Navigating Missed Approaches: Understanding System Limitations and Procedure Design

You’re likely familiar with standard instrument departure procedures: unless otherwise noted, you should be above 35 feet AGL by the time you reach the departure end of the runway (DER), avoid turning below 400. feet AGL, and maintain a climb gradient of at least 200 feet per nautical mile. These guidelines ensure safe separation from obstacles and terrain during departure.

You’re likely familiar with standard instrument departure procedures: unless otherwise noted, you should be above 35 feet AGL by the time you reach the departure end of the runway (DER), avoid turning below 400. feet AGL, and maintain a climb gradient of at least 200 feet per nautical mile. These guidelines ensure safe separation from obstacles and terrain during departure.

A quick look at the plan view shows significant terrain in the area. The missed approach notes  also specify a non-standard climb gradient of 270 feet per nautical mile up to 7,700 feet, making terrain clearance a critical factor.. 

This procedure has a Visual Descent Point (VDP)—a defined point on a straight-in, non-precision approach where a pilot can descend below the MDA, as long as you have the required visual reference. If a VDP is available, it will be indicated by a "v" on the profile view portion of the instrument approach procedure chart. Crucially, pilots should not descend below MDA before reaching the VDP. 

The FAA codes procedures using ARINC-424 leg types, commonly referred to as PATH-TERMINATOR legs because they define both the flight path and what brings it to an end. For example, Course to a Fix (CF) and Radius to a Fix (RF) leg types. For this procedure, we are interested in (4) leg types:  

• Track to a Fix (TF)
• Course from a Fix to an Altitude (CA)
• Direct to a Fix (DF)
• Hold to a Manual Termination (HM)

And finally, let’s break it down with some math. A 3° descent path requires 318 feet per NM which we usually round to 300 feet per NM. Here we have a 3.5° descent path, increasing the descent rate to 371 feet per NM. 

Looking at the chart in Figure 1, the procedure should be flown to the VDP point which corresponds to the Minimum Descent Altitude (MDA) of 6,480 feet. However, since this was a VFR day, the crew likely continued descending all the way to the missed approach point, WINUB. If they maintained a 3.5° descent path, they would have descended an additional 260 feet (0.7 × 371), bringing them to 6,220 feet. At this point, the FMS was simply following coded instructions. So, let’s break down those instructions: 

• At YAKYU, the aircraft follows a Track to Fix leg (YAKYU-WINUB) leading to WINUB. 
• WINUB is coded as both a flyover waypoint and a missed approach waypoint. 
• After WINUB, the next instruction is a Course to Altitude leg (CA), directing the aircraft to fly a course of 182° until reaching 6,300 feet.
• Once the aircraft reaches 6,300 feet, the next instructions command a right turn onto a Track to a Fix leg to GRIOT, followed by a Direct to Fix(DF) leg to AWEGA, where the aircraft enters a hold.

In this case, when the aircraft reached WINUB, it was at 6,220 feet. However, the FMS was programmed to climb on a course of 182° until reaching an altitude of 6,300 feet  before initiating the right-hand turn. 

If the crew had initiated the missed approach at the VDP— which corresponds to the MDA of 6,480 feet—or even slightly after, they would have been above the required 6,300 feet and able to turn as expected. 

Where does the 6,300-foot requirement come from? It follows the standard rule of no turns below 400 feet AGL. Given the airport elevation of 5,904 feet, adding 400 feet brings the total to 6,304 feet, which is rounded down to 6,300 feet.

If you check your flight plan (Figure 3), all of this information is there, it’s just a matter of thinking like the FMS and understanding how it processes instructions.