Essential Techniques for Mountain Flying

Introduction

Mountain flying in FS2002 (and many other sims) offers a whole new set of challenges, as it does to real world pilots. It can be very rewarding, and the default scenery verges on the breathtaking in many areas, especially in the USA.

There are several very important techniques and theories to master to make the most of the mountains, and I have put together this page to help you grasp the basics of flying in this hostile but beautiful terrain. I have researched the information from many real world aviation sources, plus about 65 hours FS2002 high altitude mountain flying experience in Alaska, Montana and Colorado.

The following information specifically relates to normally aspirated single engine piston aircraft, such as the Cessna 172 or 182, operating from fields above 5000', but equally applies to piston twins. Techniques are different for jets or turboprops, and turbocharged piston aircraft have less of a performance hit.

I've assumed that all your simulator realism settings are at maximum, engine set to stop when out of fuel, and your system displays Indicated Airspeed. A good basic knowledge of operating flight simulator aircraft under normal conditions is required, and I have not ventured into techniques for flying in poor weather - that's another story!

Theory

A little bit of theory first. The more you understand how your aircraft works the better you will fly, and I've listed some of the reasons aircraft behave differently when operating from high elevation fields and flying at high altitudes.

Engine Performance

Ask the average driver the power of his car engine and the chances are he won't know. Ask the average pilot and he will instantly tell you the horsepower of the engine (along with a host of other stuff too!). This power output is only true, however, when it is measured at a pressure and temperature standard called International Standard Atmosphere - ISA, at sea level, which is considered to be 1013mb (29.92"Hg) at +15C (59F). Any change from this in temperature, pressure or altitude will affect the engines performance for the good or bad.

Unfortunately for us, high altitude has a negative effect as the thinner air is more difficult to push into the cylinders, quite drastically reducing the power. Your trusty 172 will be at full throttle and feel like it is flying through treacle. By the time you're halfway to the aircraft's service ceiling the power output will be considerably reduced, and many of the fields you'll be flying from will be much higher than this.

Fuel/Air Mixture

There is an ideal ratio of fuel and air mixture (called the stoichiometric mix) which is about 15 parts air to one part fuel, by weight not volume. At about 18:1 there is not enough fuel available and the mixture doesn't burn; at around 8:1 there's not enough air - these limits are known as "lean cut" and "rich cut" respectively. Real engines also use a bit of fuel to assist in cooling the engine, but we won't enter into that here.

Because our air at altitude is less dense, we need to reduce the amount of fuel in the mix, and most simple piston powered aircraft have a mixture control that allows the amount of fuel available to the carburettor to be varied (the throttle control only varies the amount of air). At some extremely high airfields the engine may not even start with the mixture at full rich, so you need to lean it back about an inch (ctrl-shift-F2 several times).

For takeoff you require maximum power, so it's important to set your mixture as best you can before commencing the roll. During the climb you will find your throttle still at max but the power decreasing, and it's time to lean a bit more. Once in the cruise, however, there is a handy gauge called the EGT, or Exhaust Gas Temperature gauge, which will assist you in setting the optimal mixture. To use this, lean (ctrl-shift-F2) the engine gently until this gauge peaks, then enrich (ctrl-shift-F3 two or three times) the mixture very slightly. The engine should be running smoothly and producing about the best power it can.

Remember, if you lean too much the engine will misfire and may even completely lean cut, so be very careful altering the mixture if you are crossing a ridge! Most engines (including FS2002 virtual engines) will usually lean cut on one or two cylinders first, hence the misfire. Don't push your mixture to far either, or your engine will rich cut. As you descend, increase the mixture slightly every 500 feet or so, and immediately if it starts to misfire.

Density Altitude

The higher we go the cooler we expect it to get. Using our ISA atmosphere, the air temperature drops 2C (35.6F) every 1000', so at 10000' we would expect -5C (23F). That's fine up in the air, but if you're 10000' on the ground, surface weather will determine the temperature. In winter this may be -20C (-4F) or less, but in summer we could be looking at +20C (68F) or more. The relationship between pressure altitude (how we normally measure our height in an aircraft), air density and temperature is known as density altitude.

Your aircraft's POH will have a complicated looking graph giving takeoff distances at various altitudes. You could look at your altimeter and work out the distance required, line up nicely and apply full power, only to find yourself running off the other end of the runway! The poor old lycoming doesn't understand your perfectly calibrated altimeter, but only the ambient conditions that it's operating in, and that's the density altitude. To illustrate the difference this makes, at 6000' on a freezing winters day of -20C (-4F), the DA will be about 3100'. On the other hand, at the same airfield on a hot summers day of +20C (68F), the DA will be around 8200', a difference of 5100'!

Density Altitude can often work in our favour, as the example above shows. Some of the very high fields can only be used by piston aircraft in autumn, winter and spring when it's cooler - during summer, operations are all but impossible.

The formula for calculating the DA is quite complicated, but there are plenty free tools available to do it for you. My favourite is the great Virtual E6-B (1.52Mb) flight computer (the whizz wheel), which has a host of other useful functions as well. Remember: always work out your density altitude!

