Every instrument approach procedure is built around a series of defined fixes that guide you from the en-route environment all the way to the runway environment. Three of those fixes—the Initial Approach Fix (IAF), the Intermediate Fix (IF), and the Final Approach Fix (FAF)—each serve a different purpose in a carefully choreographed descent. Confusing them on the FAA knowledge test costs points; confusing them in actual IMC can cost lives. This article walks through what each fix is, how they relate to one another, and what you are expected to do at each one.
The architecture of an instrument approach is defined in the FAA's Instrument Procedures Handbook (FAA-H-8083-16) and the Instrument Flying Handbook (FAA-H-8083-15). The underlying legal framework comes from 14 CFR Part 97, which prescribes standard instrument approach procedures (SIAPs). Every published approach chart you fly is built on this foundation.
The Initial Approach Fix (IAF)
The IAF is the starting gate of the approach sequence. It marks the point where you transition from the en-route or terminal phase of flight into the initial approach segment. On a published approach chart, IAFs are labeled with the text (IAF) next to the fix name. An approach may have multiple IAFs, each designed to funnel arriving traffic from different directions or from different arrival routes onto the same approach path.
When you cross the IAF, you should already be configured for approach operations: ATIS received, approach briefed, altimeter set, and frequencies tuned. The initial approach segment itself begins at the IAF and ends at the IF (or, on some approaches, directly at the FAF if there is no distinct IF). During this segment you are expected to maneuver—possibly flying a procedure turn or a holding-in-lieu-of-procedure-turn (HILPT)—to align yourself with the final approach course and to lose altitude in a structured way.
Altitude at the IAF is governed by the published Minimum En Route Altitude (MEA) or Minimum Sector Altitude (MSA) and the altitudes printed on the approach chart. The IAF altitude is typically higher than the intermediate segment altitude, and the descent from it is gradual and deliberate. ATC may issue a "cleared for the approach" instruction while you are still some distance from the IAF, but you do not begin the approach procedure itself until you reach the IAF.
The Intermediate Fix (IF)
The IF marks the boundary between the initial approach segment and the intermediate approach segment. Its job is to give you a stabilization zone—a stretch of relatively level flight where you get the aircraft configured, speed stabilized, and mentally prepared before you commit to the final descent. The Instrument Procedures Handbook describes the intermediate segment as the phase where the aircraft's configuration, speed, and positioning are refined in preparation for the final approach segment.
On many approach charts, the IF is collocated with the point where a procedure turn or HILPT is completed, or where a feeder route intersects the final approach course. The intermediate segment is normally designed to be between 5 and 10 nautical miles in length and is flown at a constant altitude (the intermediate segment altitude shown on the chart). You should not be descending during this segment unless the chart specifically depicts a stepdown fix within it.
Not every approach has a separately depicted IF. On simpler procedures the initial segment transitions directly to the final approach segment at the FAF. When an IF is depicted, however, it is a critical checkpoint: crossing it means your speed should be at or near your final approach speed, flaps should be in the approach setting, and checklist items should be complete. Think of the IF as your last chance to get organized before the real work begins.
The Final Approach Fix (FAF)
The FAF is arguably the most operationally significant of the three fixes. It marks the beginning of the final approach segment—the point from which you begin the final, continuous descent toward the runway (or the missed approach point if the runway environment is not in sight). Crossing the FAF is the trigger for starting your timer on non-precision approaches and beginning your descent from the intermediate altitude; final configuration, including gear extension, is normally completed prior to or at the FAF rather than triggered by crossing it.
On precision approaches (ILS, GLS), there is no charted FAF; instead, the point of glide slope intercept on the final approach course—sometimes called the Precision Final Approach Fix (PFAF)—is identified on the chart by a lightning bolt symbol. Once established on the glide slope, the glide slope itself guides your descent—the FAF simply confirms you are in the right place at the right altitude to follow it.
On non-precision approaches (VOR, NDB, LOC, RNAV/LNAV), the FAF is depicted by a Maltese cross symbol on the profile view of the chart. At the FAF you descend from the intermediate or step-down altitude to the Minimum Descent Altitude (MDA) and then fly level at the MDA until you either see the runway environment or reach the Missed Approach Point (MAP). Timing from the FAF to the MAP—using the time/distance table on the chart—tells you when to execute the missed approach if you have not acquired visual contact.
The altitude at the FAF is critically important. Descending below the FAF altitude before reaching the FAF is a classic error that can place you below obstacle clearance surfaces. Conversely, arriving at the FAF above the charted altitude on a non-precision approach means a steeper-than-normal descent to the MDA, which can destabilize the approach.
How the Three Fixes Work Together
Picture the three fixes as a funnel. The IAF is the wide mouth—you enter it from many possible directions, often flying a procedure turn or arc to get aligned. The IF narrows the funnel—you are now on the correct course, at the correct altitude, configured and stabilized. The FAF is the narrow end—you commit to the final descent and are fully established. This progression is intentional: each segment is designed so that workload is distributed rather than piled up at the last moment.
In a practical cockpit scenario flying a VOR approach: you cross the IAF (a VOR station, for example) at 4,000 feet, fly the procedure turn to reverse course, track inbound, and cross the IF (where the procedure turn is completed) at 3,000 feet with gear down and approach checklist done. In this hypothetical example, you cross the FAF at 2,200 feet, start your timer, and descend to an MDA of 1,460 feet. At the MAP—determined by your timer or a fix—you either land or execute the missed approach.
Key Numbers and Rules
- IAF: Labeled (IAF) on charts; begins the initial approach segment; may be multiple per approach; procedure turns and HILPTs are associated with the initial segment.
- Intermediate segment length: Ideally at least 5 NM to allow aircraft stabilization; flown at a constant altitude unless stepdowns are charted.
- FAF on precision approaches: Identified by a lightning bolt symbol; corresponds to glide slope intercept altitude.
- FAF on non-precision approaches: Identified by a Maltese cross (✝) on the profile view; begin descent to MDA here and start timing.
- Timing: On non-precision approaches, start the clock at the FAF; use the chart's time/distance table to identify the MAP.
- Altitude discipline: Do not descend below the published altitude for each segment until you have crossed the fix that authorizes the next lower altitude.
- "Cleared for the approach": ATC clearance authorizes you to execute the full procedure beginning at the IAF; it does not mean begin descending immediately.
Common Test Traps
- Confusing the Maltese cross with the lightning bolt: The Maltese cross marks the FAF on non-precision approaches; the lightning bolt marks the FAF on precision approaches. The test will ask you to identify which symbol applies.
- Starting the timer at the wrong point: On non-precision approaches, timing begins at the FAF—not at the IAF or IF. Starting too early makes the MAP appear to arrive too soon; starting too late may cause you to fly past the MAP.
- Assuming every approach has all three fixes: Some simple procedures merge the IF and FAF or omit a separate IF entirely. Always read the chart rather than assuming a standard structure.
- Descending before reaching the authorizing fix: Each fix authorizes a lower altitude. Descending early places you below obstacle clearance surfaces and is a common cause of controlled flight into terrain (CFIT) on approach.
- Multiple IAFs and procedure turns: When ATC vectors you to final, they eliminate the procedure turn—you may be cleared to intercept the final approach course at a point other than the IAF. In that case, the intermediate and final segments still apply, but the initial segment (and any associated procedure turn) is bypassed. Understand that the published procedure turn is not required when ATC provides radar vectors to final.