Mountain flying

Operations from, into, and around airports in mountainous terrain require special attention and even specialized training.

By Karsten Shein
Comm-Inst
Climate Scientist

Neither pilot liked this mountain airport. It had a short runway which was often contaminated with snow and ice. And, given the wind, the only viable approach path took them just above a ridge surrounded closely by jagged peaks. That day would be even more challenging because of a strong crosswind, but the company’s CEO was bringing several important clients for a weekend of skiing at the resort near the airport.

However, as the bizjet crested the ridge, a sudden updraft slammed into them, ballooning them almost 300 ft above the glideslope. The pilots reduced power to bleed altitude, but, given the short distance to the runway, they knew they would land long. The gusty winds conspired to keep them aloft further down the runway than they wanted, and, as the mains finally touched, both pilots agreed to slow the airplane rather than go around and fly that approach again.

Unfortunately, they had miscalculated, and no amount of brake action and thrust reversers could keep the jet from plowing into the snow at the end of the runway. No one was badly injured, but the aircraft was damaged substantially.

Every year, millions of flights traverse mountainous terrain and corporate pilots make thousands of takeoffs and landings from mountain airports. Unfortunately, several are involved in aircraft accidents in which adverse mountain weather is a contributing factor.

Mountain flying carries a unique set of weather risks, often compounded by short and narrow runways and approaches that force pilots to thread the proverbial needle through steep valleys and unforgiving terrain. Airports such as INN (Innsbruck, Austria), SMV (Engadin, Samedan, Switzerland), or ASE (Aspen CO) – all popular destinations for skiing – offer good examples of very challenging mountain approaches that are highly dependent on the cooperation of the weather. Some approaches even require specialized pilot training to receive clearance.

Winds

Unlike wind around airports on relatively flat terrain, wind in the mountains often blows through steep valleys and across sharp ridges, altering its trajectory, adding to its speed, and generating severe to extreme turbulence.

At some mountain airports, the wind can be blowing simultaneously out of 2 very different directions at either end of the runway. At other times, the wind at the surface is calm, while the air may be moving very quickly above the shelter of rising cliffs.

Prior to takeoff or before starting an approach into these airports, it is important to fully understand how the wind behaves as you fly the approach or departure course.

If there are clouds, are they moving much faster or in a different direction than what the airport is reporting? Do some of those clouds just beyond nearby ridges look ragged? Are they lens-shaped lenticulars, or a solid deck with a wavy pattern? Those are solid signs of windshear and turbulence downwind of the ridge crest or mountain peak.

At some valley airports, however, the wind can be very reliable, flowing up the valley during the day, and draining down the valley after sundown. Knowing this gives you preflight knowledge of the likely traffic patterns. It also means that at some airports, where the terrain restricts takeoffs or landings from a certain direction, you can expect a tailwind along the runway.

At other mountain airports, the limited terrain forces a runway orientation perpendicular to prevailing winds. This often means encountering wicked and gusty crosswinds. In either situation, it is critical to be certain of both the winds and the crosswind/tailwind limits of your aircraft.

While some local pilots at airports with difficult winds will rely on an instantaneous wind observation to inform a split-second go/no-go decision, transient pilots are best served by sticking with the reported (2-min average) wind for determining their crosswind or tailwind component. In the case of an incident, reliance on an instantaneous wind observation can be ruled pilot error.

Snow

In most high mountain airports, particularly in the middle latitudes, seasonal or even year-round snow can be a major issue. Beyond high and gusty winds, passing low-pressure systems will drive moisture-rich air aloft, and with below-freezing temperatures due to the elevation and season, this can amount to several feet of snow in a day.

If that snow is accompanied by high winds, blizzard conditions can materialize quickly, eliminating any forward or slant visibility without warning. Flying dirty below the ridgeline in a narrow valley when all visibility disappears is not a situation most pilots want to encounter.

Many mountain airports will have deicing service and snow removal capability, but a lot of the smaller ones won’t. During or after a snow event, be sure to query Common Traffic Advisory Frequency (CTAF) or local ATC about the runway condition. If you get no answer, assume contamination with poor traction or braking action. If possible, a pass over the runway may reveal its condition.

Mountain obscuration

Just as the complex terrain can produce chaotic winds, it also enhances cloud formation as moist air is forced to rise and cool as it encounters rising terrain. At the altitude at which the air becomes saturated, the still rising air will blanket the higher terrain in a fog that can obscure it from view easily. Many controlled flight into terrain (CFIT) accidents have occurred when pilots lose their situational awareness and inadvertently drop below minimum safe altitude (MSA) or deviate from their planned flightpath.

When approaching or departing on a path that requires a high vertical rate or runs between areas of higher terrain, if you are suddenly in instrument meteorological conditions (IMC) and drift even a degree or a few hundred feet per minute, you could collide with the terrain without any warning.

In mountain flying, remain aware of the MSA for each segment and pay close attention to your heading and altitude. On departure or approach, even a precision one, it may be best to find an alternate if your path below nearby terrain is shrouded in cloud as even a small error could bring disaster.

Of course, even if special certification isn’t required, experience is often the best teacher, and many simulators are able to faithfully simulate your aircraft and adverse weather conditions to practice approach or departure from many mountain airports worldwide. Becoming comfortable with those operations in a simulator, or in person with a local instructor or experienced copilot, can reduce the likelihood of pilot error in these situations.

Finally, while most people would consider an airborne view of endless snow-capped peaks as a beautiful experience, pilots should also view them with a sense of concern. If they lost power and had to land, would there be a place they could do so safely? Even if deploying an emergency parachute for a gentle landing, is there civilization nearby? A road, perhaps? What are conditions like at the surface? In addition to knowing the weather at your cruise altitude, it is worth familiarizing yourself with the surface forecast along your route, and making note of any airports and communities, as well as wide valleys.

Even small course corrections to keep you near these places may greatly increase your margin of safety in an emergency. Importantly, a mountain survival kit is advisable whenever flying into or across the mountains.

Just like what motorists may carry for winter driving, such kits often include emergency blankets and fire starters, signaling devices, a multi-tool, and food and water for several days. And given the lack of weather observations in mountainous regions, if you see conditions other pilots should know about, please file a Pirep.

Karsten Shein is cofounder of 2DegreesC.org. He was director of the Midwestern Regional Climate Center at the University of Illinois, and a NOAA and NASA climatologist. Shein holds a comm-inst pilot license.