Definition
A mode selection on a VOR/DME RNAV unit that configures the system for approach operations, providing increased course sensitivity (typically full-scale deflection at 1.25 NM each side of course) for precise tracking to a waypoint during an instrument approach.
Plain English
A setting on the navigation unit that tells it you are flying an approach, so it tightens up the course needle to give you finer left-right guidance when you need to be very accurate near the runway.
Context Anchor
Seen on older VOR/DME RNAV control panels or mode selectors when setting up the equipment for an RNAV approach.
Derivation
RNAV stands for Area Navigation, meaning navigation along any desired path rather than only directly between ground stations. APPR is short for Approach. Together the label tells the pilot the unit is in the high-sensitivity mode used for the approach phase.
Why Pilots Care
RNAV approaches provide vertical and lateral guidance to many airports that lack an ILS, increasing access in lower weather conditions.
Intuition Check
Do not read RNAV/APPR as two separate tasks to choose between. In this context it means RNAV approach mode: area navigation guidance being used for an approach.
Example Sentence 1
After crossing the initial approach fix, the pilot switched the RNAV unit to RNAV/APPR to get finer course guidance toward the final waypoint.
Example Sentence 2
With the autopilot coupled in RNAV/APPR, the aircraft began its descent at the calculated vertical path angle.