Definition
An area navigation (RNAV) system that meets the FAA's required performance and integrity standards for the phase of flight in which it is being used, and is therefore approved as a substitute means of navigation in place of conventional ground-based navigation aids such as VORs, DMEs, NDBs, and compass locators. To qualify, the system must be properly installed, operational, and used within the limitations specified in the aircraft's Aircraft Flight Manual, Pilot's Operating Handbook, or other FAA-approved documentation.
Plain English
An on-board GPS or other area navigation system that the FAA accepts as good enough to fly a route or procedure without needing the old-style ground stations.
Context Anchor
Seen during flight planning, when accepting RNAV clearances, and before using an RNAV route, departure, arrival, or approach.
Derivation
Suitable' here doesn't mean 'good enough in the pilot's opinion.' It's a regulatory term meaning 'meets the specific FAA criteria for this use.' RNAV stands for Area Navigation -- a method that lets an aircraft fly any desired path, not just along the line between two ground stations.
Why Pilots Care
Using a system that does not qualify can result in navigation errors, loss of ATC clearance, or unsafe flight.
Intuition Check
Do not assume “suitable” means “the navigation display seems to work.” Here it means approved, capable, and appropriate for the specific RNAV operation.
Example Sentence 1
Because the aircraft was equipped with a suitable RNAV system, the pilot was able to identify the intersection without tuning the VOR.
Example Sentence 2
Only aircraft equipped with a suitable RNAV system may fly the published RNAV approach to the airport.