This time it’s not the continuing controversy over whether the proposed 5G Ligado Networks wireless communications system operating in the L-band will jam GPS reception that is galvanizing aviation to action.
According to a recently released technical report, a move by the Federal Communications Commission to allocate some C-band spectrum for 5G could compromise the operation of radar altimeters—the only sensors aboard civil aircraft that provide “a direct measurement of the clearance height of the aircraft over the terrain or other obstacles”—on adjacent frequencies.
In a November 17 letter to the bipartisan leadership of House and Senate committees with jurisdiction over transportation, AOPA and 13 other aviation organizations raised concerns about the FCC’s action to reallocate a portion of the 3.7- to 4.2-GHz frequency range for uses including “5G applications by the telecommunications industry.”
“The aviation industry noted in the FCC rulemaking process that deployment of 5G networks in this frequency band may introduce harmful radio frequency (RF) interference to radar altimeters currently operating in the globally-allocated 4.2–4.4 GHz aeronautical band,” the letter said.
“Radar altimeters are deployed on tens of thousands of civil aircraft in the United States and worldwide to support several critical safety-of-life aircraft functions throughout multiple phases of flight. Radar altimeters 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,” it said.
Buttressing the groups’ request for lawmakers to agree to “direct involvement with key stakeholders to protect the frequency bands used by radar altimeters” was a task force report from the technical organization RTCA that “revealed a major risk” of harmful interference with radar altimeters from 5G telecommunications systems in the 3.7- to 3.98-GHz bandwidth.
Adverse impacts include “the possibility of catastrophic failures leading to multiple fatalities, in the absence of appropriate mitigations,” they wrote.
On February 28, the FCC announced action “to free up C-band spectrum for 5G services,” making “a wide swath of mid-band spectrum available for 5G through a public auction.”
The action would make the spectrum “available quickly, while generating substantial revenue for the United States Treasury. At the same time, the item ensures the continuous and uninterrupted delivery of video programming services and other content to the American people that is currently delivered by satellites using the C-band,” said the FCC’s news release.
RTCA, a nonprofit association that develops consensus policies for aviation modernization, released a white paper on the interference issue in October, directing its findings to the FCC.
“A thorough understanding of the risks associated with this interference and the impact on aviation safety will be vital in bringing both aviation and spectrum regulators together to ensure that safety-critical aviation systems will continue to be protected for the purposes of public safety,” RTCA President and CEO Terry McVenes said in a news release.
The new challenge to the FCC’s spectrum allocation for 5G comes at a time when aviation organizations and numerous other industries that depend on GPS have been urging the regulatory agency to reconsider its approval in April of the Ligado Networks plan for a wireless communications network that would transmit in the L-band.
Ligado’s critics remain concerned that the network’s radiation could jam or overwhelm reception of low-powered GPS signals sent from satellites on adjacent frequencies. Ligado has responded that it has addressed the concerns as a condition of its FCC approval and recently reported on steps it is taking to stand up its network.