The protracted row between the Federal Communications Commission (FCC) and the FAA over the rollout of AT&T and Verizon 5G C-band service hit the pause button earlier this month, with the wireless carriers offering accommodations that at this writing appear to mollify the concerns of commercial air carriers at the U.S.'s largest airports. At issue, the impact of wireless signals in the 3.7 to 3.98 GHz range bumping up against radar/radio altimeters that live in the 4.2 to 4.4 GHz environment, causing those altimeters to give potentially false readings to pilots and the various aircraft systems they support, endangering aviation safety, particularly during takeoff and landing in low visibility conditions. The apparent solution on the horizon is to adopt a version of accommodations already in place at France’s largest airports and in Canada—powering down C-band base stations near runways and aiming wireless tower antennas downward at steeper angles. 

Some variant of this solution was suggested by the wireless carriers, the airlines’ trade association, Airlines For America (A4A), and the Airline Pilots Association International (ALPA). But while this détente addresses the concerns of the major airlines, it does little to assuage the concerns of regional carriers, business and general aviation, and particularly the rotorcraft community. There are also national security implications as a good chunk of the U.S. military’s aircraft rely on older technology unmodulated pulse style radar altimeters more susceptible to C-band interference, as opposed to more modern frequency-modulated continuous-wave (FMCW) technology in newer models. But even those have some susceptibility. Existing radar altimeters cannot be economically modified to defeat this interference and new models that do are just now coming to market. If the recent ADS-B mandate is any indication, it could be a decade or more before a meaningful fleet retrofit is achieved and then, of course, there is the thorny issue of who should pay for it.