The FAA effectively rejected assertions by the wireless industry and the Federal Communications Commission that 5G C-band transmitters can be activated in January as planned without putting aircraft at risk, pledging a cooperative approach to resolving safety concerns while setting the stage for weather delays and cancellations. The agency issued a pair of airworthiness directives (ADs) that take effect December 9 and are likely to limit a wide range of aircraft operations when the new 5G networks are activated, including scheduled passenger and cargo service, emergency response, and medical transportation.
The FAA issued two ADs December 7 that took effect December 9 (upon publication in the Federal Register), respectively applicable to transport category airplanes and all helicopters certified with radio altimeters installed. Also known as radar altimeters, these widely used devices provide pilots with the only direct measurement of distance above terrain, water, and obstacles.
The FAA expressed optimism that the issue can be resolved in a December 7 statement:
“The FAA believes the expansion of 5G and aviation will safely co-exist. Today, we took an important step toward that goal by issuing two airworthiness directives to provide a framework and to gather more information to avoid potential effects on aviation safety equipment. The FAA is working closely with the Federal Communications Commission and wireless companies, and has made progress toward safely implementing the 5G expansion. We are confident with ongoing collaboration we will reach this shared goal.”
The issue has been brewing for years, including throughout the FCC process that culminated in 2020 with the authorization to activate new 5G wireless transmitters operating on the C-band. Transmitters were originally scheduled to go online early this month in 46 of the most populated areas of the country. A broad-based coalition of aviation advocates (including AOPA) urged delay of that activation, given documented evidence that the C-band cellular traffic could interfere with radio altimeters operating on nearby frequencies. AOPA, the National Business Aviation Association, Helicopter Association International, and other general aviation organizations, as well as companies and groups representing the air transport sector, issued a statement December 8 in response to the new ADs that first thanked the FAA for acting to protect safety, and then warned that significant air travel disruption is likely absent mitigations beyond what the wireless industry recently proposed, such as limiting the power output of certain transmitters.
“While appreciated, the mitigations proposed by AT&T and Verizon are inadequate and far too narrow to ensure the safety and economic vitality of the aviation industry and the millions of people traveling by air each year,” the aerospace coalition wrote in the joint statement, noting that the group has also proposed an alternative for the FCC to consider, “which builds on the voluntary telecom proposal and provides additional safeguards in, around, and on the approach to airports and heliports. The proposal aims to minimize the impact on both the telecom operations and our national aviation system.”
While the wireless industry has long argued that 5G C-band does not risk interference with radio altimeters, the FAA, in the ADs, cited findings to the contrary by an RTCA 5G Task Force that conducted a risk assessment and issued a report in 2020, including the results of interference tests with several common radar altimeter models. The FAA noted in the related ADs that the task force report concluded that there remains “‘a major risk that 5G telecommunications systems in the 3.7-3.98 GHz band will cause harmful interference to radar altimeters on all types of civil aircraft—including commercial transport airplanes; business, regional, and general aviation airplanes; and both transport and general aviation helicopters.’”
The FAA further noted that its own assessment affirmed the RTCA findings:
“The FAA risk assessment included consideration of the RTCA report, public comments to the RTCA report, and analyses from radio altimeter manufacturers and aircraft manufacturers in support of the safety risk determination. The analyses FAA considered were consistent with RTCA’s conclusions pertaining to radio altimeter interference from C-Band emissions. The FAA determined that, at this time, no information has been presented that shows radio altimeters are not susceptible to interference caused by C-Band emissions permitted in the United States,” the agency stated in the ADs.
The FAA also addressed the wireless industry's claim that 5G C-band networks have not caused such interference in other countries: “In some countries, temporary technical, regulatory, and operational mitigations on C-Band systems have been implemented while aviation authorities complete their safety assessments. Under the FCC rules adopted in 2020, base stations in rural areas of the United States are permitted to emit at higher levels in comparison to other countries which may affect radio altimeter equipment accuracy and reliability.”
The Aerospace Industries Association (AIA) leads the coalition of aviation stakeholders formed to address the issue, and the coalition noted that its own risk mitigation proposal, submitted December 6, seeks to preserve safety while enabling the next generation of wireless connectivity without unnecessary delay:
“With the current launch date of January 5, and the ADs just being released, it is clear we need to get this balance right," the aerospace coalition said December 8. "We strongly urge for a further delay in 5G deployment for the data sharing and consultations necessary to create a win-win situation for both industries.”
The FCC expressed optimism that the issue can be resolved in a December 7 statement reported by Bloomberg:
“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. We look forward to updated guidance from the FAA in the coming weeks that reflects these developments.”
The proposal from the AIA-led aerospace coalition expands on the mitigations proposed by the wireless industry that the FCC referred to.
Meanwhile, with C-band base stations still on track to activate in January, the two ADs instruct operators to modify aircraft flight manuals at an estimated cost of $85 per aircraft, or $580,890 across the fleet of fixed-wing aircraft, and $155,380 for the rotorcraft fleet currently in service.
Notams will follow for specific locations as 5G C-band transmitters are activated advising operators when radar altimeters can no longer be trusted for use in various procedures, including off-airport landings in bad weather by emergency medical services helicopters.
“Potential impacts include: delayed and cancelled passenger flights; delayed air cargo shipments; significant schedule disruptions; and inability for first responders, military, and law enforcement to fly helicopter missions. We will have a full assessment of the impact of the ADs in the coming days,” the aviation coalition noted.
Members of the aviation coalition also worked to educate aviators, regulators, and the public about the details of an issue that has for several years prompted repeated warnings and pleas for appropriate mitigation. NBAA hosted an hourlong discussion on the topic online December 7, and AOPA has also worked, as a member of the aviation coalition, to encourage cooperative risk mitigation.