Flying in mountainous terrain presents a number of challenges that need to be fully understood before you start flying to high altitude airports in mountainous regions. If like most pilots your primary training occurs in the lowlands you will need to get some additional training from an instructor who is familiar with mountain flying before head for the hills.
The main items to consider before flying in the mountains are the following:
- Airplane selection.
- Route selection.
- Altitude selection.
- Emergency equipment.
- Aircraft loading.
- Weather considerations and personal minimums for the mountains.
- High altitude (Density Altitude) pre-takeoff procedures.
- High altitude (Density Altitude) take offs and landings.
Many trainers are not compatible with mountain flying. Many pilots will not contemplate flight into the mountains with less than 160 hp. However you need to consider your own airplane’s performance and equipment and the specific characteristics of the place you intend to fly. You are significantly increasing your risk exposure anytime you venture into the mountains with anything less than two turbine engines and a pressurized cabin so it’s very much a case of what level of risk you can tolerate. Less engines and less power mean more risk. If you think this sounds like I’m discouraging you from venturing into the mountains in your single engine trainer you are correct. Most single engine trainers are only marginally acceptable for mountain flying and need to be operated in the mountains very cautiously and only in optimum weather conditions.
Remember the heavier load you ask you airplane to carry the worse it will perform in the mountains. Just because an airplane is within the weight and balance envelope does not mean it will have adequate climb performance in the mountains. For the purposes of mountain flying many four seat airplanes need to used as if they only had two seats in order to retain sufficient climb performance. Look for an airplane that will be able to maintain a climb of at least 500 fpm at the maximum altitude at which you intend to fly at the weight at which you intend to fly. The weight should be well within the normal operating range of the airplane.
When considered from the perspective of a private pilot flying a normally aspirated piston engine single route selection should be based on minimizing the time spent and distance covered in the vicinity of mountains where the terrain is sufficiently steep that it would be difficult to land in the event of an emergency. It is also necessary to plan a route that can be flown at altitudes that are compatible with the performance and equipment of your airplane. Prolonged flight above 10,000 MSL during the day and 8,000 MSL at night is not recommended without supplemental oxygen and for normally aspirated single engine airplanes climb performance deteriorates significantly with altitude. There are many good reasons to limit your exposure to difficult terrain. It’s often appropriate to select a more circuitous route in order to avoid mountains.
If your destination is in the mountains or if it is not practical to fly around the mountains you will need to decide on the best way to get through the mountains to your destination. For those of us flying small singles we often really do fly “through” rather than “over” mountains. For us the luxury of a high altitude direct route over the mountains is usually not an option. The high altitude direct approach may be ok for those with more than one engine and pressurized cabins but for us this technique is usually beyond the performance capability of our airplanes. Although a straight line works well if you are several thousand feet above the terrain it’s a less attractive proposition if you cannot operate that high due to lack of performance or oxygen. Instead of a high altitude direct route consider a route keeps you away from the highest and most rugged terrain. Following valleys my allow you to fly lower and to keep in the vicinity emergency landing areas that are not too remote. When planning your route consider where you would land in an emergency and if you land is it someplace where you can survive on the ground or where rescuers can reach you. Avoid routes that put you in remote wilderness regions. It’s ok to fly down a valley with mountainous terrain above you on either side as long as the valley is sufficiently wide that you can reverse course if you encounter conditions you don’t like. You will have more space in which to reverse course is you fly along one side of the valley rather than down the middle.
If you are approaching steep terrain plan your route so you do not approach the high terrain at a 90 degree angle. It’s better to cross at a 45 degree angle so that in the event you encounter a downdraft or turbulence it will be easier and quicker to turn away towards lower ground.
Consider the direction of the wind when planning your route and think of the air flowing over the mountains like water flowing down a rocky stream. The faster the airflow (winds aloft) and the rougher the terrain the more likely it is you will encounter turbulence and down drafts. Turbulence and downdrafts are more likely to occur on the leeward side of the mountains. If possible plan to fly on the windward side of mountainous terrain.
If your destination is in the mountains talk to someone based at your destination who can recommend a route. There are often local conditions and procedures that you will not be able to figure out from just looking at a chart. Talk to a CFI based at your destination or ask the local FBO or flight service station if they can refer you to a local accident prevention counselor who can provide you with information on preferred local procedures.
In a perfect world where we all flew airplanes with at least two turbine engines and pressurized cabins we would take the altitude of the highest peak and add 50% to select a minimum altitude at which to cross mountains. In the real world of normally aspirated singles, lack of oxygen, climb performance and the effects of the winds aloft on our groundspeed at these higher altitudes mean we usually have to settle for something much lower. In fact it’s often a case of following open valleys along highways, rivers or railroads at altitudes that are sometimes less the surrounding terrain. As always you need sufficient altitude to avoid obstructions and that if a power unit fails your can land without undue hazard to persons or property on the surface and preferably enough altitude that you can glide to a place where you stand a chance of surviving a forced landing.
