By Amy Hoover. Published in Pilot Getaways Magazine, 1999.

Upon visiting the Idaho backcountry for the first time, pilots will see an airstrip nestled in the trees at the bottom of a deep, possibly narrow canyon and ask, “What must I do differently to make a safe approach into such a constricted area?” The answer lies not in what they must do differently, but in what they can do to make the approach as “normal” as possible.

It is best to fly a standard traffic pattern whenever practical, as it affords a pilot with familiar visual references. You can fly a normal traffic pattern at many of the popular Idaho backcountry airstrips, including Big Creek, Johnson Creek, Moose Creek, Flying B, Thomas Creek, Indian Creek, and Upper Loon. The two most common errors new backcountry pilots make is to fly an approach that is too high and too fast, or to fly up or down the canyon out of sight of the airstrip, turn around, and drag the airplane in on a low, flat, blind approach. Both can be deadly, and both stem from a lack of application of basic principles that backcountry pilots consider second nature.

The first of these principles is an understanding of the relationship between airspeed and turn radius. Turn radius at any given bank angle is proportional to the square of the airspeed. By decreasing your airspeed you will reduce the area needed to turn in a canyon. For example, at 130 knots in a 30˚ bank, your turn radius would equal 2,599 feet, which means you would need almost one mile to execute a 180-degree turn. If the canyon you are flying in is only 3/4-mile wide, this could be deadly. Decreasing your airspeed to 70 knots will decrease your turn radius to 753 feet, which means you can turn 180 degrees in about one quarter mile, or in less than half the width of the same 3/4-mile wide canyon.

Generally, you will not want to exceed a medium bank when flying in canyons for several reasons. First, when maneuvering in a constricted canyon the terrain is above and beside you, and you will not have the visual horizon to which you are accustomed for reference; it can be disorienting, confusing, and deadly to “bank and yank.” Also, increasing your bank angle beyond 30˚ will rapidly increase the load factor and stall speed of the airplane. In addition, passengers don’t appreciate steep turns—especially in narrow canyons. Thus, slowing down is a key factor to flying in a constricted area and executing a good approach to a canyon airstrip.

Also paramount is the understanding of how to fly a power-on stabilized approach with a steep (4 to 4.5-degree) approach angle to a precise aim spot. The FAA defines a stabilized approach in the Private Pilot PTS as “an approach in which the aircraft is in a position where minimum input of all controls will result in a safe landing. Excessive control input at any point could be an indication of improper planning.” A major part of this planning is to determine what pitch and power settings will produce the best approach airspeed and pitch attitude for your airplane at a given weight and center of gravity. Sparky Imeson has a good discussion of this steep, backcountry approach technique in his Mountain Flying Bible. By approaching at a steeper angle you can clear obstacles, see the runway better, and be in front of the power curve instead of “dragging it in” on a long, shallow, slow, mushing approach. You will also have a shorter ground roll.

The FAA also states: “Experienced Pilots know the power settings and airspeeds for different landing weights, drag configurations and rates-of-descent for their airplanes” (FAA-P-8740-49). If you know how to listen, an airplane can “tell” you what airspeed, flap, gear, and power settings will work best at a given density altitude, weight, and center of gravity. Before venturing into canyon areas, you should seek out an experienced instructor who can help you with this. I generally work with a pilot through a series of maneuvers developed at our flight school to determine a good “canyon speed” for maneuvering in constricted areas, as well as the correct pitch, power, and airspeed to use for a stabilized approach in their airplane. Then we practice, practice, practice. Many backcountry airstrips are one way in and out, so once you are committed, there is no go-around option; you need to know ahead of time how you will set up and execute your approach.

To avoid flying approaches that are too high, use your altimeter. When approaching the landing area, slow to your canyon maneuvering configuration and airspeed. Circle the field at 800-1000 feet and check wind sock(s), look for game on or near the runway, check the runway surface condition, locate obstacles, note terrain surrounding the approach and departure paths, plan your departure, and locate any emergency landing spots to use in the event of an engine failure.

One of the first things my primary flight instructor told me was to always keep the airport within sight and within gliding distance—excellent advice. If you have the aircraft properly configured and established for a stabilized approach, flying a normal traffic pattern is straightforward at many backcountry airstrips. I have found the reason pilots are hesitant to “get down” into a canyon is a visual one. You must accept the fact that you will be flying much closer to the terrain than you are accustomed. Always remember that the worst place to fly is in the middle of a canyon; it leaves you no room to maneuver and you will encounter the worst turbulence, as well as create a collision hazard with other aircraft. Fly along one side of a canyon—preferably the downwind side—to give yourself maximum maneuvering room.

