Final answer:
The aircraft operator and flight crew are responsible for determining the most efficient navigation system for a flight operating under RNP, based on operational requirements, aircraft capabilities, and available air traffic services.
Step-by-step explanation:
When operating under Required Navigation Performance (RNP), the determination of which navigation system will be most efficient for a particular flight is typically the responsibility of the aircraft operator and the flight crew. They must take into consideration the operational requirements, aircraft capabilities, and the air traffic services available for the route. The navigation system chosen must meet the RNP specifications required for the flight's specific airspace or procedure. Modern aircraft often have flight management systems (FMS) that can work with a variety of navigation aids, and the most efficient system is often determined by factors such as the route, environmental conditions, and airspace restrictions.