Area Navigation and Flight Management: RNAV, FMS and Databases
RNAV concepts
Area navigation allows flight on any desired path rather than directly to or from ground stations. RNAV systems compute position from multiple sensors (VOR/DME, DME/DME, GNSS, inertial) and guide along defined waypoints and legs. PBN (performance-based navigation) specifies the required navigation performance (RNP) with on-board monitoring and alerting, versus RNAV which specifies only the navigation specification without the alerting requirement. RNP values (e.g. RNP 1, RNP 0.3) indicate the lateral accuracy in nautical miles to be maintained for 95% of the flight time.
FMS operation
The FMS combines a navigation database, flight plan, performance data and autopilot/flight director guidance. You must know: entering the active flight plan and departures/arrivals, checking the LEGS page for discontinuities, verifying waypoint coordinates against the chart, and understanding that the database is valid for a cycle (28 days) and must be current. Traps include assuming the FMS is always right, failing to cross-check the route, and confusing "pseudo-waypoints" (e.g. place/bearing/distance) with database waypoints.
Navigation database
The database contains waypoints, navaids, airways, airports and procedures; it does not contain terrain or weather. It must be updated each AIRAC cycle. If a waypoint is not in the database, it can be created as a pilot-defined point, but must be verified.
Worked example
A route requires RNP 0.3. This means the lateral navigation error must stay within 0.3 NM for 95% of the flight time, with on-board performance monitoring and alerting. If the aircraft's ANP (actual navigation performance) exceeds 0.3 NM, an alert is raised and the approach must not be continued.
Rule of thumb
"RNAV = specification; RNP = specification + on-board monitoring and alerting." Always cross-check the FMS route against the chart.