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It's getting dark, and you've never been here before. How can you get down safely?
This is Steamboat Springs, Colorado.
It isn't the toughest mountain airport to fly into. Especially when the weather's nice. But, it's surrounded by mountains - and it's high - at 6,882 feet MSL.
When you're flying into an airport like this, you need to do some solid descent planning to avoid the obstacles and terrain.
But you don't need to be in the mountains to find obstacles. You can find them here:
Steamboat is surrounded by mountains to the east and south. And we're coming in from the east, so we have a couple options for the descent.
The mountains we'll cross east of Steamboat range between 10,500' to 12,000' MSL, and Rabbit ears pass cuts through at 9600'. It's named for the two rocks that look like rabbit ears. They're actually the lava shafts from an ancient volcano.
The rabbit ears and the highway through the pass are generally easy to see. But, we're be coming in during the late afternoon, where terrain and the road may be hard to see.
On top of that, the mountaintop winds could be high. So we're going with option #2: flying an instrument approach.
Flying an instrument approach guarantees you terrain avoidance, and at an unfamiliar airport, it's often times your best choice. You get a pre-planned, easy to follow route guaranteeing you height above any obstacles along your flight path. And, you get a descent profile to help you get down.
Steamboat has two approaches: the VOR/DME C and the RNAV GPS E. Both are non-precision, but we'll fly the the GPS. Its minimum descent altitude is a little lower, by 160 feet. But, since the weather is clear, that won't make a huge difference for us.
The big advantage here is simplicity. The Cirrus Perspective avionics will draw a glide path as we descend from our enroute altitude to the final approach fix. The feature is called VNAV, for "Vertical Navigation" - and many WAAS enabled GPS systems have this capability. And with it, we can make a smooth descent through each step down fix without leveling out. Which is more comfortable, and requires fewer power adjustments.
Most aircraft don't have VNAV capability though, but not much changes. Instead of a smooth descent, you can descend down and level off at each segment altitude. You still get the same obstacle protection, it's just a little higher workload. Or, you can calculate a descent rate to simulate VNAV.
When we reach our minimum descent altitude, we're still left with a problem. The approach takes us down to 7980' MSL, which is 1100' feet above the airport. That's higher than pattern altitude, which is 7900' MSL.
If we fly a constant angle from our final approach fix past our step down fixes, we're left with a 7.75 degree descent angle. And that's not a little above 3 degrees. That's a 1,365 foot-per-minute descent rate at 100 knots. And that' a lot of ground rush.
So we have a couple options to overcome the steep descent. First, we can overfly the runway and enter the traffic pattern. It's the definition of a true circling approach, and it can help us set up for a good landing by allowing us to use standard speeds and power settings.
Our second option? We can descend down once we're visually clear of the obstacles to join a normal glidepath. It's not the easiest solution, partially because the PAPI on runway 32 is out of service.
But we're taking this option today, because it shows just how difficult a steep approach can be.
As we're coming in, we're picking up a common winter visual illusion. Especially when there's low light. Is that a hill or a drop-off just before the runway? It's hard to tell with no color variation because of the white snow and the low light.
If it was a hill, it may be hard to avoid until we're too close. But, from past experience and from the airport directory, we know it's a drop-off.
Which leaves us with our second illusion. The black hole effect. We can clearly see the runway. We can read the numbers and pick out the centerline. But, with the bright mountains lit up by the sunset, the dark runway looks like a black hole. Which leads to a common nighttime landing illusion: flaring too high.
So what can you take from this? Because you may never fly into Steamboat Springs. Depending on where you live, you may never fly into any mountainous airport.
You don't need mountains to fly near terrain and obstacles: hills, buildings, trees - they'll all do fine.
Maybe it's a reason to get your instrument rating - shooting an approach into an airport when the terrain's unfamiliar and it's getting dark is always a good idea.
And maybe it's a reason to fly a standard traffic pattern instead of a straight in approach. It's a lot easier to make that 3 degree glide slope work out. And everyone loves a soft landing.
Aleks is a Boldmethod co-founder and technical director. He's worked in safety and operations in the airline industry, and was a flight instructor and course manager for the University of North Dakota. You can reach him at firstname.lastname@example.org.