Planned 5G rollout risks aviation safety

It was not immediately clear how many of the new 5G ground station transmitters that have raised concern among aviation safety experts would be affected by the voluntary one-month delay announced by AT&T and Verizon. New 5G C-band base stations located in 46 of the most populated areas in the United States all appear to have significant potential to interfere with aircraft navigation, rendering inaccurate or nonfunctional radar altimeters installed on thousands of aircraft to guide passenger airliners and cargo deliveries in poor weather, as well as business jets, emergency medical transport helicopters, and other aircraft.

"While this news is a positive step, we ask you to continue to work to ensure that the additional time results in the goal we've had all along, which is to continue safe and efficient aviation operations in the United States National Airspace System (NAS) without disruption from 5G flexible use operations in the C-Band," the coalition wrote November 5 in a letter signed by AOPA and 20 other organizations and aerospace companies. The coalition urged the administration "to convene a joint industry working group and continue to delay the deployment of 5G technologies in this band until the safety and efficiency of the NAS is ensured. The goal of this working group would be to reach acceptable mitigations."

The wireless industry has for years expressed skepticism that 5G transmissions could affect radar altimeters (also known as radio altimeters), despite evidence presented to the public and the FCC that such interference appears to be inevitable absent changes to base station configuration. Wireless carriers appeared to acknowledge this possibility for the first time on November 4:

"At the request of the Department of Transportation, today we have voluntarily agreed to defer Phase I C-Band deployments for one month to January 5 while we continue to work in good faith with the FCC and the FAA to understand the FAA’s asserted co-existence concerns," AT&T said in a statement provided to AOPA. "It is critical that these discussions be informed by the science and the data. That is the only path to enabling experts and engineers to assess whether any legitimate co-existence issues exist."

Verizon spokesman Rich Young confirmed in an email exchange that activation of its C-Band service will be postponed similarly, "for 30 days (from December 5, 2021 to January 4, 2022). We're doing this as a good faith gesture to try and continue to work with the FAA on issues it claims to have on radio altimeters."

AOPA Senior Vice President of Government Affairs Jim Coon said AOPA very much appreciates the FAA and DOT's efforts and concurs with holding off on this 5G rollout given that experts believe radar altimeter interference is a real threat. He also said that he believes that more than a month will be needed to determine what specific mitigations should be put in place to adequately address aviation safety concerns.

AT&T and Verizon announced the delay activating their 5G transmitters days after the FAA began taking action to mitigate this risk, starting with an advisory to pilots and aircraft operators that sets the stage for imposition of aircraft operational limitations that would be all but certain to disrupt air travel systemwide, and for long periods of time. The FAA has limited options to ensure safety if the Federal Communications Commission does not require adjustments to 5G wireless transmitters as presently authorized.

Potential interference with critical navigation equipment caused by powerful new C-band 5G wireless transmitters (currently cleared by the FCC to activate on December 5) could force airlines, along with many flights by helicopters, business jets, and cargo operators, to suspend operations in poor weather. Pilots, aircraft manufacturers, and safety advocates have for the past five years asked the FCC to consider such adverse impacts on aviation—specifically, interference with the only sensor on an aircraft that directly measures distance to the ground below—when allocating adjacent bandwidth for fifth-generation wireless devices.

A coalition of aviation advocates in November 2020 asked congressional leaders to step in, re-stating concerns previously raised during the FCC process that culminated in reallocation of portions of the 3.7 to 4.2 GHz frequency band, followed this year by auctioning the 3.7 to 3.98 GHz frequency range to 5G wireless providers.

Tests of 5G base station equipment operating near various radar altimeters currently in widespread use were conducted by RTCA, a nonprofit association that develops consensus policies for aviation modernization, with the measurements and analysis documented in a white paper published in October 2020. RTCA found that radar altimeters, which all transmit on frequencies between 4.2 GHz and 4.4 GHz, are susceptible to both inaccuracy and outright failure when operated near 5G base stations, many of which are located close to major airports, and which have been cleared by the FCC to begin transmitting on December 5.

RTCA determined that there is "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 results of the study performed clearly indicate that this risk is widespread and has the potential for broad impacts to aviation operations in the United States, including the possibility of catastrophic failures leading to multiple fatalities, in the absence of appropriate mitigations."

Neither the FCC nor wireless operators have taken any action that would mitigate this risk, such as mandating (or voluntarily adopting) lower power settings on 5G transmitters near airports, or adjusting the transmitter antenna orientation to limit potential interference. (RTCA noted in its report that while radar altimeters differ somewhat in design and function, they all transmit at low power, and require very sensitive antennae to capture the return signal bouncing back, separate it from noise, and calculate the distance.)

The FAA issued on November 2 a special airworthiness information bulletin advising aircraft operators and pilots about the pending 5G activation, and noted that the FAA "is currently collaborating" with the FCC and the National Telecommunications and Information Administration "to assess the need for mitigation beyond the recommended action in this SAIB."

The coalition of aviation organizations and industry leaders, formed to support a commonsense solution to this critical safety problem, met November 3 with representatives of the DOT and the National Economic Council, an organization within the White House that advises the president on U.S. and global economic policy. AOPA continues to coordinate with Helicopter Association International and the National Business Aviation Association to represent GA interests in these ongoing discussions, working with fellow coalition members including the Air Line Pilots Association, Airlines for America, and avionics manufacturers to advocate for mitigations adopted by countries such as France and Canada, where 5G transmitters near airports are operated within certain constraints.

"We are thankful the White House and FAA share our concern about the potential impacts on aviation safety," said Coon. "We all want fast wireless, and we fully support responsible upgrades of this infrastructure. But the critical issue here is the safety of everyone who uses the national airspace system. Interfering with a safety device that has proved its value for decades is just not worth the risk."

One or more radar altimeters are installed on thousands of military and civilian aircraft around the world, and many legacy models (the technology is 40 years old) remain in service, which casts doubt on the feasibility of modifying in-service devices, particularly in the time available before the new 5G transmitters are authorized to begin operation December 5. Radar altimeters are used in all phases of flight for various kinds of operation, including approach and landing (not always at airports, in the case of medical helicopters) to maintain pilot awareness of terrain and obstacles, particularly (though not exclusively) in reduced visibility.

The FAA has few options available to protect the flying public if the 5G system begins operating as presently authorized. Wishful thinking does not safeguard low-altitude operations in limited visibility, and the FAA has historically taken a conservative approach to safety, making it unlikely the agency will simply wait and see what happens. In light of what RTCA documented, along with the many remaining unknowns such as the effect of 5G devices used aboard aircraft by passengers who don't know or don't care that they may be causing a hazard, it is hard to imagine that the FAA will not take action to disallow operations and procedures that utilize radar altimeters absent the mitigations that aviation advocates have long sought from the FCC.

That is the other reason why the White House has taken a strong interest: The economic damage caused by flight cancellations that impede passenger travel and further disrupt an already-compromised supply chain during the height of the holiday season would likely be significant. Such disruptions could also spill over into the rest of aviation if increased workload limits availability of air traffic control services provided to all airspace users.