Story ID: 
FCC’s Upper C-band Proposal Seeks Aviation Input
By: Gordon Gilbert
Caption: FCC directed to auction off spectrum in upper C-band
Word Count: 319
The U.S. Federal Communications Commission (FCC) has posted a draft notice of proposed rulemaking (NPRM) on its previously disclosed plan to auction up to 180 MHz of spectrum in the 3.98 to 4.2 GHz (the upper C-band) for next-gen wireless services. Unlike past rulemaking on lower C-band expansion that caused interference with radio altimeters, comments on this NPRM are expressively being sought from the aviation community.
Radio altimeters operate in the adjacent 4.2- to 4.4-GHz band. The FCC acknowledged its failure in previous frequency band expansions to address adjacent band inequities. Consequently, we “will necessitate broad-based and proactive engagement from relevant industry stakeholders, as well as our federal partners,” including the FAA.
The FCC intends to apply the same framework used in the 2020 lower C-band auction—3.7 to 3.98 GHz—which allocated 280 MHz for flexible wireless use and expanded 5G access. However, it also caused flight disruptions due to radio altimeter interference, and to resolve the issues, avionics manufacturers were forced to hurry the development of radio altimeter retrofits, followed by FAA airworthiness directives in 2023.
“There are also ongoing aviation industry-led efforts to design next generation radio altimeters that predate the instant FCC proceeding but nonetheless may lead to the production and deployment of more resilient [radio] altimeters in the near future,” according to the FCC. “To that end, we expect the FAA to initiate and complete a rulemaking to codify the new radio altimeter standards in parallel with our rulemaking and prior to any auction.” Congress has mandated that the auction be complete by July 4, 2027.
Regardless of the assurances made in the NPRM of “close coordination” by the FCC with the FAA, and asking for comments specifically from stakeholders, aircraft operators are girding for possible frequency interference issues based on their experience during former band expansions. Comments will be accepted for up to 30 days after the date the final NPRM is published.