Safety

Radio altimeters and 5G in 2026: the upper C-band auction and the next retrofit

August 13, 2026Updated September 30, 202610 min readFor pilots

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In this article

The 2022-2024 fix in brief
Why the upper C-band is different
What the FCC and FAA decided
Where the two sides stand
The new industry standard
Outside the United States
What an anomaly looks like
What depends on the RA
What it means for pilots

The 5G and radio altimeter story looked settled in 2024. U.S. airliners had tolerant radio altimeters or filters, and the wireless carriers were holding power down near airports. It is open again. In 2025 Congress ordered the FCC to auction spectrum even closer to the radio altimeter band, and in July 2026 the FAA answered with a rule that requires a new generation of radio altimeters on every U.S. airliner by the end of 2030. The rule and most of the FCC order took effect on September 29, 2026. Here is how we got here, what each side argued, and what it means on the flight deck.

The 2022-2024 fix in brief

Radio altimeters work in 4.2-4.4 GHz. In early 2020 the FCC opened 3.7-3.98 GHz, the lower C-band, to high-power wireless service, and completed the auction in February 2021. SAFO 21007 noted the gap between the two bands was 220 MHz. The FAA's position was that a radio altimeter has to pick out a faint signal reflected from the ground, and many existing designs could not reject strong signals that close.

The FAA's first answer was AD 2021-23-12 (December 2021), which put limits in the AFM on operations that need radio altimeter data, switched on by NOTAM where 5G was active. 5G C-band service launched in 46 markets on January 19, 2022, after AT&T and Verizon agreed to a short delay and to buffer zones around 50 airports that the FAA listed on January 7, 2022.

AD 2023-10-02, published May 26, 2023, replaced the NOTAM approach. After June 30, 2023, airplanes that were not radio altimeter tolerant carried the low-visibility limits everywhere in the contiguous U.S., and as of February 1, 2024, an airplane had to be tolerant to fly under Part 121 there. Operators met it with new or modified radio altimeters or external filters. The FAA estimated about 1,000 U.S.-registered airplanes still needed work, roughly 180 by replacing radio altimeters and 820 by adding filters. The FAA says the U.S. airline fleet had finished its upgrades by the end of September 2023.

The carriers' side of the deal was voluntary. Before July 1, 2023, Verizon, AT&T and 19 other lower C-band licensees committed to coordinate power levels and limit emissions into the radio altimeter band until January 1, 2028. The FCC order notes that since 2023 they have held spurious emissions into 4.2-4.4 GHz to a conducted -48 dBm/MHz.

Why the upper C-band is different

Section 40002 of the One Big Beautiful Bill Act (Public Law 119-21, signed July 4, 2025) restored the FCC's auction authority through September 30, 2034. It requires auctions of at least 300 MHz, including completing an auction of "not less than 100 megahertz in the band between 3.98 gigahertz and 4.2 gigahertz" within two years, which means by July 4, 2027.

The FCC went beyond the minimum. Its Report and Order (FCC 26-46), adopted July 22, 2026, repurposes 160 MHz:

Band	Use after the transition
3.70-3.98 GHz	Lower C-band 5G, in service since 2022
3.98-4.14 GHz	Upper C-band, to be auctioned for terrestrial wireless
4.14-4.16 GHz	Guard band
4.16-4.20 GHz	Satellite service, repacked
4.20-4.40 GHz	Radio altimeters

The gap between wireless service and the radio altimeter band shrinks from 220 MHz to 60 MHz. The FAA's final rule states that the radio altimeters installed today cannot withstand the new upper C-band signals, and cannot withstand lower C-band signals at the FCC's original limits once the voluntary commitments end.

What the FCC and FAA decided

The two agencies published companion rules on July 31, 2026, and aligned the dates.

