According to the National Transportation Safety Board (NTSB), the owner and pilot of the Skyhawk died and her two passengers were seriously injured when the aircraft crashed southwest of Denver at an elevation of 11,548 feet msl. Density altitude at the time of the accident was calculated to be more than 14,000 feet.
The accident report stated that shortly before impact in the "narrow valley" a few miles short of Independence Pass, witnesses observed the aircraft "... flying slow, in a climb, with a nose-high attitude."
This accident and many others involving mountains and high density altitude illustrate a hard truth: Flying in the mountains is a highly specialized brand of flying.
At the Colorado Springs airport (elevation 6,200 feet) density altitude can easily reach 9,000 feet in the summertime. That's no big deal, unless you're thinking about climbing. Some underpowered airplanes just won't do it.
Ask yourself this question. Have you ever flown an airplane that would not do what you wanted it to do? Would it be an eerie feeling to advance the throttle for a go-around ... only to find that the airplane just will not climb? Tapped out - no excess power. None.
Simple awareness and a little bookwork in your motel room the night before would have easily highlighted that, but it's too late to discover this when you need to go around. Would it have even occurred to you that your airplane just might not have enough power for a routine go-around at a high density altitude?
A good mountain checkout will take all the guesswork out of such situations. Without specifically directed thought, study, and dual instruction, many aspects of mountain flying - like limited ability to climb - might never occur to even a "thinking" pilot whose experience was generally limited to flat-land flying.
What makes mountain flying 'different'
There are four things that most pilots take for granted at sea level that are significantly and adversely affected the higher the airplane flies: the wings, the propeller, the pilot, and the engine. The degradation in their effectiveness and efficiency caused by higher effective altitudes is much of what makes mountain flying different.
A considered two-part approach is necessary before you undertake serious flight in the mountains. A certain amount of mental preparation is necessary before you go flying. Then, a good checkout flight will complete the orientation. Both parts are necessary.
The need for preparation isn't limited to the Rocky Mountains or the other "big ones." A 4,000-foot-msl strip in Idaho or 3,200-foot-high airfield in North Carolina, West Virginia, or somewhere else can be just as dangerous - especially when the runway is short, the temperature is hot, and the humidity is high.
Depending on the airplane you're flying, lower elevations can harbor high density altitudes that are just as hazardous as those in the big mountain ranges.
Wings and propellers. Without getting into a technical discussion of aerodynamics, suffice it to say that in the thinner, less-dense air above sea level, wings, propellers, and other airfoils are less effective than they would be in the denser air of lower altitudes. Practically speaking, that's because they have less air to "use." The wings can't efficiently lift as much weight as they can at sea level; the propeller can't accelerate enough air to produce the same amount of thrust.
The pilot. Another component of the equation that can suffer significantly from the reduced density of the atmosphere is the pilot. Pilots acclimated to sea level who find themselves flying at altitudes up to 14,000 feet - where the air density is reduced by half - experience an immediate physiological problem: reduction of the partial pressure of oxygen in the blood stream.
The real problem, however, is that most of us don't even know it because the problem isn't immediately apparent; its effects creep up on the pilot insidiously. Thinking, decision-making, alertness, and a host of other faculties - reactions vary somewhat with each individual - can be markedly impaired with prolonged exposure to even moderate altitudes where GA aircraft typically fly. That's why FAR Part 91 prohibits unpressurized operations above 14,000 feet without supplemental oxygen and limits flight at cabin altitudes between 12,500 and 14,000 feet to a maximum of 30 minutes. The only physiological training for many pilots has been the few paragraphs they've read in preparation for the private or commercial practical test. That superficial understanding of aviation physiology bears more study if you intend to fly in the mountains.
Those who want to tackle the challenge of higher mountains like the Rockies should obtain physiological training from the FAA in Oklahoma City, Oklahoma, or at one of a number of Air Force facilities with altitude chambers. This excellent training is provided at a minimal cost (see 'Going Up,' May 2001 AOPA Flight Training, or read the article online.
Some personal awareness about the potential hazards of flight at higher altitudes is invaluable. A little research into hypoxia, the effects of smoking at night, altitude effects on the body, and other exploration will also help. Ever see that little note in the Aeronautical Information Manual that says vision is degraded at night when flying above 5,000 feet? Check it out - then envision flying near 14,000 feet, which you can legally do without oxygen.
Oxygen deprivation isn't a major factor if you follow the rules. But the documented reduction in pilot efficiency that can result for those who disregard those rules, are unaware of the hazards, or who make no attempt to become acclimated to high altitudes can be added to the list of factors that make mountain flying challenging.
