The risk of harmful interference with radar altimeters that operate in the band just above that frequency range could have been avoided if the wireless-industry trade group CTIA participated in a technical assessment performed by a multi-stakeholder group of the aviation technical advisory organization RTCA, wrote AOPA and 19 other groups in a May 12 letter to the FCC.
“As a result, any use of the conclusions by CTIA performed without the support of rigorous technical analysis are dangerous for the Commission to consider,” the aviation groups said, defending RTCA’s findings on C-band mobile telecommunications interference with radar altimeter operations.
The letter was filed in response to a March 2020 FCC order in which the FCC noted that “by licensing only up to 3.98 GHz as flexible-use spectrum, we are providing a 220-megahertz guard band between new services in the lower C-band and radio altimeters and Wireless Avionics Intra-Communications services operating in the 4.2-4.4 GHz band.”
The letter added that CTIA’s position “actually underscores both the need for the Commission to grant the pending Petition to Ensure Aviation Safety and the urgency for the Commission to work with the Federal Aviation Administration… to develop appropriate mitigations before 3700-3980 MHz operations commence in December 2021.”
AOPA reported in November 2020 on aviation’s concerns about the FCC’s movement to reallocate a portion of the 3.7 to 4.2 GHz frequency range for uses including “5G applications by the telecommunications industry.” In letters to the leadership of congressional committees with jurisdiction over transportation, aviation advocates pointed out that “radar altimeters are deployed on tens of thousands of civil aircraft in the United States and worldwide,” and are “the only sensor onboard a civil aircraft which provides a direct measurement of the clearance height of the aircraft over the terrain or other obstacles.”
In December, AOPA and aviation groups opened another front in the technological standoff, urging the FCC to suspend its auction of the 3.7 to 3.98 GHz spectrum—a position also backed by officials including House Committee on Transportation and Infrastructure Chairman Rep. Peter DeFazio (D-Ore.).
By contrast, CTIA praised then-FCC Chairman Ajit Pai for keeping the auction on schedule and for advancing fifth-generation wireless technology “even as we continue to identify and free up additional licensed mid-band spectrum for 5G services.”
In their letter to the FCC—now led by Acting Chairwoman Jessica Rosenworcel—the aviation groups countered what they see as hasty movement toward that goal, noting their commitment “to work with government and the commercial mobile wireless industry to achieve expeditiously a practical and achievable set of outcomes that both serves public and aviation safety and allows the American people to reap the benefits of new 3.7 GHz operations.”