New AD Demands 5G-Tolerant Radio Altimeters for Part 121 Operations Near Cell Towers

Carriers will need to equip their aircraft with 5G C-Band tolerant altimeters by February 2024 according to Airworthiness Directive AD-2022-01379.

The newly issued AD supersedes 2021-23-12, which applies to all transport and commuter category aircraft equipped with a radio altimeter. The older AD requires revision of the limitation section of the aircraft's POH to incorporate limitations from operations from using radio altimeter data in the presence of 5G C-Band interference identified by NOTAM. 

Since then, the FAA has "determined that additional limitations are needed due to the continued deployment of new 5G C-Band base stations whose signals are expected to cover most of the contiguous United States at transmission frequencies between 3.7-3.98 GHz. This proposed AD would require revising the limitations section of the existing airplane/aircraft flight manual to incorporate limitations prohibiting certain operations requiring radio altimeter data, due to the presence of 5G C-Band interference. This proposed AD would also require modifying certain airplanes to allow safe operations in the United States 5G C-Band radio frequency environment."

Also in the AD is a requirement that would prohibit radar-altimetry-dependent landings in low visibility after June 30, 2023. That places it around the same time as the end of the voluntary C-Band limitation imposed by cell carriers in 2021, when they can once again broadcast at full strength. For now, at least, carriers still have some time to procure and install compliant equipment, though the supply chain for suitable altimeters may still take some time to catch up after recent difficulties. 

FMI: www.federalregister.gov