Definition
A display page on an FMS or GPS navigator that shows the sequence of flight plan legs currently being flown, with the leg the aircraft is presently navigating highlighted as the active leg. It lists each leg's path terminator, course, distance, and associated waypoints in the order they will be flown.
Plain English
The screen on the aircraft's navigation computer that shows the list of legs in the current flight plan and which one the aircraft is flying right now.
Context Anchor
Seen when loading, checking, or flying an RNAV departure, especially before takeoff and during the first turns or course changes after departure.
Derivation
"Leg" in navigation means a single segment of a route between two points. "Active" here means the segment currently being flown. So the active legs page is the page showing the legs that make up the live flight plan.
Why Pilots Care
Allows the pilot to confirm the aircraft is following the correct route and to anticipate upcoming turns or altitude changes.
Intuition Check
Do not read “legs” as anything physical on the airplane. Here, a leg is one route segment from one navigation point to the next, and “active” means the navigation system is using that segment now.
Example Sentence 1
Before takeoff, the captain pulled up the active legs page and confirmed each waypoint in the RNAV departure matched the clearance.
Example Sentence 2
During the departure the active legs page showed the turn at the first fix and the distance to the second.