Approach Treachery

Approaches to some airports are challenging enough under the best conditions, but low weather makes them deadly


Aspen, Telluride, Hayden, Jackson, Sun Valley, Missoula, Ketchikan, Juneau.

These beautiful locations have some of the most treacherous instrument approaches found anywhere in the United States for one simple reason: big mountains. It will be many months before the NTSB issues its final report on the fatal accident of the Gulfstream that crashed during its final approach into Aspen on March 29, and the preliminary report it issued shortly after the crash contained less information than the local newspaper.

To state that the instrument approaches into these locations are tricky is an understatement. As a former EMS and fire-fighting pilot operating into all of these airports, I can tell you that I almost break out in a sweat when I think about night or bad weather operations in these locations.

The immensity of the risks involved with instrument approaches into these locations is difficult to overstate.

The mountainous terrain influences every aspect of aviation operations into and out of places like Aspen. Unlike relatively flat country where the instrument approach designers were able to design an instrument approach with plenty of clearance from obstructions, the narrow valleys and steep mountainsides at these locations are very confining for both VFR and IFR operations.

Just about any instrument pilot has shot through a localizer, which in flat terrain is usually a non-event. The radar controller probably saw the excursion on radar and provided a vector back to the course. About the only hazard associated with overshooting the final approach course in flat terrain may be penetrating an approach course for a parallel runway at busier airports, but it is unlikely that you will hit anything.

In the mountains, however, if you overshoot the approach course or turn the wrong direction, you will come face to face with a wall of granite. There simply is no room for deviating from the course lines in this type of terrain.

Even the en route structure over some of these locations is non-radar, meaning that you are missing a very vital set of eyes in the form of an ATC controller to keep you away from the rocks. The Flight Safety Foundation has determined from accident data that being in a non-radar environment significantly increases your chances of a controlled-flight-into-terrain accident.

At night or in IMC, its impossible to get a good mental picture of the terrain if you are unfamiliar with the location. Its one thing to see the pictures of Jackson and know that mountains exist around there, but until you fly the instrument approach in visual conditions, you wont realize just how close those rocks come to the wing of your aircraft when you arent exactly on the centerline of the approach.

You must have a reliable navigation signal before you descend on an approach in this type of terrain. You must have the correct course dialed into the navigational instrument. You must have a properly calibrated navigation receiver that has been recently checked for the accuracy of its signal.

Once you have complied with these precautions, its highly advisable that you remain on the centerline. If possible, have a copilot with a separate set of charts backing you up on the selection of courses and maintaining an awareness of deviations from the centerline of these approaches. Although Jeppesen approach plates now have threatening topography shaded to help the pilot form a mental picture of the surrounding terrain, its still tough to form a complete mental picture of the terrain from a flat piece of paper.

Many commercial operators have declared these airports to be special qualification airports, requiring the aircrews to undergo special training prior to operating there. For instance, some operators have films of the approach into the location to show the nearness of the mountains and to impress upon the pilot the need to keep track of the airplanes relationship with the terrain at all times.

The films graphically illustrate the missed approaches at these locations, which by the way, are pretty hairy if you delay executing the procedure. The commercial operators also have graphs, charts and special procedures in order to assure terrain clearance. Its fairly common for the operators to require a check airman to sign off the pilot during actual flights into these locations.

Of course these types of safeguards are not mandated in Part 91. It is the pilots (or operators) right to execute the instrument approach into these locations without any prior experience. Executive Jet Aviation, the nations largest operator of business aircraft, does not permit its pilots to make night approaches – visual or instrument – into Aspen.

Ironically, an FDC NOTAM was issued just days before the Gulfstream accident. The FDC Notams for Aspen stated the VOR DME or GPS-C Approach was no longer authorized at night. Official sunset on the accident date was 18:28 and night time started at 18:58. The Gulfstream III is a Category D aircraft when conducting non-precision or circling approaches. Category D aircraft are not authorized to fly this approach at any time, day or night.

The published instrument approach procedure at Aspen states: Terrain will not allow for normal traffic patterns. High rates of descent may be required due to terrain and local procedures. Airport located in high mountain valley with mountainous terrain from 12,500 to 14,000 MSL in proximity to airport; numerous obstructions. All adverse weather situations magnified in mountains. Unless ceilings are at least 2000′ above highest terrain and visibility is 15 miles or more; mountain flying is not recommended.

Dont be surprised to discover that the descent rate on all segments of the approaches into these kinds of airports seems rather steep. It has to be.

For the approaches into Jackson, Wyo., for example, the MEAs leading into the VOR are as high as 15,000 feet. From 15,000 feet on the airway, you somehow have to lose enough altitude to land on a runway that sits 6,445 feet MSL. Losing more than 8,500 feet takes some maneuvering room, but there is only one safe place to lose that altitude – on the prescribed instrument approach courses. If a procedure turn isnt depicted on the approach plate, then it isnt authorized.

