The FAA proposes to supersede Airworthiness Directive (AD) 2021–23–13, which applies to all helicopters equipped with a radio altimeter, by prohibiting certain operations when in the presence of possible 5G C-band radio frequency interference in areas identified by notams.
Since the issuance of AD 2021–23–13 in December 2021, the FAA has determined that additional limitations are needed. Whereas 5G C-band transmissions were initially limited to 3.7 to 3.8 GHz, these transmissions have also begun to expand to 3.8 to 3.98 GHz, and the FAA expects deployment at the higher end of the frequency range to expand after July 1.
“These higher frequencies are nearer to the spectrum allocation where radio altimeters operate (4.2 to 4.4 GHz), which means that the potential for interference to radio altimeters from in-band and spurious emissions may be more likely,” said the agency. “In addition, the FAA expects approximately 19 additional telecommunication companies in addition to AT&T and Verizon will begin transmitting in the C-band at some point after June 2023.”
This proposed AD would require revising the limitations section of existing rotorcraft flight manuals to prohibit certain operations requiring radio altimeter data due to the presence of 5G C-band interference. The agency estimates that this new AD would affect 1,128 helicopters of U.S. registry. Comments on this proposed AD are due by May 12.