeters to meet defined minimum performance thresholds for resistance to interference from wireless signals in neighboring frequency bands. The move follows a decision in last year’s federal budget process that directed the FCC to free up 3.98–4.2 GHz spectrum (Upper C‑band) for terrestrial wireless use, which sits adjacent to the 4.2–4.4 GHz band used by many aircraft radio altimeters. The FAA says current systems are vulnerable and existing airworthiness directives from 2023 do not fully resolve the risk posed by future Upper C‑band services. It estimates a fleet retrofit bill of $4.49 billion (or $424 million annualized at a 7% discount over 20 years) and proposes aligning the compliance deadline with the FCC’s authorization timeline for Upper C‑band services. The NPRM comment period is open for 60 days, ending March 9.
Why it matters
- Potentially large retrofit costs could affect airline capital planning and operating budgets.
- Radio altimeters provide height data to pilots and safety systems; interference risks could have safety implications.
- Spectrum policy decisions by the federal government are creating direct consequences for aviation hardware and standards.
- Uncertainty about timelines and technical requirements could disrupt coordination between regulators, airlines and wireless operators.
Key facts
- FAA issued a notice of proposed rulemaking requiring radio altimeters to meet minimum interference-tolerance performance.
- Estimated total retrofit cost to the US fleet is $4.49 billion, or $424 million annualized at a 7% discount rate over 20 years.
- The policy follow-up stems from a last year’s budget bill instructing the FCC to auction at least 100 MHz and up to 180 MHz of 3.98–4.2 GHz (Upper C‑band).
- Aircraft radio altimeters operate in the adjacent 4.2–4.4 GHz band, which the FAA says could experience harmful interference from Upper C‑band services.
- FAA judged 2023 airworthiness directives insufficient to address the unsafe condition anticipated from Upper C‑band use.
- Wireless providers have made voluntary mitigation commitments around airports, but those commitments are slated to expire at the start of 2028 unless extended.
- FAA expects a single retrofit of radio altimeters could address compatibility with both Lower and Upper C‑band wireless services.
- The proposed compliance deadline is intended to align with the FCC’s planned authorization of new Upper C‑band services, which the FAA currently expects to occur between 2029 and 2032.
- The NPRM comment window is 60 days and closes on March 9.
- Airline representative groups Airlines for America (A4A) and IATA were contacted for comment; the source has not reported responses.
What to watch next
- NPRM comment window that closes on March 9 (60 days after publication).
- FCC schedule for authorizing new terrestrial services in the Upper C‑band, which the FAA currently anticipates between 2029 and 2032.
- Whether wireless providers extend voluntary mitigation measures beyond their sunset date at the start of 2028.
Quick glossary
- Radio altimeter (RA): An aircraft system that measures altitude above the terrain by sending and receiving radio signals, supplying data to pilots and onboard safety systems.
- Upper C‑band: A portion of the radio spectrum roughly between 3.98 GHz and 4.2 GHz proposed for terrestrial wireless use in this context.
- NPRM (Notice of Proposed Rulemaking): A regulatory document in which an agency proposes new rules and invites public comment before finalizing regulations.
- Airworthiness directive: A legally enforceable notification issued by aviation authorities requiring operators to inspect, repair or modify aircraft to correct unsafe conditions.
- FCC (Federal Communications Commission): The U.S. agency that regulates interstate and international communications by radio, television, wire, satellite and cable.
Reader FAQ
Why is the FAA proposing another altimeter retrofit?
The FAA says future wireless services in the Upper C‑band could interfere with radio altimeters in the adjacent 4.2–4.4 GHz band, and that prior measures do not fully mitigate that risk.
How much will the retrofit cost?
The FAA estimates $4.49 billion in total, or $424 million annualized at a 7% discount rate over 20 years.
When would the new requirements take effect?
The FAA proposes to align compliance with the FCC’s authorization of Upper C‑band services, which it currently expects between 2029 and 2032.
Have U.S. aircraft already been upgraded for past 5G concerns?
The FAA previously said the U.S. fleet had completed upgrades by the end of September 2023 to mitigate earlier 5G-related risks.
Who will pay for the retrofits?
not confirmed in the source
NETWORKS 1 Trump spectrum sale leaves airlines with $4.5bn bill for altimeter do-over Just refreshed to avoid 5G interference? Do it again, FAA tells industry, as Upper C-band auction looms…
Sources
- Trump spectrum sale leaves airlines with $4.5bn bill for altimeter do-over
- Airlines face another altimeter upgrade costing billions
- New radio altimeters to cost US carriers $4.5bn – FAA
- US airlines face $4.5bn radio altimeter upgrade bill due to …
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