In flat terrain, its possible to design instrument approaches in which the altitude losses are gentle, resulting in a nice, stable descent profile. As youve probably learned, unstable descents usually lead to problems with aircraft control and diverted attention. In mountainous terrain, the descent profiles tend to be steep. Many of these approaches require being fully configured, gear down, and on the final approach speed before you reach the final approach fix. Otherwise, the steep descent from the final approach fix will cause the aircraft to gain speed and you wont be able to slow down.

Stable approaches are a real must whether in flat land or the mountains, but the stakes are, ahem, higher in the mountains. If you hit the final approach fix and youre not slow and dirty, you will find it very difficult, if not impossible, to get the aircraft stabilized during the final approach. Many air carrier pilots who have flown these approaches repeatedly will have the aircraft slowed down before intercepting the intermediate segments of the approaches. They know its impossible to get the aircraft slowed down and descending if they are behind.

If you can try these approaches in VFR conditions, you will discover these problems and be prepared when you are faced with doing the approach in IMC or night conditions.

The steep descents, of course, are due to the sharply rising terrain that nears the approach courses. About one and half miles north of the runway into Jackson, there is a large hill immediately to the east of the final approach course that is very, very close. I have friends who own a ranch there and weve often observed aircraft slip out of the bottom of the clouds perilously close to the butte. Lets just say that the tread on the bottom of their landing gear is almost readable.

The criteria for instrument procedures includes specific distances from obstacles in order to ensure adequate separation. The instrument approach designers go to great measures to keep obstacles as far apart as possible, and then the FAA flight checks the approaches as a form of quality control. As long as you are on a segment of the approach, you are guaranteed separation.

Neatness Counts
Unfortunately, precision approach guidance to the runway threshold is almost non-existent at these airports. To make matters worse, these hills are usually unmarked and unlit.

Complicating matters is the fact that the missed approach points are generally quite far from the runway because of the terrain. This creates several additional risks.

Its well known that the descent from the MDA to the runway is very prone to human errors. Unlike precision approaches, which provide glide path guidance nearly to the runway threshold, a non-precision approach demands the pilot determine the proper time to leave the MDA for a stabilized approach to the touchdown zone.

In flat terrain, during daylight conditions, with a good horizon, thats a fairly benign procedure. However, its anything but easy in these mountain airports. For starters, the missed approach point is often located far from the runway at a very high altitude above the runway in order to provide sufficient room for the aircraft to perform a missed approach. It simply isnt possible to have lower approach minimums into most of these airports because an aircraft would be unable to climb out if it proceeded too deep into the valleys and canyons.

Hence, the transition from MDA to the runway threshold is longer and gives the pilot more chances to meet some of the pitfalls.

Once you have descended from the MDA on the visual transition to the runway, you must depend on your eyes to keep you away from obstacles. A lot can happen during those excruciating minutes proceeding from the MDA to the runway.

If you lose sight of the runway during the visual transition to landing, you are essentially flying blind and should execute a missed approach if youre flying in flat terrain. However, in Aspen, Jackson, Sun Valley, Missoula and most of the other Rocky Mountain locations, you are deep down in a canyon or valley. The missed approach point is behind you – and also several thousand feet higher. If you turn to get back to the missed approach point in an attempt to get reestablished on the missed approach procedure, you will probably hit terrain. It is a Catch 22.

Once you descend from the MDA and are past the missed approach point, you are given no protection from obstacles and no assurances that your climb and turn rate will be able to get you out of that hole. This is a very insidious and dangerous trap.

The missed approach procedures at these locations are very steep. Commercial operators are required to meet the climb gradients on the missed approach with one engine inoperative. This very restrictive condition requires operators to download their aircraft to ensure they can meet the climb gradient.

Remember these airports are very high, at 7,000 feet msl or higher, and the missed approach procedures sometimes dont terminate until they join a holding pattern clear of the terrain at 15,000 feet or higher. Aircraft performance at such density altitudes can be anemic at best – particularly in a piston airplane without turbocharging – and when you are trying to make those steep climb gradients, having anemic climb rates is scary.

Your Lyin Eyes
The airport environment plays a big role in the difficulties of these approaches. One of the important cues in flying the final leg of a visual approach involves observing the angles of the runway with respect to the horizon. That works fine in flat country, but there is no natural horizon when performing an approach into mountain airports. This greatly complicates your ability to fly a smooth, stable final approach path.

Approach light systems can aid the pilot with glide path control, but those are effective only when you can see the lights. The VASI is quite informative for glide path control, however it is guaranteed to provide obstacle clearance only when the aircraft is within 10 degrees of the centerline and within 4 miles of the runway. Thats not much.

The approaches into many mountain locations require rather large turns and descents, and the runways are obstructed by terrain until the pilot gets quite close. In other words, approach light systems are of rather limited value.

Other visual illusions are created by the narrow canyons. Roads run through the canyons and adjacent to the runways. When breaking out on the approach in marginal visibility, car lights can be distracting, tricking you into believing that the runway is located in a different location, or else creating the illusion that the runway is moving.

The roads are usually surrounded by no other lights. There seems to be a really magnetic power to the lights that are visible. Sun Valley and Aspen are examples of airports with roads adjacent to the approach paths of the runways. Ketchikan, on the other hand, has a seaway adjacent to the runway, so dont be surprised when you break out on the approach and find boats immediately adjacent to the approach path.

