Flying IFR in the Mountains

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It’s the time of year when many are planning a flight to their favorite winter resort. Here are a few items to consider in addition to a good ski wax.

I’ve been privileged to fly the mountains of the southwest for more than 40 years—with many thousands of hours and more than 10,000 landings. But I’m not an expert, and I would be cautious of anyone who claims to be (Sparky Imeson comes to mind).

I have become reasonably proficient at understanding the risks of mountain flying and how to mitigate them. I’ll share a few of these as it is the season for the flat landers to head to the high country to enjoy their Nordic heritage.

Let me make a small but important distinction between high-elevation verses mountain airports. Santa Fe New Mexico (KSAF), and Centennial Colorado, (KAPA), are high-elevation airports (above 3000 feet MSL), but have no high peaks in the immediate vicinity. Aspen Colorado (KASE) and Angel Fire, New Mexico (KAXX) are mountain airports, above 3000 feet MSL, but nestled into valleys among significant mountains.

Mountain Weather

The first rule of thumb is to avoid IMC when flying into mountain airports—especially if you are a low-time instrument pilot. Bad weather is even “more bad” in mountainous terrain.

Winds are probably the most significant problem as the topography can accelerate velocities (venturi effect), and create vortices and downdrafts. Mountain waves, rotors and turbulence will not only challenge your piloting skills but ensure your passengers arrive with a new shade of green and a lap full of their last meal.

While five miles visibility might be OK in Oklahoma, unless you have at least 15 miles in the mountains (and forecast to stay that way) changes can occur rapidly especially in unsettled conditions. Mountains have a way of creating their own micro-climates. 

We are fortunate to have good weather reporting with remote AWOS systems being available in many mountain passes and unattended airports. Weather in the west has a high percentage of good flying days. But, make your schedule flexible so you don’t feel compelled to challenge Mother Nature.

Aircraft Performance  

Aspen Airport is way down there—in that valley. It's also way up there—field elevation is 7,838 feet.

We all know about density altitude and that the standard temperature at sea-level is 59° F (15° C). Unless your destination airport (which we’ll assume is at a modest 7000 foot MSL elevation) is reporting a cool 33° F, your plane will be performing as though at a higher altitude. Should this be a nice 85° summer day, your airplane will perform as though it is at 10,000 feet.

Filing IFR into some of the higher elevation airports in the western states will require that you can achieve MEAs of 16,000 feet. This is obviously an altitude that cannot be reached by most normally aspirated aircraft—assuming you do have oxygen for the requisite time at more than 12,500 feet.

If it sounds like I am being a pessimist—I am. Of course you would not want to be flying into an airport such as Aspen, Colorado (ASE) for the first time in IMC. After you have flown into a few of these interesting airports in day-VMC conditions, it should give you pause to attempt it in IMC. The proximity of the surrounding cumulo-granite is intimidating.

Even night VMC should give you second thoughts. Aspen requires that VFR pilots have accomplished a day landing in the preceding 12-months before attempting a night landing and night instrument approaches are prohibited.

Recall too that because of the altitude, your true airspeed will be greater by a factor of two-percent per thousand feet. Thus, landing at Aspen (elevation 7837) your approach speed will be almost 16-percent higher than what the ASI is telling you.

This can cause a noticeable difference in the timing from the FAF to the MAP. Fortunately, most of the airports in the mountainous regions have GPS and the timed approach is rare. 

Coupling this factor with the possibility that you may be landing downwind on a one-way runway, your speed control on final has to be precise.

Local Conditions

I operated out of Los Alamos, New Mexico (LAM) for 20 years. As mountain airports go, it is relatively easy. With a field elevation of 7171 feet, a restricted area south of the airport boundary, and a good size 10,441-foot mountain peak less than five miles to the west that dictates its one-way runway status. You land to the west (runway 27) and take-off to the east (runway 9). It is not uncommon to have the wind sock at either end of the runway pointing in opposing directions.

The LAM Instrument Approach Procedure takes advantage of a wide-open valley and provides two IAFs that lead-in either from the north or the south. Compared to Aspen’s 13,400-foot IAF, Los Alamos only requires 9500 feet—it’s a cinch. And the LAM MDA is reasonable 454 feet AGL and one-mile visibility, while KASE LOC/DME-E MDA is 2003 feet AGL and three miles.

My point is that not all mountain airports are created equal. You have to do a lot of homework to ensure you know the terrain surrounding the airport, the IAP and all of the notes and icons that provide additional information from the Airport Facility Directory—as well as the weather to be encountered. 

Note the extensive AIRPORT REMARKS that need to be considered when filing Aspen (ASE) as your destination. Special alternate minimums apply.

While LAM has a few restrictions (no circling approach for example) Aspen has a large list of items that include the requirement to get prior permission to use runway 15; that normal traffic patterns are not possible; and that high descent rates may be required.

The highest elevation airport in North America, is Leadville Colorado’s Lake County airport  (KLXV). At 9927 feet MSL, it also qualifies as a mountainous airport. Although it lies in an open valley, it has 14,000 foot peaks just five miles east and west. Departing IFR on DAVVY ONE requires a climb gradient of 364 feet-per-mile—550 fpm at 90 knots to 13,500 feet.

A Word to the Wise

With these few caveats, you can enjoy your time on the slopes. Plan your visit to do some sightseeing in another locale if you have to wait a day or so for the mountain airport to clear. And, if you consider my suggestions, we don’t even have to talk about icing.

While I used Aspen as an example, ten western states have airports that require mountainous considerations.

Ted Spitzmiller is a Gold Seal CFII, a FAASTeam representative and CAP member.

This article originally appeared in the November 2015 issue of IFR Refresher magazine.

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