One clear, smooth night about 35 years ago, I was flying a load of passengers over Virginias Blue Ridge Mountains enroute from Dayton, Ohio, Washington, D.C. Suddenly, the Convair started losing altitude – big time. The airspeed dropped 60 knots in what seemed like just a couple of seconds.
I jammed the throttles as far forward as I could get them, heard the throaty roar of the two Pratt & Whitney engines as they ramped up to full power – but absolutely nothing happened.
I didnt know it at the time, but the combination of winds and jagged terrain below were teaching me my first lesson about mountain flying.
Just as suddenly as it began, the airplane stopped descending and righted itself, and we restored normal cruise flight. We had flown out of whatever it was. I was clueless.
You dont have to live and fly in the shadow of 14,110-foot Pikes Peak to understand that flying is a little different in the mountains. Theres a lot to learn about mountain flying, starting with the fact that they dont have to be all that high to be dangerous.
The NTSB accident database is littered with stories of people who flew in the mountains with little or no forethought, mountain-flying savvy or preparation of any kind – and those who knew better but just didnt follow what they knew. Accident reports are their stories.
Healthy caution, good planning and informed judgment can eliminate undue hazards and open the door to the wonderful world of mountain flying.
Carelessness or deliberate disregard for the rules causes some accidents, but most of them happen to people who are totally clueless of the hazards. First and foremost, the airplane, engines, pilot and propeller are all much less efficient at higher altitudes, and that makes them much more vulnerable.
Couple the inefficiencies with rugged, inhospitable terrain affording few good landing spots, strong updrafts and downdrafts, mountain waves and ridge turbulence of various intensities, difficult-to-predict local weather conditions, strong horizontal winds, spotty weather reporting stations, relatively infrequent PIREPs and other factors – and its clear that there is troubles brewing for the unprepared.
When the Real Winds Blow
Everyone knows that the potential for squirrelly air currents exists when wind flow is disrupted by some obstruction, such as a building, slope or mountainside. But if you elevate the wind and obstructions to very high density altitudes, such as those that exist at mountain elevations on all but the coldest days, it is routine to experience natural forces more powerful than a light airplane can handle.
Even when it isnt windy, density altitude is a sinister factor where airplanes are concerned. The important point to remember is that both altitude and winds are significant considerations when flying near mountains.
Two major factors in mountain flying are the engine and the pilot. Some forethought and planning are necessary to counteract adverse effects on both.
Mountains can produce forces more powerful than you or your airplane have the ability to counteract. In some situations, the terrain rises faster than the airplane can, even at max power. You have just run out of options.
Reduced atmospheric density takes its toll on engine power. As the hours pile up on the engine, power output naturally suffers. Valves loosen, rings wear, compression decreases, softer engine parts and fittings degrade or become restricted, tolerances increase and air filters become dirty.
For example, take a typical 200-hp engine. An engine might lose 15 percent of its power due only to aging. That leaves a 170 hp machine. Then, as density altitude increases, your engine power further declines by about 3 percent per 1,000 feet of altitude. At a density altitude of 12,000 feet, the net effect is that your normally aspirated 200 horsepower engine develops only a little more power than a Cessna 152 does at sea level.
To complicate matters, the propeller and the wing are also less efficient in the thin air.
Just how severe can it get? A hotter than standard day at the Leadville, Colo., airport, for instance, occurs anytime the temperature rises above 23 F. When its a pleasantly cool 60 F day at the Leadville airport, elevation 9,927, the takeoff distance increases by at least 300 percent compared to a sea level departure – and that assumes perfect piloting technique and performance specified for a new airplane in the POH.
At Leadvilles altitude, your rate of climb is reduced by more than 80 percent. That means that 500 fpm is reduced to less than 100 fpm at pattern altitude. If youre trying to vault over a mountain pass, forget it. There just isnt enough performance left.
Aspen, Colo., another popular mountain resort, is at just under 8,000 feet. But thats not the major consideration at Aspen or the many other fabulous resorts dotting Colorados mountain landscape.
The problem in Aspens specific case is that nearby Independence Pass has a road elevation of more than 12,000 feet. Although not on a recommended mountain route, the pass is a tempting shortcut.
When the temperature is only 50 F at Independence Pass, the density altitude there is in excess of 14,000 feet. The specific effect of that is difficult to compute because the values are well off of the density altitude chart, as is the capability of the engine, the propeller, the wings and the pilot.
An altitude of 14,000 feet is too high for even a lightly loaded 200-horsepower airplane to safely fly in most cases. Combine an old engine, a 55 percent reduction in engine horsepower, a propeller and wing with lowered efficiency, a pilot who ought to be on oxygen, and youve got the ingredients for trouble.
Regardless of how beautiful it may look below, there arent a lot of places to land if your routing hasnt been carefully planned. Throw into the equation fast-changing weather conditions (characteristic of the mountains), venturi-effect winds flowing through the high passes, up- and down-drafts naturally occurring in valleys, and there are more than a few things to think about.
