Missing Transitions in Your FMS? Here’s Why… and What to Do

Why might approach transitions be missing from your FMS? If you’ve ever loaded an instrument approach and found that the expected initial approach fixes (IAFs) aren’t listed, you’re not alone. This month’s PIREP dives into why this happens, how the FAA codes can vary by approach, and what you need to know to avoid confusion when setting up for landing. Let’s break it down.

Figure 1 below shows the RNAV (GPS) Runway 18 approach to French Valley airport (F70). Note there are three Initial Approach Fixes (IAFs) shown on the chart (JESEX, KELTE, and TIQMU). 

Figure 2 shows the available FMS transitions when the approach is being loaded in the FMS. None of the IAFs are listed (JESEX, KELTE, or TIQMU). Only the feeder waypoints of CIVET, GAREY, and TANNR are shown. When one of the transitions is selected, the associated IAF and approach waypoints are then shown in the flight plan. So, why does this happen?

The reason this happens comes down to how approaches are structured and coded. While many approaches begin at an IAF, not all do. Some approaches use feeder routes to transition aircraft from enroute airspace to the approach phase. These feeder transitions—in Figure 2—act as entry points into the approach, which is why they appear in the FMS instead of the IAFs. 

Let’s recall that an approach can have up to five segments (Arrival Segment, Initial Approach Segment (IAF), Intermediate Approach Segment, Final Segment, and the Missed Approach Segment). Not all instrument approaches contain every segment. The arrival segment is a transition from the enroute phase to the approach phase of the flight. The initial approach segment begins at the initial approach fix (IAF) and ends at the intermediate fix. But looking at Figure 2, the loading approach transitions may or may not be the IAF. Pilots are used to selecting the IAF as the approach transition, as most approaches begin there—but not all do. 

So, what determines if they begin at the IAF?

Whether an approach begins at an IAF or a feeder route depends on several factors: geography, airspace design, and airport traffic flow. The FAA uses feeder routes to help manage arriving aircraft more efficiently in high-traffic areas or complex airspace. This also provides a smoother transition from enroute airspace to the final approach course, especially when multiple aircraft are arriving from different directions. In these cases, the FAA designs instrument approaches where aircraft begin their descent not at the standard IAF, but at a designated feeder route, ensuring a seamless transition from enroute airspace to the terminal area.

Adding to the confusion, some avionics manufacturers remove feeder transitions and start the approach at the IAFs.  However, when the FAA codes the approach this way, the feeder fix is still part of the approach, providing course, altitude and distance information to help support obstacle and terrain clearance. Once cleared for the approach, pilots can begin their descent to the depicted altitudes. Delaying descent until the IAF may cause excessive descent rates. 

FAA Form 8260, like the one shown below, describes how an approach is coded. They show leg types, distances, altitudes, transitions, IAFs, etc., and are available here. Select the IFP Documents Tab along the top. Page 1 shown in Figure 3 below shows JESEX, KELTE and TIQMU as IAFs. Page 9 in Figure 4 shows the available transitions of CIVET, GAREY and TANNR which is what is coded in the FMS. In addition to what gets coded in the FMS database, the Form 8260 includes chart information like the missed approach instructions, altimeter settings, temperature compensation, etc.

Next time you load an approach and the expected transitions aren’t there, you’ll know why—and more importantly, how to navigate it with confidence.

Program Pilot Derek Fiedler supports Honeywell Apex and radar for Flight Technical Services. He can be reached via email at FTS@Honeywell.com.