Industry Balks At The FAA’s 5G Risk-Mitigation Plan

regional jet on an airport apron
Regional jets are particularly vulnerable to interference from 5G C-band signals, leaving some concerned they may not have access to certain airports as new wireless services roll out.
Credit: Sean Broderick/AW&ST

A handshake agreement between the FAA and telecommunications companies to phase in new 5G C-band wireless networks near airports over the next year has many aviation industry stakeholders concerned that they will not be able to meet the agency’s targets.

The agreement, announced by the FAA in mid-June, “will continue to enable aviation and 5G C-band wireless to safely coexist” as wireless companies steadily expand their services through July 2023, FAA Acting Administrator Billy Nolen said. It calls for operators to modify their aircraft to protect radio altimeters, or radalts, based on a schedule that factors in wireless companies’ plans to expand services around airports.

The initial services have been rolled out by AT&T and Verizon Wireless, the two biggest winners in the 2021 Federal Communications Commission (FCC) auction that doled out the so-called “midband” wireless spectrum at 3.7-3.98 GHz. But 19 other companies won licenses, too, and many plan to launch services over the next year. Their plans, plus AT&T and Verizon’s desire to maximize their networks, mean that aviation cannot continue to count on wireless stakeholders’ voluntary mitigation strategies put in place since the first towers were activated in January.

Instead, aircraft—specifically the radalts that have long used the 4.2-4.4 GHz spectrum—must be protected from the risk of signal interference. Aircraft that are not modified must avoid airspace near the new towers during certain flight conditions, such as when flying instrument approaches. Some may not be allowed to fly near 5G towers at all.

A radalt calculates an aircraft’s absolute altitude—or height above whatever is below—by measuring how long it takes electromagnetic waves to travel from the aircraft to the surface below and back. Used at lower altitudes, they are crucial for low-visibility operations. Their data supports key automated functions on many aircraft, including traffic-alert and collision-avoidance systems, enhanced ground proximity warning systems, automatic braking, terrain awareness warning systems and stick-shaker stall warnings.

Interference from signals in nearby spectrums can cause radalts—which must meet technical standards defined more than 40 years ago, before the first commercial cellphone existed—to malfunction. If incorrect altitude data is fed to the aircraft or the calculation is delayed, problems can arise quickly. Since pilots must rely on their instruments and aircraft systems, the risk of inaccurate data is not acceptable—hence the need to modify or replace radalts if the 5G networks are rolled out.

The FAA’s plan divides the estimated 7,500 affected domestic and international aircraft into three groups. Group 1 aircraft, the most affected by current and planned network rollouts, comprises Embraer’s regional jets. The FAA’s plan targets this November for upgrades to the fleet, according to an agency presentation shared among stakeholders in late July and seen by Aviation Week.

Group 2 comprises the Airbus narrowbodies, with a retrofit target deadline of January 2023.

Group 3 is broken into three subgroups and has the most models, including the Boeing 737 Next Generation, MAX and 777 fleets; MHI/Bombardier regional jets; and Airbus A380s. Some face a March 2023 deadline, while the rest have until July 1, 2023.

“Filters and replacement units for the mainline commercial fleet should be available on a schedule that would permit the work to be largely completed by July 2023,” the FAA said in announcing the agreement.

Many in the industry are not convinced. The U.S. Regional Airline Association (RAA) pushed back immediately on the FAA’s tentative plan, citing the potential vulnerability of many regional aircraft its members fly as the 5G services are expanded near smaller airports.

“Commercial airline altimeters are not broken; they are working exactly as they were designed and certified to work. The new signal interference is the change,” the RAA said. “Nonetheless, airlines have begun making costly retrofits to overcome the new interference. However, after this current extensive round of modifications, it is not clear if these modifications will even allow access to all airports in [instrument] conditions once additional telecom providers enter the market later this year.”

A July 18 letter to Nolen from the International Air Transport Association (IATA) and signed by eight airline associations representing most major non-U.S. carriers raised similar concerns. Among them: Radalt suppliers have said supply chain issues mean the deadlines will be tough to meet even without factoring in time for the FAA to validate the filters or aircraft manufacturers to develop service bulletins.

“Following the availability of the service bulletins, the minimum lead time for various . . . retrofit solutions is estimated at 6-9 months, leaving little time for installation on impacted aircraft before the July deadline,” the letter said.

The FAA’s stakeholder presentation says retrofits have already started for some regional jets, and “other manufacturers are making progress.”

The current plan “is doable,” a government source tells Aviation Week. “But it requires the aviation industry to make it an urgent priority.”

The FAA concedes that suppliers and maintenance providers are concerned about meeting the target upgrade deadlines.

“Manufacturers have raised general concerns about potential supply chain and maintenance capacity issues,” the presentation said.

Non-U.S. carriers worry that their American counterparts may be prioritized since more of their fleets need the upgrades compared to airlines that send only some of their aircraft into the affected airspace.

“The radalt manufacturers reported that supply chain issues will make it extremely difficult for them to deliver enough retrofit kits to enable airlines to meet the July 2023 deadline,” IATA said. “This will be particularly true for foreign carriers, given the clear focus on meeting the needs of the U.S. domestic market.”

The FAA’s plan assumes some aircraft will not be retrofitted by the deadlines, meaning airlines will either have to dispatch aircraft based on their capabilities or cancel flights.

“Foreign carriers will find it extremely challenging to restrict their aircraft fleet, possibly down to specific tail numbers that can service U.S. destinations,” the letter said. “All carriers require a degree of aircraft fleet interoperability to ensure that their schedules are reliable, and the specific aircraft type chosen can operate globally.”

In the interim, IATA urged U.S. regulators to learn from examples set by other countries. Canada has ordered mitigations developed for a different part of the spectrum to be adopted in the 3650-3900 MHz spectrum slated for auctioning in 2023.

“Commercial airline operators noted that in the absence of the proposed extension of the current 3500 MHz band mitigations into the 3800 MHz band, airlines will be forced into limitations on operations that have the potential to add significant risk to the safety of their flight operations compared to those enjoyed today and would impose burdensome costs,” explains a Canadian government policy document published last month.

Brazil’s national telecommunications agency issued a policy in June with specific standards for 5G deployments near airports. They include establishing exclusion zones around runways and specifying how cellular antennas must be oriented to minimize potential interference in nearby airspace.

“We urge the FAA to work with all relevant parties” in both aviation and the wireless industry, IATA said, “to achieve a solution that more fairly and realistically allocates the responsibility to ensure that 5G and aviation can safety coexist both in the short and long term.”

Sean Broderick

Senior Air Transport & Safety Editor Sean Broderick covers aviation safety, MRO, and the airline business from Aviation Week Network's Washington, D.C. office.