The aviation news site AVweb's report on a "Special Airworthiness Information Bulletin" and "Airworthiness Directive" being issued by "

The actions will limit the use of automated systems on aircraft that rely on radar altimeters (also called radio altimeters) and flight delays and cancellations may result. Reuters found a letter from FAA Deputy Administrator Bradley Mims that says the agency shares "the deep concern about the potential impact to aviation safety resulting from interference to radar altimeter performance from 5G network operations in the C band."

Radar altimeters operate in the 4.2-4.4 GHz frequency range (their sweet spot), and the fear is that the nearby powerful mobile signals will cause interference for the avionics. However, the FCC approved the use of the spectrum for 5G saying "well-designed [radio altimeter] equipment should not ordinarily receive any significant interference (let alone harmful interference)."

Aviation groups say the risk for thousands of aircraft is real, and the FAA seems to agree.