Definition
The combined inaccuracies that affect a VOR/DME-based area navigation (RNAV) position solution. Because a VOR/DME RNAV computer derives the aircraft's position from a single VOR/DME station's bearing and slant-range distance, any error in the VOR signal, the DME signal, the airborne receiver, the computer, or the geometry between aircraft and station is carried into the computed waypoint position and the resulting course guidance.
Plain English
RNAV that uses a VOR/DME station to figure out where the airplane is will only be as accurate as that station and its signals. Small errors in the bearing, the distance, or the math the box does to combine them all add up and shift the airplane's computed position away from where it actually is.
Context Anchor
Seen in instrument flying when using older RNAV equipment that builds routes or waypoints from VOR and DME information instead of relying only on GPS.
Derivation
Error comes from a Latin word meaning “to wander.” That fits this use: the indicated position or course can wander away from the aircraft’s actual position or intended path.
Why Pilots Care
Recognizing these errors prevents the pilot from accepting an incorrect position that could lead to airspace violations or unsafe terrain clearance.
Analogy
It is like drawing your position on a map from two measurements. If either measurement is a little off, the point you mark on the map will also be a little off.
Intuition Check
An “error” here does not always mean the pilot made a mistake. It means any difference between the navigation information shown and the aircraft’s true position or intended path.
Example Sentence 1
At 80 NM from the reference station, the instructor reminded the student that VOR/DME RNAV errors increase with distance, so course deviations should be cross-checked against another source.
Example Sentence 2
During the briefing the instructor pointed out how VOR/DME RNAV errors grow larger as distance from the stations increases.