Definition
An RNAV path-and-terminator leg type that begins at a defined fix and continues along a specified course until the pilot or controller manually terminates it, typically by selecting the next leg or receiving a vector instruction. The leg has a defined starting point and course but no predetermined endpoint coded into the procedure.
Plain English
A flight path that starts at a known point and follows a set heading or course until someone — usually ATC or the pilot — tells the aircraft when to stop flying it and move on to the next part of the procedure.
Context Anchor
Seen in instrument procedure coding and GPS or flight management system flight plans, especially when a leg cannot be ended by a normal automatic point.
Derivation
The two-letter code 'FM' follows the ARINC 424 path-terminator naming convention, where the first letter describes the path type ('F' = from a fix) and the second describes how the leg ends ('M' = manual termination). Knowing the code structure helps decode any path-terminator type without memorising each one individually.
Why Pilots Care
Pilots need to know when an FM leg requires manual termination so the aircraft does not continue past the intended point.
Grounding Statement
An FM leg is a built-in pause in automatic navigation: it continues until the pilot takes action.
Intuition Check
Manual termination does not mean the pilot must hand-fly the airplane. It means the navigation system needs a pilot command before it stops that leg and goes to the next one.
Example Sentence 1
After departure, the aircraft flew the FM leg outbound from the fix until ATC issued a vector to join the en route structure.
Example Sentence 2
The missed approach begins with an FM leg that the crew terminates once visual conditions are established.