Definition
The function of VOR/DME RNAV (Area Navigation) is to allow a pilot to fly direct to any point within reception range of a VOR/DME station, without being restricted to flying directly to or from the station itself. The system electronically shifts, or 'offsets,' the VOR/DME signals to create a phantom station, called a waypoint, at any chosen latitude/longitude, bearing, and distance from the actual ground station. The aircraft then navigates to that waypoint as if it were a real VOR/DME, using inputs of bearing and distance from the underlying station combined with onboard computation to display course guidance and distance-to-waypoint information.
Plain English
VOR/DME RNAV lets you fly straight to a point in space that isn't a real navigation station. The equipment uses a real VOR/DME on the ground, then mathematically creates an imaginary station wherever you want it, so you can fly direct to that point instead of being forced to fly over the actual ground station.
Context Anchor
Seen in instrument navigation discussions, especially with older area navigation equipment that uses ground-based VOR and DME signals rather than GPS.
Derivation
RNAV stands for 'area navigation,' meaning navigation across an area rather than along fixed airway lines between stations. The word 'function' here means 'what it does and how it works' — the operating purpose of the equipment, not a mathematical function.
Why Pilots Care
Enables more direct routes, reduces flight time, and increases flexibility in instrument flight rules operations.
Analogy
Think of the VOR/DME station as a known landmark on a map. If you know your direction and distance from that landmark, you can figure out where you are and navigate to another chosen spot nearby, even if that spot has no physical marker on the ground.
Grounding Statement
Picture a VOR station on the ground. Normally you can only fly directly to or from it. With VOR/DME RNAV, the box in your panel pretends the station is somewhere else — say, 20 miles north — and gives you guidance to fly to that imaginary spot instead.
Intuition Check
Do not assume VOR/DME RNAV is the same as GPS RNAV. VOR/DME RNAV is area navigation based on ground radio signals, while GPS RNAV is based on satellite position information.
Example Sentence 1
The chapter on the function of VOR/DME RNAV explains how the unit creates a waypoint by offsetting the signal from a ground station.
Example Sentence 2
By understanding the function of VOR/DME RNAV, the pilot can program the navigation computer to fly a route not aligned with published airways.