High terrain also presents some unique considerations when flying on instruments. For example climb gradients, visual descent points, and abnormal instrument procedures.
One such scenario involves what to do if you need to go missed after a missed approach point, i.e. on a visual descent leg.
To understand this scenario you’ll need to look at the approach chart ILS-06 for Gunnison Colorado (KGUC). You’ll see that the DH is 8590 (minimum) which will be roughly a distance of 2.4 miles from the runway at an altitude of 923 feet. The basis for this potential scenario is based on the fact that a lot can happen in 2.4 miles and 923 feet.
Let’s imagine you fly this approach and arrive at the DH, you see some portion of the runway environment and continue to descend for landing. Now at 350 feet and 1 mile the wind picks up and you completely loose sight of the runway due to the increased blowing snow. What would you do now? Most pilots would answer that they would go missed. While this is conceptually the right answer (since continuing the descent is no good), the details of how to carry out this missed approach procedure needs to be explored.
See, the missed approach procedure is designed to be flown from the missed approach point or decision height… not before or after. As part of instrument training, we teach our students that if they decide to fly missed before the missed approach point they can begin climbing immediately, but they need to wait to turn until after the missed approach point. Executing the procedure before or after the MAP/DH may place the aircraft in danger, especially in mountainous terrain where the missed lateral track is designed to keep the aircraft clear of specific terrain.
Today, the missed procedure for GUC is climb straight to 10,000 then climbing right turn HDG 180 to 12,000. When this approach was originally first published, the missed procedure was climbing right turn to 12,000. If the pilot attempted to fly the missed past the DH, then there was a good chance they would hit a mountain to the right – this was later revised to include the straight ahead portion to 10,000.
Back to our sceanrio, what does a pilot do if they need to fly missed past the MAP or DH? The first solution is to avoid getting in this situation to begin with. As part of the preflight excercise the pilot should be carefully reading the approaches to the destination airport as well. If the approach has a DH or MAP that is more than a half mile from the runway then the pilot should consider whether this type of scenario could develop, and what should be done if it does develop.
If the approach DH or MAP is more than a half mile ask yourself if the executing the missed approach after the DH will create any potential hazards. If so, then take a look at the departure procedure for that runway. How does the departure procedure work? You might find that if you fly past the DH or MAP and need to go missed the better procedure to follow may be the departure procedure or SID for that runway.