Definition
The default sensitivity setting of the Course Deviation Indicator (CDI) when a GPS-equipped aircraft is in the en route phase of flight, in which full-scale deflection of the CDI needle represents 5 nautical miles of lateral displacement from the desired course on either side of centerline.
Plain English
When you're flying between airports using GPS, the needle that shows whether you're left or right of your route is set to a wider scale: if the needle goes all the way to one side, you're 5 miles off course.
Context Anchor
Seen in GPS instrument approach discussions, especially when comparing en route, terminal, and approach CDI scaling.
Derivation
"En route" comes from French, meaning "on the way." In aviation, it refers to the cruise portion of a flight — between departure and arrival areas. "CDI" stands for Course Deviation Indicator. "Sensitivity" here describes how much course error it takes to move the needle a given amount.
Why Pilots Care
It sets the amount of course correction needed to stay centered and prevents unnecessary workload by using a scale appropriate for cruising distances.
Analogy
It is like using a map zoomed far out. Small movements on the display can represent large distances on the ground.
Intuition Check
Do not read “sensitivity” as a general description of how good the GPS is. Here it means the scale of the CDI needle: how many miles off course equal a full needle movement.
Example Sentence 1
While cruising at 9,000 feet, the GPS was in en route CDI sensitivity, so the half-scale needle deflection meant the aircraft was about 2.5 miles right of course.
Example Sentence 2
When the GPS sequenced to the terminal waypoint the CDI sensitivity tightened automatically from the en route value.