One-Way Road
Sun Valley and Aspen are good examples of one way in, same route out approaches. The approach into Sun Valley enters from over the Snake River Valley and flies along the valley created by the Wood River. The airport is located several miles up the narrow valley.

The MDA on the approach is several thousand feet above the runway and the missed approach point is near the foothills, unable to be closer to the airport because of the rapidly rising terrain. The missed approach is an immediate turn back toward the lower terrain.

Assuming that you could see the runway from the MDA and proceeded to the airport, a go-around or circle to land would be a very risky maneuver. Ive circled in VFR conditions and it requires flying around some intervening terrain along the steep canyon walls. The intervening terrain will hide the airport from your view until you turn onto base leg and proceed back over the river canyon.

Flying straight ahead on a go-around is not an option at many of these locations. At Aspen and Sun Valley, going straight ahead takes the pilot into a rapidly rising bowl surrounded by high peaks. The canyon walls steeply outclimb the aircraft. They are basically situated in box canyons, with precious little room for maneuvering in daytime VFR conditions. I shudder to think of attempting it in IMC.

Weather or Not
Mountain weather is a very complicated phenomenon because the mountains create their own micro-climates. The weather can vary significantly in just a matter of minutes. Its nothing for the visibility to be completely obscured by blizzard-like snow and completely clear just minutes later. The weather can vary substantially from one side of a ridge to another, ranging from blizzard-like conditions to sunny conditions within fractions of a mile.

Problematic localized weather conditions in mountainous areas contribute to an annual average of 17 aviation fatalities in the Colorado mountains. Officials have recently installed Automated Weather Observing Systems at two ski resorts and four mountain passes. These should provide pilots with more reliable information about potentially dangerous localized weather conditions.

The AWOS remotely monitors, then reports temperature, dew point, wind speed and direction, altimeter settings, visibility, cloud height and sky coverage, precipitation and thunderstorm activity directly to air traffic controllers and aircrews. However, that is still a very small sampling of the weather activity you could encounter during the descent and approach into one of these locations. Aspen, Jackson, Sun Valley and Missoula are served by control towers during daytime hours, which helps with obtaining a weather report. However, that weather report is for the immediate vicinity of the airport, while the weather around the ridge or farther up or down the valley can be completely different.

Rapidly changing weather conditions are rather common in this terrain. I spoke with one of the EMS crews that immediately responded to the scene of the Gulfstream crash and learned rescuers were unable to drive faster than 20 mph because of the white-out snow conditions.

The long and winding visual transitions from the visual descent points to the runway are particularly troublesome during rapidly changing weather, which is very common during the infamous springtime storms that plague the Rockies. The visibility can change within a minute, going from VFR to white-out conditions. You may be at the visual descent point with the airport in sight, determine you have satisfactory visibility to make the visual descent, and commence the long visual descent to the runway, only to have the visibility suddenly go to zero.

There you are, past the missed approach point, down in a canyon, with few options and no protection.

The terrain has tremendous effects on the wind patterns. Wind patterns in the rugged terrain are not as simple as some books show. The canyons create funnels that accelerate the airflows. Ridgetop winds can proceed downward, causing vortices that create turbulence and constant up and down drafts. When ridgetop winds are relatively mild in the summer months, daytime winds will tend to flow up canyon, which means tailwind conditions when landing at many of these airports.

Why not land into the wind? Some of these locations are boxed in by the canyon walls so tightly that circling is not advised. Flying a stabilized approach in turbulent winds is tough enough, but tailwinds on landing are an added challenge. Dont be surprised if the winds completely change from a headwind to a tailwind several times throughout the final segment of the approach.

Its hard enough to fly a stabilized approach in VFR conditions when the winds are squirrelly, and it gets much more difficult during MVFR or IFR conditions.

When the winds are calm and the thermals are quiet, flying in the smooth air around the mountains is gorgeous. But smooth air is rare.

If you plan to fly into mountain airports, dont try the approaches in IFR or night conditions without first flying the approach in daytime VFR conditions several times. The practice delivers many advantages when youre doing it for real.

It allows you to form an accurate mental picture of the proximity of the terrain to the courses. If your instruments arent tight enough for the approach, it is better to discover this in daytime VMC when you can see the rocks, rather than in IMC or at night.

You can see the effects of shooting through a course and how soon corrective action must be taken. You will be exposed to the turns and descents of the approach.

Perhaps you will make a mistake in VFR conditions, setting in the wrong radial or frequency, or not descending at a sufficient rate. These will be easy to spot in VMC, and will help prepare you for the day when you have to shoot the approach for real.

Also With This Article
Click here to view “For VFR Pilots, the Going Gets Easier.”
Click here to view “Mountain Approaches in the Real World.”

-by Pat Veillette

Pat Veillette is a Utah-based Part 121 pilot. He has flown the mountains extensively on medical missions and delivering smoke jumpers.


Please enter your comment!
Please enter your name here