A possible altitude selection strategy is to chose an altitude at which your airplane should still be able to climb at 500 fpm, that puts you at least 2000 feet above the terrain directly below the airplane (its ok if there is higher terrain on either side as long as there is space to reverse course), and at which you can satisfy the requirements for oxygen. However for every flight into the mountains you need to consider the specific circumstances for that particular flight to determine the most appropriate altitude taking into account all the variables including factors such as terrain, aircraft performance, winds aloft etc.
When planning a flight in the mountains consider what it’s going to be like on the surface in the region you are crossing. If you had to make an unexpected landing do you have the clothing and supplies necessary to survive on the mountain? There are many tragic stories that can be recounted by rescue services of pilots who survived forced landings in the mountains only to perish before they were found due to exposure to the elements in the absence of adequate clothing or supplies. Carry the food, water, clothing and equipment you need to live outside the airplane if you unexpectedly find yourself on the ground. This is a good strategy for any flight but it becomes more critical in the mountains or other wilderness areas.
One of the main causes of accidents at high altitude airports is pilots from the lowlands attempting to take off in excessively loaded airplanes. The typical scenario is the airplane full of people and baggage gets into ground effect but fails to get more than a wingspan’s altitude above the runway. The airplane then collides with terrain off the end of the runway or stalls and spins if the pilot tries to force it to climb with ever increasing back pressure on the control wheel. In the mountains it’s not just enough to be within normal weight and balance requirements. The airplane must be light enough and have enough power that it has sufficient excess thrust to climb adequately. Higher altitude and higher temperatures dramatically reduce performance so keep loads light in the mountains.
Excess weight increases the distances needed for take off and landing. It also reduces rate and angle of climb, range, cruise speed and service ceiling whilst increasing stall speed. For all these reasons be very careful that your airplane remains well within normal weight and balance limits.
Many four place airplanes should be operated in the mountains as two seat airplanes in order to maintain sufficient climb performance.
Do not compromise on weather minimums in the mountains. For private pilots flying normally aspirated single engine airplanes this generally means good day time VFR weather. Weather conditions can change quickly in the mountains so check forecasts carefully and get an update on current conditions before you venture into the high terrain. In addition to needing stable air, high ceilings and good visibility you need to carefully consider temperature and winds aloft.
When temperatures go up the density of the air decreases. The engine develops less power and the aerodynamic performance of the propeller also deteriorates. This reduced thrust in the less dense air increases take off distances and decreases climb performance. If the temperature is high enough there may come a point where the airplane will be unable to take off at high altitudes. Take a look at the take off distance tables for your airplane and you will see distances increase significantly at high temperatures and in some cases reach a point were takeoff can no longer occur. Takeoff performance tables usually work on the basis of considering Density Altitude. Density Altitude is a measure of air density that is determined by correcting Pressure Altitude for temperature. The higher the temperature the higher the Density Altitude and the worse the performance of your airplane. Plan your flight to avoid high temperatures.
Winds aloft have a dramatic effect on the airflow in the vicinity of mountains. The faster the airflows over mountains or rough terrain the greater the chances of encountering strong downdrafts or turbulence. Strong winds aloft can result in mountain waves with downdrafts that can easily exceed the climb performance of your airplane. If ridge level winds aloft are 30 knots or more do not venture into the mountains. Winds aloft over 20 knots are cause for concern but 30 knots or more should result in a definite no go decision. Remember that actual wind velocity over mountain passes may be significantly higher than where winds are forecast or reported. Be sure to check your groundspeed as you approach the mountains. Monitor your groundspeed to determine if winds aloft are as expected and check in with Flight Watch for pilot reports and updated weather before you cross the high terrain.
If you encounter turbulence adjust power and trim to maintain maneuvering speed and fly away from the turbulent area. As always your number one priority is to fly the airplane so don’t panic or try to fight every bump. You’ll appreciate your seatbelt being securely fastened before you encounter turbulence.
If you encounter a severe downdraft use full power and maintain best rate of climb speed (Vy) for the altitude at which you are operating. Do not allow the airplane to get too slow and risk stalling. Fly towards lower terrain or an area of updraft or smoother air.
High altitude (Density Altitude) pre-takeoff procedures
As always you need to perform a thorough pre flight inspection. Never attempt to takeoff with any frost, ice or snow on your windshield, wings or control surfaces.
