Definition
A Changeover Point that is not located at the midpoint between two VOR navigation aids defining a Federal airway or jet route segment. When the COP is not at the midpoint, it is depicted on the en route chart with a mileage figure showing the distance from each station, indicating where the pilot must switch navigation reception from the station behind to the station ahead.
Plain English
On most airway segments, you swap from tuning the VOR behind you to the VOR ahead of you at the halfway point. An offset COP is a switch point that is not at the halfway mark — it sits closer to one station than the other, and the chart shows you exactly how far it is from each.
Context Anchor
Seen on instrument en route charts and in discussions of when to switch from one navigation reference to the next along an airway or published route.
Derivation
Offset' comes from the idea of being shifted away from a normal or expected position. Here, the COP is shifted away from the standard midpoint location between the two stations.
Why Pilots Care
An offset COP prevents loss of navigation signal due to terrain, distance, or facility limitations, maintaining accurate course guidance throughout the segment.
Intuition Check
Offset does not mean the route itself moves sideways. Here it means the changeover point is shifted along the route away from the normal halfway point.
Example Sentence 1
The chart showed an offset COP 32 miles from the station behind and 18 miles from the station ahead, so the pilot retuned the second VOR earlier than the segment midpoint.
Example Sentence 2
Because of intervening terrain, the offset COP on this airway requires changing over well before the halfway point between the two facilities.