The FAA has issued two airworthiness directives (ADs) requiring flight manual revisions “to incorporate limitations prohibiting certain operations requiring radio [also called radar] altimeter data when in the presence of 5G C-Band interference.” The ADs stem from concerns that the planned rollout of wireless broadband operations in the 3.7-3.98 GHz frequency band (5G C-Band) could adversely impact radar altimeters, which operate in the 4.2-4.4 GHz frequency range. The ADs, one of which applies to transport and commuter category airplanes (PDF) and the other to helicopters (PDF), stipulate that the locations affected will be identified by future Notices to Air Missions (NOTAMs). The FAA also published a Special Airworthiness Information Bulletin (SAIB) concerning the potential effects of 5G deployment on radar altimeters last month (PDF).
This is a companion discussion topic for the original entry at https://www.avweb.com/flight-safety/faa-regs/faa-issues-5g-ads