Technically, very easy. But (IIRC) those other systems are not "officially recognized" by either the FCC (frequency protection) or the FAA. So an airplane oper

Technically, very easy. But (IIRC) those other systems are not "officially recognized" by either the FCC (frequency protection) or the FAA. So an airplane operator cannot use them for navigational purposes without opening themselves up to litigation because they're not following FAA directives. FCC recognition of Galileo is limited in scope: * https://www.gpsworld.com/fcc-approves-use-of-galileo-for-non-federal-official-use/ https://www.gpsworld.com/fcc-approves-use-of-galileo-for-non...