The FCC order

Base station antennas are limited to 450 feet AGL. Out-of-band emissions into 4.2-4.4 GHz must stay at or below -28.4 dBm/MHz EIRP or -46 dBm/MHz conducted power, a limit the FCC also applies to the lower C-band. New upper C-band service may start on December 31, 2030 in the top 75 markets (Partial Economic Areas), about 70% of the U.S. population, and by July 1, 2031 everywhere else in the contiguous U.S. Alaska, Hawaii and the territories are not included. Auction 115 is scheduled for April 27, 2027.

Winning bidders must fund rebates for radio altimeter retrofits on U.S. aircraft. The FCC estimates total rebates at $3.83 to $5.71 billion, with about $2.21 billion for aircraft under the first FAA deadline and a cap of $3.5 billion for the rest. Foreign-registered aircraft are not eligible.

The FAA rule

The rule (Docket FAA-2025-5666) sets an Interference Tolerance Mask, which defines how much interference a radio altimeter must tolerate at each frequency. It does not require a specific industry standard. Compliance dates:

December 30, 2030: Part 121 aircraft, and Part 129 aircraft with 30 or more passenger seats or more than 7,500 pounds payload (new sections 121.326 and 129.16(a)).
October 31, 2034: all other radio altimeter-equipped aircraft under Part 91, including Parts 125, 133, 135, 136, 137 and 194, and the remaining Part 129 aircraft (91.220 and 129.16(b)).

The FAA counts about 58,514 radio altimeters on 40,730 civil aircraft and puts the cost for airplanes at $80,000 to $120,000 per radio altimeter, installed. The FCC, citing the FAA, puts the Part 121 fleet at 8,662 aircraft with 18,423 radio altimeters. The FAA plans to ask Part 121 and 129 operators to submit equipage plans by the end of 2026.

On the lower C-band, AT&T, T-Mobile and Verizon told the FCC in June 2026 they "are prepared to extend the voluntary commitments until the FCC's initial date for licensees' access to Upper C-Band spectrum." Both agencies now treat December 2030 as the end of those commitments.

Where the two sides stand

Nearly every commenter, aviation and wireless, supported new radio altimeter performance requirements. The disagreements were about timing and cost.

A joint aviation filing of February 18, 2026, from 23 organizations calling themselves the Joint Aviation Community, including A4A, ALPA, AOPA, Boeing, GAMA, IATA, NBAA and RAA, asked for a "one-and-done" retrofit and projected airline completion by mid-2032 and the rest of the fleet by 2034. In March 2026, A4A, Boeing, Airbus, Embraer, the RAA, Collins, Honeywell and Thales sent the FCC a faster timeline: with rebates to pay for the work, most in-service retrofits could be done during overnight maintenance by the end of 2029, and the regional aircraft that need a newly designed transceiver by the third quarter of 2030. In comments to the FAA, the Joint Aviation Community pointed out that many aircraft already went through one retrofit, at the operators' expense, for the lower C-band and now face a second. A4A called the voluntary commitments the primary mitigation for legacy radio altimeters until new equipment is in service. ATR proposed deadlines of 2036 and 2038.

On the wireless side, CTIA urged a 2029 deadline and argued that the cost of any missed aviation deadline should fall on aircraft operators, not wireless licensees. The Competitive Carriers Association said it was unacceptable to put the burden of aviation's delay on the carriers. Wireless interests argued that the FCC's Emerging Technologies framework, which aviation groups cited as the basis for rebates, was unsuitable for radio altimeter upgrades. The FCC adopted CTIA's proposed emission limit into the radio altimeter band.

The FAA held to December 30, 2030. For the rare aircraft that still miss it, the Administrator can authorize continued operation, but with the same limits the ADs impose: no CAT II/III, SA CAT I/II, autoland, HUD to touchdown or EFVS to touchdown.

The new industry standard

RTCA SC-239 and EUROCAE WG-119 are writing a new radio altimeter MOPS together. RTCA said in February 2025 that it planned final review and comment by September 2026 and publication by March 2027. The FAA confirms March 2027. EASA urged the FAA to wait until the MOPS were validated and warned that meeting only the FAA's mask could mean another retrofit if other authorities adopt the full standard. The FAA did not wait, saying the suppliers doing the validation work supported its mask below 500 feet.