IAS vs. TAS

For our final bit of theory, we need to look at Indicated Airspeed versus True Airspeed. Most ASI's (Airspeed Indicators) measure IAS - Indicated Airspeed, and as your altitude increases your TAS - True Airspeed - will be quit a bit faster. Over 10000' your TAS may be up to 20kts faster due to the less dense air.

When taking off or landing at high fields, your ASI will be reading IAS as usual, but your TAS will be much faster. As the aircraft is still on the ground the TAS will also be the ground speed. Just as aircraft perform relative to density altitude, they do the same with IAS, so although the ground speed will look right for takeoff the aircraft will not rotate. You have to keep accelerating down the runway until the correct rotate speed is shown on the ASI.

To give an example in ISA no-wind conditions, if your aircraft normally rotates at 65kts IAS, at sea level your ground speed will also be 65kts. At Lake Co, Colorado, 9800' up your ground speed will be 75kts when your ASI reads 65kts. You must follow the IAS, and wait until the proper speed is reached.

This also applies to landing, and you will find the threshold appearing much faster than usual, even though your ASI is showing the correct approach speed. After crossing the threshold, bleed the speed off above the runway gradually, and remember your ground speed will be much higher than normal when finally you touch down.

Techniques

As there are distinct stages of each flight, I'll group the techniques to use in that order.

Pre Flight

Good planning is absolutely essential for mountain flying, and many incidents can be avoided by doing this thoroughly. First and foremost, you must check that your aircraft will be able to operate at these extremes. Your aircraft will have a service ceiling that can rarely be exceeded, and remember, this will be the density altitude, not the pressure altitude. When checking or setting your weather, calculate the DA using one of the tools above. If it can't be done, then it can't be done, so there's no point in trying it! If you're lucky enough to get airborne, more than likely you won't be able to cross the first ridge no matter how many 360's you do.

You must ensure that the runway you intend to use is physically long enough. Your takeoff run will be much longer than usual, often much more than twice the distance. Try to obtain real world performance data for your aircraft and use this when planning. Consider also takeoff direction - at some fields there is only one feasible takeoff direction no matter which way the wind is blowing, due to mountains or other major obstacles. Obtain airfield data from the web or other sources to assist you.

Fuel planning is of the utmost importance, as it's unlikely your aircraft will be able to operate at its MAUW. If fuel is available at each strip, then carry enough fuel to get you there with enough reserve to get you back again (remember, you will probably not be flying in a straight line, so take this into account). You'll be surprised at the performance improvement when carrying eight or 10 gallons instead of 20.

If you are using FS_Meteo, or other real-time weather programme, look for alternates, as mountain weather can change very rapidly. As suitable strips can be few and far between up in the mountains, your alternate may be the airfield you started from! And remember, early morning flights in the summer can mean that the field you took off from may be unsuitable for returning to as the density altitude may have shot up.

Starting and Run Up

Most of us have been taught to set the mixture full rich and the prop fully fine for starting, but things may be different up here! Now that you've worked out your DA, if it's much above 5000' you will need to lean a bit before hitting the starter. This is something you'll get the feel for, and as long as the engine starts you can adjust the mixture until the engine is running smoothly.

Your engine will take longer to warm up than usual, so wait for a decent oil temperature before commencing the run up. You will notice a smaller difference in RPM when checking the mags, so take this into account. Even with the mixture set correctly the engine may die after the run up, so keep the RPM higher than normal, and also during the taxi.

Taxi and Line Up

The first thing you will notice is the amount of throttle needed to commence the taxi. This is due mainly to reduced power, but also the prop has less air to bite into. Once rolling, things revert to normal, although you will need a lot more throttle management than usual to avoid either taxiing too fast or the engine cutting out.

Line up as near to the end of the runway as you can, the more you have the better. Set your trim higher than normal, but avoid flap if possible as we are going to need the airspeed, and the loss of lift when they are retracted can be catastrophic. Apply your brakes and conduct a full power check - this will allow you to adjust your mixture to give the best power for takeoff. Don't pull the throttle back to idle after this as the engine will cut out - if you're not ready to go keep it at about 40%. After completing your final checks it's time for the fun to begin!

Takeoff and Climb Out

Slowly advance the throttle while holding the brakes until you feel the prop really biting, then release the brakes and commence the roll. The aircraft will seem to accelerate very slowly at first, and it will be a good few hundred feet before the ASI even registers. Concentrate on keeping the aircraft straight, glancing at the panel every now and then to check your ASI and engine instruments. Forget your ground speed, as it will be much faster than the IAS. Continue accelerating, and don't let the aircraft fly off until the ASI indicates slightly above the normal rotate speed. Pull back gently on the yoke until the aircraft has lifted clear of the runway, but don't try and climb too much too quickly. An initial rate of about 50fpm will allow the speed to build while still over the runway. Ensure you have adequate airspeed before initiating the climb out.

At very high altitudes you may not be able to sustain a rate of climb more than 100fpm without the aircraft becoming dangerously near stalling speed, so you need total concentration. Keep a good look ahead; watch for obstacles; watch your airspeed; ensure your vertical speed is positive; remember as you're near the ground your ground speed will appear high, but it's the IAS you're interested in.

