FAA Proposing C-Band-Based Rules That Could Limit Some Flights

Radio altimeters "cannot be relied upon" in the presence of interference from wireless broadband in the 3.7-3.98 GHz band, the FAA said in airworthiness directives Tuesday for transport and commuter planes and helicopters using radio altimeters. It said it's proposing flight manual limits that would bar some operations requiring radio altimeter data around airports that will have C-band base stations or other devices that could affect airplane systems. Those operations include some instrument approach procedures and use of enhanced flight vision systems for landing. The proposed rules repeatedly cite the RTCA study on interference risks (see 2010280048). Such limits could prevent flights, particularly to locations with low visibility, "and could also result in flight diversions," the FAA said.

Other FAA proposals may be forthcoming. The agency said the most immediate risk is using radio altimeters to land in low visibility, but other automated safety systems rely on radio altimeter data and it's collecting data on possible effects to those systems "to determine whether additional mitigations are necessary."

The FCC "continues to make progress working with the FAA and private entities to advance the safe and swift deployment of 5G networks, as evidenced by the technical mitigations wireless carriers adopted last month," a commission spokesperson emailed. "We look forward to updated guidance from the FAA in the coming weeks that reflects these developments."

The FAA lacks technical expertise to understand 5G signal propagation and how much exposure the altimeters will get from it, and is overreacting, said High Tech Forum founder Richard Bennett. "This is one of those 'out of an abundance of caution' things," he said, saying the agency is particularly adverse to risk after controversy about its regulatory oversight after 2018 and 2019 fatal crashes involving systems on the Boeing 737 MAX. He said once NTIA administrator nominee Alan Davidson is confirmed, an agreement between the FAA and FCC could come within six months. Bennett said the rollout of 5G C band could be slower around general aviation airports except for a few that are a test bed for seeing what problems arise and possible technical fixes. A lawyer with satellite clients said, with the C-band clearing still in Phase I, there's time for an engineering solution to be developed.

"Air safety is of paramount importance, but there is no evidence that 5G operations using C-band spectrum pose any risk to aviation safety, as the real-world experience in dozens of countries already using this spectrum for 5G confirms," Verizon said. "While the new directives suggest the FAA plans to further analyze this issue, we are confident that it will conclude -- as the FCC already found -- that 5G over C Band poses no risk to air safety. Today's FAA directives also do not take into account the precautionary measures that Verizon and AT&T recently agreed to that will provide additional protections around airports and helipads as the FAA completes its analysis. We are on track to launch 5G using C-band next month and to reach 100 million Americans with this network in" Q1.

The temporary voluntary power limits and antenna restrictions on C-band deployments near airports (see 2111240062) it and Verizon are undertaking weren't taken into consideration in the FAA directives, AT&T said. "We recognize the paramount importance of air safety, and our use of the C-band spectrum will not undermine that imperative," AT&T said. "Our networks will comply with the regulations carefully crafted by the FCC, the government’s expert agency on spectrum use, to allow C-band 5G service to safely co-exist with aviation.”

Well-founded safety concerns need to be raised, but the FAA's process and timing for 5G has "been less than ideal," and there needs to be more proactive engagement from and cooperation among federal agencies so concerns get addressed and operations can move forward, blogged Jeffrey Westling, American Action Forum technology and innovation policy director. He said the FCC/FAA disagreements over the C band, and FCC clashes with NASA and NOAA over the 24 GHz band, show the need for more streamlined collaboration between the FCC and the executive branch, using common understanding of technical parameters. He said more technical capacity at and an updated memorandum of understanding between the agencies could be helpful. "As long as the coordination process between executive branch agencies and the FCC continues to falter, these disputes will continue to arise," he said.

The aviation industry is suggesting technical modifications Verizon/AT&T C-band rollout precautions. The Aerospace Industries Association in FCC docket 18-122 said the wireless carriers' plan is "inadequate and far too narrow to ensure the safety and economic vitality of the aviation industry." It said its power flux density limits counterproposal "builds on the telecom proposal" with more safeguards in and around airports and heliports. Asked about the AIA proposal, Verizon and AT&T didn't comment. The Aerospace Vehicle Systems Institute released in three filings data used for the RTCA study. "It is hoped that this release will be reciprocated in kind by the 5G community, as multiple requests for 5G power and other parameters are still outstanding in the Commission’s public record," AVSI said.