Definition
The Initial Approach Fix is the charted point where the initial segment of an instrument approach procedure begins. It marks the transition from the en route or arrival phase into the structured approach to a runway, and is identified on approach charts by the label IAF next to the fix.
Plain English
The official starting point of an instrument approach. When you cross this point, you stop being in the en route phase and begin flying the published approach toward the runway.
Context Anchor
Seen on instrument approach charts and in clearances that tell a pilot where to begin the approach.
Derivation
Fix in aviation comes from the older navigational sense of 'fixing' your position — establishing exactly where you are using a known reference. An Initial Approach Fix is therefore the first known position that anchors the start of the approach.
Why Pilots Care
It tells the pilot and controller exactly where the approach phase begins, ensuring correct navigation setup and traffic separation.
Intuition Check
Do not assume the IAF is simply the first point the pilot happens to fly to. In this context, it is a published point that begins a defined part of the instrument approach.
Example Sentence 1
Cleared direct to the IAF, the pilot began descending to the published initial approach altitude.
Example Sentence 2
ATC cleared the aircraft direct to the IAF for the ILS runway 27 approach.