The FAA’s analysis of 5G cellphone network C-band transmitter effects on aircraft radio altimeters has shown that the impact on aviation operations is in specific areas. At the same time, the agency has determined how the C-band signals affect aircraft radio altimeters and how these avionics units can be upgraded to tolerate the interference. In light of this new information, the FAA is proposing to revise AD 2021-23-12 to reflect new operational requirements.
In discussing the impact of 5G networks, the FAA said it received more than “420 reports of radio altimeter anomalies within a known location of a 5G C-band deployment.” However, the agency added, “Approximately 315 of these reports were determined to not be related to 5G C-band interference and were resolved through normal continued operational safety procedures.”
About 100 reports within the areas covered by FAA 5G notams could not be ruled out, according to the FAA. “These…incidents included various flight deck effects such as erroneous terrain awareness and warning system warnings, erroneous traffic collision avoidance system warnings, erroneous landing gear warnings, and the erroneous display of radio altimeter data.”
Because 5G networks are expanding and the frequencies they use are close to those of radio altimeters, the revised AD will add "interference tolerance requirements for radio altimeters that can be used across the affected fleet.” Non-radio altimeter-tolerant aircraft will continue to face operational restrictions and retrofits would have to be done by Feb. 1, 2024.