The importance of correctly calculating take off distance increases with altitude. Make sure you take into account altitude and temperature and all other factors noted on the performance tables for your airplane when calculating take off performance. In order to stand a chance of getting the performance stated on the tables you must comply with all the conditions specified on the tables. This includes correctly setting the mixture for the altitude at which you will be taking off. This usually means adding a step to your normal pre take off checks where you perform a full power run up and lean the mixture for maximum power prior to take off. Most airplanes will perform very badly if you try to take off with the mixture full rich at high altitude. Be sure to follow the procedure specified in your airplane’s flight manual to set the mixture prior to taking off at high altitude.
High altitude (Density Altitude) take offs and landings.
Before you take off or land in the mountains make sure you have carefully calculated takeoff or landing distances and determined runway length available. You can only hope for the airplane to perform as predicted in the performance tables if you follow the procedures specified in the manual. Even then you are unlikely to do as well as the test pilot flying the brand new airplane on which the tables were based. Take into account runway length, slope and surface condition as well as wind and Density Altitude. Look beyond the runway for obstructions in the path of your approach or climb out and make sure you will have enough climb performance to clear any obstructions or rising terrain.
Follow the procedures stated in your airplanes flight manual regarding use of flaps and recommended airspeed. When you take the runway and add full power check all engine gauges are in the green and that you are developing the expected rpm. Rotate to the pitch attitude at which the airplane will lift off at the recommended speed and then pitch for the recommended climb speed. If there are obstructions to clear you will probably be using the best angle of climb speed until obstacles are cleared (Vx). If there are no obstacles to clear you will probably be using the best rate of climb speed (Vy) specified for the altitude. As altitude increases the best angle of climb and best rate of climb speeds converge. Be sure to establish the required speed for the Density Altitude at which you will be flying. Because of the less dense air at high altitude you will use more runway to reach rotation speed and your groundspeed will be faster when you reach rotation speed than when working with the same indicated airspeed at sea level. To get the same indicated airspeed in less dense air you need to move the airplane through the air mass faster to force more of that less dense air down the pitot tube to get a particular indicated airspeed. On climb out be aware that the terrain may create a false horizon effect whereby you mistake mountain peaks for the horizon resulting in excessively nose high attitudes. Remember that the horizon is generally nearer the base of mountains and reference your airspeed indicator to maintain the correct airspeed.
Landing at altitude requires careful control inputs. Fly the indicated airspeeds specified in your airplanes flight manual but be aware that for a particular indicated airspeed your groundspeed will be higher at altitude. This will mean you use more runway and that at any given indicated airspeed the airplane will be moving at a faster groundspeed. It’s important you reference your airspeed indicator to ensure correct approach speeds are maintained and that you do not allow the airplane to get too slow. Because you will be touching down at higher groundspeed it’s more important than ever to ensure that the airplane is longitudinally aligned with the runway and that any drift has been eliminated prior to touchdown. Beware of crosswinds in the mountains and be prepared to Go Around if your approach is not working out as planned.
Higher attitudes mean less dense air which makes it harder for pilots and engines to get the amount of oxygen they need to function normally. Less oxygen results in deteriorating aircraft and pilot performance. Pilots start to suffer before engines and sometimes your airplane will have a turbo charger enabling your airplane to climb to altitudes that will really get the pilot in trouble unless a supplemental oxygen supply for the pilot is available. Prolonged flight above 10,000 MSL during the day and 8,000 MSL at night is not recommended without supplemental oxygen. However tolerance to altitude is hard to predict and varies depending on the altitude at which you spend most of your time.
The FAR’s state that no person may operate a civil aircraft of US registry at cabin Pressure Altitudes above 12,500 feet MSL up to and including 14,000 feet MSL unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration. At cabin Pressure Altitudes above 14,000 feet MSL the required minimum flight crew must be provided with and use oxygen for the entire flight time at those altitudes. At cabin Pressure Altitudes above 15,000 feet MSL each occupant of the aircraft must be provided with supplemental oxygen. Additional rules apply to aircraft with pressurized cabins.
Failure to comply with these rules can result in some very undesirable physiological effects caused by hypoxia that can greatly impair your ability to fly the airplane. Hypoxia is a state of oxygen deficiency in the body and can result in impaired judgment, memory, alertness and coordination and eventually loss of consciousness. Symptoms which can be hard to recognize include headache, drowsiness, dizziness and a sense of euphoria or belligerence. At higher altitudes peripheral vision may gray out and fingernails and lips may develop a blue coloration prior to loss of consciousness. If symptoms of hypoxia are detected immediately use supplemental oxygen and/or descend as much as terrain will permit.
The mountains are definitely a place where you should plan on using superior judgment to avoid the need for using superior skill. Pilots like mountaineers need to plan thoroughly and have good equipment plus the will power to make a no go decision or to turn back if conditions are not ideal. A lack of planning, inadequate equipment or bad judgment will definitely get you in trouble in the mountains.