When To Go Missed
Aspen, Colorado (ASE)
The airport sits at 7,837 feet above sea level, with towering mountains peaking at over 14,000 feet just a few miles away. The runway is snuggled in a box canyon, with one way in and one way out. Not only must you have a heightened situational awareness, but adequate advanced
planning, too.
Typically, for non-precision approaches, the Missed Approach Point (MAP) is noted in the
profile view. Here, it is CEYAG or I-ASE 4 DME. This puts you 2,100 feet above the
touchdown zone with 2.6 nautical miles from the runway. Some quick math puts this glide path at around 808 feet per nm — a plus-nine-degree slope! This is a very steep approach. It is
probably best to calculate a visual descent point (VDP). (See my last article.)
A three-degree glide slope at an altitude loss of 2,003 feet requires about 6.7 nm from the
threshold. This would mean starting the approach to the runway ***before*** the Final
Approach Fix (FAF) of DOYPE. While a three-degree glide slope is ideal, it is unlikely to occur for this approach given the terrain profile and step-down limitations. To adapt, we could increase the slope. But remember: We must satisfy 91.175(c) for Part 91 operations, where the aircraft must be in a continuous position from which a descent to land on the intended runway can be made using normal maneuvers.
To maintain the aircraft in such a position, the approach slope of 6.59 degrees (as suggested on the plate) would have to begin about five nm from the threshold, or 6.4 DME from I-ASE. This would begin just ***after*** the FAF.
If you can’t see the runway by five nm from the threshold or 6.4 DME from I-ASE, you might expect to go missed, because descending to the runway at your MAP may not satisfy 91.175(c) — or even your aircraft’s capabilities. Note that if you are to leave the MDA altitude after the FAF, you must meet all three criteria of 91.175(c).
Environmental Considerations
This approach to Runway 15 typically includes a tailwind component, like mountain valley winds or katabatic winds, for example. Tailwinds will increase the aircraft’s ground speed,
therefore increasing the rate of descent required.
Questions to Ask Yourself:
Can your aircraft perform to this steep approach? Does your aircraft have a Terrain Awareness and Warning System (TAWS)? Could the high sink rate alert come on during this approach? Will you shut off this warning system to perform this approach? If you do shut off this warning system, wasn’t it trying to protect you?
While this approach into Aspen looks straight forward on where to go missed, it would be better to expect to go missed if you can’t see the runway from the FAF, and/or the rate of descent
exceeds your/the aircraft’s limits. Having the plan to go missed at a certain point will reduce workload while flying this task-heavy approach.
Advanced Planning:
Did you calculate your required rate of descent and ground speed? What descend rate will
exceed a stabilized approach for your aircraft? Where is the MAP, or at what point do the
aircraft’s capabilities limit you from performing this approach safely and/or legally? Were you ready to go missed from the start of this approach?
If you plan for a missed approach on every approach, then you’ll never be surprised that you had to push the shiny throttle levers forward.