Education on the dynamics of mountain flying is the first step, and there is a lot out there. The FAA, for instance, has just completed a new package on mountain flying.
The effects of altitude on the pilot is an important consideration. Most pilots have heard stories from veterans of altitude chambers on how crippling the lack of oxygen is. Many, however, incorrectly presume that hypoxia cant set in until the middle teens or higher. After all, they reason, FAR 91.211 prescribes when oxygen is required.
Some people, however, can suffer from what has recently been termed altitude sickness merely visiting lower mountain elevations, nevermind trying to fly an airplane at 10,000 to 12,000 feet. Depending on the individual, motor skills can slow and judgment become impaired at even nominal altitudes.
The only way to tell for sure is to invest in a pulse oximeter to measure blood saturation. An excellent one for cockpit use is the tiny Nonin Onyx, which is the size of a couple of nine-volt batteries and costs less than $400. In addition to warning of hypoxia, it can help those with supplemental oxygen get the most out of their tanks by telling them exactly how much oxygen is needed.
In addition, follow these 10 commandments of mountain flying:
• Turbulence is proportional to winds. Dont fly when mountaintop winds exceed 30 knots.
• Approach ridge lines at 45 degrees, not 90 degrees. After crossing, depart them at 90 degrees. If you run into trouble approaching the ridge, bail out with a 90-degree turn toward lower ground.
• Cross mountain passes and ridge lines at least 1,000 feet agl. If necessary, climb to crossing altitude at least three miles before the higher terrain.
• Be wary of surface observations. They are usually for valley locations and winds at higher altitudes can be significantly different. Check 9,000 feet and 12,000 feet winds as well.
• Use POH performance charts to check the climb capability of your airplane at the altitudes and weights you will use. Do it on the ground before you fly and modify the book numbers with your own knowledge of the airplanes real-world performance. Once airborne, verify that the airplane will, in fact, climb as expected. Dont exceed 90 percent of the max gross weight during mountain operations.
• Check out go-around capability at your destination and alternates in the same manner, based on predicted weights and temperature forecasts.
• Get a good weather forecast, emphasizing the flow of the wind; check pressure differentials to determine drainage airflow (from higher to lower pressure).
• File and activate a flight plan specifying the actual route you intend to fly. Have at least one alternate – maybe more.
• Monitor radios (where possible), check Flight Watch and provide PIREPS as your flight progresses.
• Come to the High Country early and take the long-standing advice to get a good mountain checkout from a knowledgeable CFI before you venture out on your own.
Getting and Using Weather
Always get a good briefing from someone familiar with the specific weather area in which you intend to fly.
Mountain weather reporting stations are few and far between. When you are briefed, get ceiling reports for mountain passes, check temperature/dewpoint spreads and get icing levels and reports, if these are available. Dont assume that the latest report is accurate for current conditions. Hedge against uncertainty by having an alternate plan.
Remember that weather is caused by differentials in temperature and pressure. Look for them. Air is accelerated and lifted as it strikes mountains, creating clouds, fog, turbulence (even mountain waves) and other hazards. Look for lenticular clouds, rotor clouds and other telltale signs of trouble.
But just because you dont see trouble doesnt mean its not there. Extreme density altitude and high winds are seldom visible. If you cant recognize telltale cloud formations, check out a good weather book and research them before you fly.
Using Lower Terrain
State aeronautical charts usually indicate preferred routes. Use them.
In addition to those routes, Colorados chart includes commonly used frequencies, a density altitude chart, a wind component chart, the Koch Chart, specific information on navigable mountain passes, and special considerations for each phase of flight.
Plan your route via valleys and lower terrain, but dont fly in the center of the valleys. Know which way the wind is blowing and fly on the updraft sides of the valleys. Downdrafts on the wrong side could be more powerful than your airplanes maximum rate of climb.
Prepare navigation logs with valley magnetic courses and compute magnetic headings. Navigate point-to-point by DR and pilotage. Back that up with loran, GPS, VORs or whatever other aids might be available.
Mountain Emergency Procedures
When you fly, dress as though you had to survive on the ground and make sure you have an emergency kit with you. If you develop an engine problem, icing or hit a downdraft you cant out-climb, turn away from high terrain and try to go to lower elevations where there are higher temperatures and less wind.
If you dont know anything about survival and have never taken a course in the out of doors, study up.
Mountain flying is fascinating and beautiful, but only if youre prepared. You will encounter higher terrain than that to which you are accustomed. Unseen hazards are present.
You must overcome both ignorance and a built-in sea-level mind-set. Expect degraded performance and rapidly changing weather. Be prepared at times to just sit it out.
Get a checkout with a knowledgeable instructor before you go. Above all, be confident that you know what youre doing.
Also With This Article
Click here to view “Even a Molehill Can be a Mountain of Trouble.”
-by Wally Miller
Wally Miller is a CFII and Gold Seal CFI with more than 7,000 hours.