Definition
An RNAV path-and-terminator leg type that begins at a defined fix and continues along a specified track until a designated along-track distance is reached. The leg terminates when the aircraft has flown the prescribed distance from the originating fix, regardless of altitude or other conditions.
Plain English
A coded segment of an RNAV procedure that tells the aircraft to fly from a starting point along a set heading or track for a specific distance, then end at that distance.
Context Anchor
Seen in instrument procedure coding and flight management system route logic, especially when studying path-and-terminator legs.
Derivation
The two-letter codes used in path-and-terminator leg types follow a consistent pattern: the first letter describes the path, the second describes the terminator. 'F' stands for Fix (the starting point) and 'D' stands for Distance (what ends the leg). So FD literally reads as 'from a Fix, terminating at a Distance.'
Why Pilots Care
Allows procedure designers to create precise termination points using existing ground-based distance equipment without requiring an additional fix.
Intuition Check
Do not read “FD” as flight director here. In path-and-terminator leg coding, FD means Fix to DME distance.
Example Sentence 1
The departure procedure uses an FD leg to take the aircraft three miles past the airport reference point before turning on course.
Example Sentence 2
After crossing the fix, the aircraft follows the FD leg until reaching the specified DME distance.