Definition
A path-and-terminator leg type used in RNAV procedure coding that defines a direct course from the aircraft's current position to a specified fix, with no defined inbound track. The leg begins wherever the aircraft is when the leg becomes active and terminates at the named fix. It is commonly used after a runway-aligned departure leg or following a flyover waypoint, where the starting position is variable but the endpoint is fixed.
Plain English
A leg that simply says 'go straight to this point from wherever you are right now.' The starting point depends on where the aircraft happens to be; the ending point is a fixed, named location.
Context Anchor
Seen in RNAV instrument procedure design and in discussions of path and terminator legs used by navigation systems.
Derivation
The 'DF' code comes from ARINC 424, the industry standard for coding navigation database procedures. Each two-letter code names a leg type: 'D' for Direct, 'F' for Fix. So DF literally reads as 'Direct-to-Fix.' Knowing the coding scheme helps when reading procedure design documents or troubleshooting how an FMS flies a published procedure.
Why Pilots Care
It ensures accurate sequencing to the fix for obstacle clearance and procedure compliance.
Intuition Check
Do not read “fix” as a repair. In this context, a fix is a specific named location used for navigation. Do not read “leg” as the whole flight. Here it means one segment of the procedure.
Example Sentence 1
After the runway heading climb, the SID transitions to a DF leg that takes the aircraft directly to WAYPT regardless of where the climb ends.
Example Sentence 2
After departing the hold, the aircraft flew the DF leg directly to the final approach fix.