Could somebody explain what RNAV is please?
RNAV is the technique of using positioning data to allow an aircraft to follow a pre-determined flightpath with a particular degree of accuracy.
Instead of following a course defined by conventional ground navaids - which might involve flying an inefficient flightpath - an aircraft in RNAV airspace can fly more directly from A to B by using its own on-board navigation systems to keep it on track.