Outside the United States

Canada

Canada has relaxed the airport protections its spectrum regulator, ISED, set in 2023. Exclusion and protection zones at airports ended July 1, 2026, and the FAA says what remains protects only tolerant airplanes. FAA AD 2026-13-02, effective July 1, 2026, bars non-tolerant airplanes from CAT II/III, SA CAT I/II, autoland, HUD to touchdown and EFVS to touchdown in Canadian airspace, and requires Part 121 airplanes there to be tolerant. An airplane tolerant under AD 2023-10-02 counts. Under a voluntary agreement described in Transport Canada CASA 2026-08, Canadian wireless carriers keep some limits, including a -42 dBm/MHz spurious limit into 4.2-4.4 GHz, until December 31, 2027.

Europe

EASA SIB 2026-03 (April 14, 2026) reports erroneous radio altimeter indications on ERJ-145 and E-Jets with certain Honeywell units more often than expected. EASA says there is no evidence confirming a link to 5G and recommends Embraer's filter service bulletins; it is not an AD.

Australia

CASA set March 31, 2026 as the date after which aircraft without compliant radio altimeters may not fly ILS CAT II/III, SA CAT I/II or RNP-AR approaches at the listed airports.

What an anomaly looks like

The FAA describes two failure modes: no data, or wrong data. IFALPA calls wrong data the worse case, because it can be generated without the crew knowing. In AD 2023-10-02 the FAA listed the flight deck effects it was concerned about: erroneous TAWS warnings, erroneous TCAS warnings, erroneous landing gear warnings and erroneous radio altitude on the display. It warned that repeated false warnings raise workload and lead to "flightcrew desensitization to warnings," and that anomalies undetected close to the ground, for example in the flare, could cause loss of continued safe flight and landing.

Attribution is hard. The FAA received over 420 reports of anomalies near 5G deployments but said it lacks the means to tie any single event to 5G; CTIA asked for comparison data from before deployment, and none existed. IFALPA reminds pilots that bad radio altitude has caused accidents before, citing Turkish Airlines 1951 at Amsterdam in 2009 (not a 5G event), where, according to the Dutch Safety Board, the captain's radio altimeter suddenly read minus 8 feet and the autothrottle went to retard.

What depends on the RA

SAFO 21007 and the FAA's final rule list systems that may use radio altitude, depending on type:

TAWS/EGPWS, TCAS II and windshear detection
Autoland, CAT II/III, SA CAT I/II and EFVS operations
Automatic flight guidance, flight director, autothrottle, takeoff guidance and flight controls
Tail strike prevention, envelope protection, stick shaker and pusher
Thrust reversers, engine and wing anti-ice, and alert or warning inhibits
Altitude callouts and radio altitude on the PFD

What it means for pilots

For now, nothing changes in the U.S. Part 121 airplanes have had to be tolerant since February 1, 2024, and the wireless carriers' voluntary limits stay in place. Canada is a different story since July 1: if your fleet has any non-tolerant airplanes, check the AFM limitations before a low-visibility arrival in Canadian airspace.

The bigger change is a second retrofit, due by December 30, 2030. Aviation groups expect most of it to be done during overnight maintenance. After that date the FAA plans superseding ADs that bar non-compliant transport airplanes from low-visibility approaches and landings, and it says it does not plan to track individual airports for upper C-band interference.

Keep reporting anomalies. IFALPA and ALPA ask pilots to tell ATC right away and to file through ASAP or the company safety reporting system. Canada asks for a report to ATS and its Radio Altimeter Disturbance/Interference Report. Australia's CASA asks for reports of occurrences at or below 2,500 feet AGL, wrong radio altitude on takeoff or landing, and system faults caused by radio altimeter inputs.

Your company procedures and AFM come first. These rules set the deadlines; your fleet's service bulletins and ops specs will say what changes for your aircraft.

Sources

This is general information, not operating guidance. Your company's procedures, your aircraft's manuals and the regulations come first.