Definition
A TF (Track to Fix) leg is an RNAV path defined as a geodesic (great-circle) track between two named waypoints. The aircraft flies a precise, fixed track from a defined starting waypoint to a defined ending (terminator) waypoint, regardless of wind. TF is the preferred RNAV leg type for straight segments because both endpoints and the desired track between them are explicitly coded in the navigation database.
Plain English
A straight, locked-in path between two named points on a GPS route. The system knows exactly where the line starts, where it ends, and the exact track to follow between them.
Context Anchor
Seen on RNAV instrument procedures and in GPS or flight management system leg sequences.
Derivation
The name describes the function: 'Track to Fix' means follow a specific track until reaching a fix. Path-and-terminator leg names in the ARINC 424 navigation standard always work this way -- the first letters describe the path flown and the last letter describes what ends the leg. Here, T = Track, F = Fix.
Why Pilots Care
TF legs give the most predictable, repeatable ground track of any RNAV leg type, which is why they are used wherever possible for straight segments of an instrument procedure. Knowing your aircraft is on a TF leg tells you the path is fully defined end-to-end and the autopilot or GPS will hold a precise track, not just point at the next waypoint.
Analogy
It is like drawing a line on a map from one marked point to another, then following that line until you reach the second point.
Intuition Check
Do not read “track” here as just the direction the nose is pointed. In a TF leg, the important thing is the path over the ground from one fix to the next.
Example Sentence 1
Most of the straight segments on this RNAV approach are coded as TF legs, so the FMS will hold a consistent ground track between each waypoint.
Example Sentence 2
The FMS sequences the TF leg automatically once the aircraft passes the prior waypoint.