The workload is very high, and the aircraft will feel that's it's wallowing near the stall but the ground will be rushing by! Don't break your concentration for one second at this very critical time. You will need to trim to get the best rate of climb with the safest airspeed to at least 1000' AGL if possible. I find it easiest to trim on the ASI, ensuring that the VSI is reading positive, but not worrying about the exact vertical speed. Don't get distracted - this is no time to enjoy the view!

Climb

Once you have cleared any obstacles and commenced your climb proper, you may want to trim down slightly to let your airspeed build, keeping the rate of climb positive all the time. Forget the throttle, as that will likely be fully open until descent, but lean the mixture slightly every few hundred feet to avoid a rich cut.

Gaining altitude is a painfully slow process, and you must keep an eye on that ASI all the time. It is very, very easy to stall at this time. Your inclination is to pull back on the yoke to gain extra height, but it will be instantly lost in airspeed. Trim for the best you can get, accepting that it will get less as you get higher! Don't let the airspeed drop during the climb - let the vertical speed drop.

You may need to make 360° turns during your climb to clear ridges and mountains. Remember that turning an aircraft will need more power to sustain pitch and airspeed, and you don't have this. Make lazy, gentle turns without too much control input. Your rate of climb should drop slightly, but your airspeed should remain the same. Sudden control surface movements can easily lead to a stall, or worse, a spin, and you may not have the altitude to recover. Even if you do, you have lost all that precious height in the process!

Cruise

This is the nearest you will get to relaxing! Trim your aircraft so that it is straight and level for about five minutes, then adjust the mixture until the EGT gauge peaks. Advance the mixture very slightly to take the needle off the peak and you're set for the cruise. You may need to trim a little after doing this.

In the real world we would have all sorts of nasties such as up draughts, downdraughts, extreme sink, rotors and microbursts to contend with, but these are, unfortunately, not simulated in FS2002. If you have wind set, keep a close eye on drift as it may take you near high ground.

Never head into valleys unless you know there's a way out - you may not be able to turn 180° in the available space. If you must, a good tip is to fly near one side at slightly reduced power. This will give you extra space to turn, a slightly lower airspeed to react, and extra power available to execute quick turn about.

Navigation can be very difficult in this type of terrain, with very few landmarks and features. Make use of your GPS or Navigator, but avoid using the autopilot. Flying by hand keeps you in control of the aircraft all the time. In FS2002 it's very tempting to use spot view, but I recommend staying in the cockpit for the first few hours at least.

Remember, even in the cruise keep a close eye on that airspeed and altitude - the DA may be increasing as the air warms.

Descent

Plan your descent well ahead. If you are off course there may not be a clear path to your FAF which could force you to climb again. Initiate your descent as normal, but be very careful with your airspeed - it's very easy to descend far too quickly and steeply. Keep an eye on your mixture, advancing it slightly every few hundred feet, and don't shut the throttle completely. This will very likely cause the engine to cut out, and may also shock cool it.

Final Approach and Landing

DON'T SET YOUR MIXTURE TO FULL RICH! Set your aircraft up on final much earlier than you would at lower altitudes. The threshold is going to appear quicker with your high ground speed, and it will give you time to adjust your mixture for best power. Fly the approach at the normal IAS; don't be tempted to come in slower as you will not have the power to combat the sink. You will need quite a bit more throttle than normal to keep the correct speed at the normal approach attitude. As you cross the threshold, round out slowly and float in the ground effect. The aircraft will stall before you reach normal ground speed for touchdown, so keep the wheels as near to the surface as possible. The stall horn should be sounding as the main wheels gently touch down, but keep the nose wheel off until the speed reduces to the normal ground speed. Gently brake and you're down! Don't close the throttle completely as your engine will cut - use the taxi tips above to get to the ramp.

Other Considerations

The following information was provided by Steve Armstrong, a real-world Colorado Mountain Pilot, who stumbled across this article. Thanks Steve, for you input.

1) This is not a hard rule, but it is very predictable. Know where the up and down drafts will likely be at all times during your mountain flight. Up drafts are likely to be found on the windward side of a ridge and this is the optimal place to be as the wind/air must rise in order to get over the mountain obstruction. The down drafts and resulting turbulence (which can be very nasty and scary in real life) is found on the leeward side of the ridge as the resulting air which rose over the mountain ridge now cooling and descending into the classic mountain wave.

2) When approaching a ridge in which you wish to cross, approach it at a 45 degree angle so that if you find yourself in a down draft which you can't overcome, a turn of no more that 90 degrees will get you heading downhill. And if you don't hit any nasty down drafts, you can cross the ridge once more and more terrain from the other side of the ridge becomes visible.

3) Fly the ridges and not in the valleys. Not only can you search out the up-drafts by flying the ridges, you can also turn into the valley if trouble arises. If you are flying in the valley and trouble occurs, you may not be able to out climb the rising terrain.


I hope this has been helpful and informative. Many topics discussed above are the same in the real world, but some are specific to our sim. Most of all, enjoy your mountain flights!