Definition
An RNAV path-and-terminator leg type that defines a straight, geodesic flight path between two fixes, with the leg terminating at a named initial fix (IF). It is used to define the start point of an RNAV procedure or to connect segments without specifying a course or distance other than the path between the two fixes.
Plain English
A coded segment in an RNAV procedure that simply tells the aircraft to fly directly from one named point to another, ending at the initial fix that begins the next part of the procedure.
Context Anchor
Seen in RNAV procedure coding, avionics flight-plan legs, and instrument procedure design discussions.
Derivation
Initial' comes from the Latin initialis, meaning 'at the beginning.' In procedure design, the initial fix is literally the fix where a procedure or segment begins — the starting waypoint the aircraft must reach before continuing.
Why Pilots Care
It sets the exact entry point into a procedure segment, ensuring correct lateral navigation and leg sequencing.
Intuition Check
Do not read “IF” as an if-then condition. Here, IF means initial fix: the named starting point for the next coded part of the procedure.
Example Sentence 1
The RNAV approach begins with an IF leg from WILBO to the initial fix at CRAFT, where the aircraft joins the published approach.
Example Sentence 2
The database coded the procedure with an IF leg at the first waypoint to establish proper course guidance.