You probably heard the buzz about 5G wireless broadband cell towers interfering with aircraft radar altimeter systems (also called radio altimeters). And now there are two FAA Airworthiness Directives (AD 2021-23-12 and 2021-23-13) in place. The latter is focused on helicopter operations. In part, the ADs say that radio altimeters are unreliable if they experience interference from wireless broadband operations in the 3.7-3.98 GHz (5G C-band) frequency spectrum.
Aside from lots of people wondering why aircraft navigation systems weren’t considered during the 5G broadband design process, the AD has created a lot of confusion, especially among pilots who fly with radar altimeters in some lower-end GA aircraft.