Final answer:
The aviation regulatory authority of a country, like the FAA in the United States, determines if GPS RNAV can be used as the primary means of navigation, taking into account performance, compliance, and international standards.
Step-by-step explanation:
The determination of whether GPS RNAV (Area Navigation) can be used as the primary means of navigation on aircraft is made by the aviation regulatory authority of a specific country. In the United States, for instance, this responsibility lies with the Federal Aviation Administration (FAA). The FAA sets out the regulations and requirements for the different types of navigation aids that can be used for various phases of flight. Deciding on the primary means of navigation involves considerations about the performance of the navigation system, regulatory compliance, operational procedures, and the availability of the satellite signal. The International Civil Aviation Organization (ICAO) also provides standards and recommended practices for international flights, which must be considered alongside the regulations of the specific country.