The engine. As an aircraft climbs, the temperature of the air usually decreases at a relatively standard rate (3.6 degrees Fahrenheit or 2 degrees Celsius per 1,000 feet). "Standard day" temperature values at sea level are 59 degrees F/15 degrees C. Atmospheric pressure also declines as altitude is increased, and that pressure reduction causes the density altitude to increase. With the decrease comes reduced engine power. (See figures at right.)
If temperatures fail to decrease with increased altitude as normally expected, "hotter than standard day" conditions will further degrade engine power. Make it your business to know the difference between the density altitude and the pressure altitude where you are operating. That difference can provide valuable tips as to what performance you can expect on a given day.
A normally aspirated engine (one without a turbocharger) routinely loses about 3 percent of its power for every 1,000-foot increase in altitude. That means that a nonturbocharged Piper Arrow that develops 200 horsepower at sea level will generate only about 140 hp at Leadville, Colorado (elevation 9,927 feet msl), assuming that the temperature at Leadville is the "standard" 23.3 degrees F! If that same 200-hp engine is impaired because of high time or poor maintenance and starts out at less than 200 hp at sea level - 10 percent is not an unreasonable reduction for a high-time engine - it will most likely produce less power at Leadville than a Cessna 150 at sea level!
If the temperature happens to be hotter than "standard," the reduction will be even greater. It's easy to see on this basis how a normally adequate general aviation airplane at sea level might not be able to go around, climb, or even maintain altitude in certain situations in the mountains. Winds of only 20 to 30 knots during cruise in the mountains will often develop a degree of turbulence impossible for typical GA aircraft to deal with. Many mountain pilots won't fly after noon or when the winds exceed 20 kt because of the turbulence.
When you add to this limitation uncertain flight planning and irregular terrain, unwary pilots can be accidents waiting to happen. But it needn't be that way at all.
Elements of a good mountain checkout
The key to safe, enjoyable mountain flying is a mountain checkout.
Do your homework. Decide where and when you want to go and what aircraft you're going take. Then get into the nitty gritty. Using the charts provided in your pilot's operating handbook, look at what happens when your airplane operates at the locations you've selected. Get into the specific weather and climatology of the area. Your checkout will give you a good feel for specific circumstances, but try to get some sense of relationships ahead of time.
What are the average temperatures at various times of the day? What are the prevailing winds? How do the ridgelines and other terrain lay out with respect to the prevailing winds? Is turbulence likely? Remember that mountain wave can be encountered more than a hundred miles from the terrain that causes the oscillations.
Get into the performance section of the pilot's operating handbook. Under certain circumstances, you might find takeoff distances that are more than triple what you would compute for the same airplane at sea level, and rates of climb after takeoff that are reduced by 80 percent! Underinflated tires, improperly calibrated airspeed indicators, inaccurately reported runway temperatures, poor pilot technique, improper leaning, runway gradient, and other factors can also affect takeoff performance. Most of the surprises you find will result from the degraded engine power. It just can�t be overemphasized how much performance is lost because of the increased density altitude.
Understand the difference between your operating temperature and the standard temperature for that altitude. Anything above standard temperature will further degrade performance from what you compute.
Look at the climb and cruise performance charts in the pilot's operating handbook. If you're supposed to achieve a certain true airspeed for a given altitude at a given temperature, what do you suppose would be the effect on cruise airspeed if the actual temperature at that altitude were 20 degrees hotter? What effect will the temperature have on your ability to climb?
Check out takeoff and landing performance charts, especially takeoff and landing distances. Increased true airspeeds required to fly your normal indicated approach speeds at higher elevations cause more float in the flare and increase landing distances.
Your 'hands on' checkout
A good checkout will include much more than can be included here: performance; route selection; proper methods of crossing ridge lines; traversing mountain passes; how to get a good weather briefing; and how to determine the effects of specific weather, terrain, and temperature phenomena on takeoffs, landings, and cruise flight.
Don't expect to be flying down in the canyons or "through" the passes, either.
Dead reckoning, increased chart-reading and pilotage, use of the GPS, greater use of alternates, relative unavailability of navaids -all take on increased significance in the mountains, but you'll learn why from a good mountain instructor. You can prepare for your checkout by attending an AOPA Air Safety Foundation seminar on mountain flying. The schedule is on AOPA Online.
Countless books have been written on the subject of mountain flying; most of them are very good. Select a good instructor and get a good "hands on" mountain checkout. That effort will open the door to some of the most rewarding flying you could imagine.
Wally Miller is president of an aviation training, consulting, and marketing firm in Monument, Colorado. He is a Gold Seal CFI who has been instructing for more than 30 years and flying for more than 40.
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