Avoid flying away from the airstrip and around a blind corner to return for an approach. A common place I see this is at Johnson Creek, where pilots descend over the town of Yellow Pine, more than three miles away, and enter a narrow canyon in a blind approach to the airstrip. When doing this, they cannot see or been seen by pilots flying a normal traffic pattern and they have no radio communications. I have flown normal traffic patterns resulting in a good 3/4-mile final at Johnson Creek in a myriad of aircraft, including Bonanzas, Mooneys, P210’s, and light to medium Piper and Cessna twin engine aircraft, so I know it is not necessary to fly around the corner to execute an approach.

The bottom line is, know your airplane, know yourself, and seek out someone with the knowledge and experience to help you maximize precision, control, performance, and safety when operating in mountain and canyon areas such as the Idaho backcountry.

Published in Pilot Getaways Magazine, 1999. Vol 2, issue 2, pg 54

By Amy Hoover. Published in Pilot Getaways Magazine, 1999

Summer is a time to slip the surly bonds and go on that adventure to the coast or to the mountains, to load up the family and make your way to Disneyland, or airplane camping and fishing in the wilderness. It is a time to use your craft in the myriad ways for which it was intended. But, when the mercury rises, you know your airplane just isn’t going to perform in the way to which you are accustomed, especially at higher altitudes.

At a given gross weight, increase in density altitude (DA) means a reduction in engine horsepower (thus a reduction in thrust), increased ground speed (thus longer takeoff and landing rolls), and decreased climb performance. The changes can be significant, especially at higher elevations.

A turbo-charger can solve some of the problems (except with your pocketbook). However, loss of propeller efficiency is a big factor, even on turbo-charged aircraft. If your summer flying takes you to the mountains, you will learn to operate in the morning or late evening when your engine, propeller, and wings perform better. A major item you can control is how you load your airplane; you determine is how you load your airplane.

When you operate at higher elevation airports in the heat of the summer, do you have a handle on how much weight reduction is necessary for safe operations? How often do you really know just what you can expect from your airplane at higher density altitudes? Your aircraft performance charts are a good place to start. However, many charts only give performance figures at gross weight, and some older aircraft substantial charts or data. Remember that you are not flying a new airplane and your performance will probably not meet the expectations of the charts.

An excellent method of determining effects of density altitude is to build your own performance charts. Load your airplane to different weight and Center of Gravity positions and record takeoff and landing distances at different density altitudes for each weight/CG combination. This requires some time commitment, but is worth it. Use a runway where you have references, such as spacing of runway edge lights, to be as accurate as possible in recording takeoff and landing distances. You may need to factor in other variables such as runway gradient, runway surface conditions, and wind. If you get the chance, attend a density altitude clinic, such as the ones sponsored by the FAA, to collect data on your aircraft performance.

Determining Density Altitude (DA):

Following is a simple way to determine density altitude (DA) at a given pressure altitude (PA).

Rule of thumb: To determine DA at a given PA, add 600 feet to existing PA for every 10° F above standard temperature for that altitude.To do this, you must know the standard temperature at a given PA as shown in the table below. You should know the standard temperature for your home field and other elevations you use often.

PA	ST (F)	ST (C)
Sea level	59.0° F	15° C
1000 feet	55.5° F	13° C
2000 feet	52.0° F	11° C
3000 feet	48.5° F	9° C
4000 feet	45.0° F	7° C
5000 feet	41.5° F	5° C
6000 feet	38.0° F	3° C
7000 feet	34.5° F	1° C
8000 feet	31.0° F	-1° C
9000 feet	27.5° F	-3° C

Here is an example using this simple rule of thumb. Suppose you want to depart from an airport at elevation 5000 feet on a summer day and the temperature is 85°F.

Example: 

Pressure altitude (PA)	5000 feet
Temperature	85° F
Standard temp at 5000 ft.	41.5° F
Temp	85 – 41.5 = 43.5° above standard

Using the Rule of thumb, round off the numbers to make it easier:

Density altitude (DA)	= 5000 + (600 x 4.4)
	= 5000 + 2640
	= 7600 feet

Thus, A typical summer density altitude in much of the mountain west is over a mile and a half high when you are sitting on the ground!

Another example:

PA	= 9000 feet
Temp	70° F
Standard temp at 9000 feet	27.5° F
Temp	= 70 – 27.5
	= 42.5 degrees above standard
Density Altitude (DA)	= 9000 + (600 X 4.3)
	= 9000 + 2580
	= 11,600 feet

In the mountains, where you will be flying at actual elevations ranging from over a mile to as much as 17,500 feet, increased density altitudes create a problem! Do you fly an airplane whose service ceiling is only a few hundred feet above the density altitude? What will your climb rate be? These are questions you should be posing when the temperatures start to rise. Having a quick idea of the density altitude is the best starting point. The next step is to determine…

Reduction in engine horsepower due to DA increase

As density altitude increases, engine horsepower decreases. If you know what the decrease is and how to apply that knowledge, you can determine roughly what your performance degradation will be and how much weight you may have to take out of the airplane to operate safely. The following is based on standard atmospheric pressure lapse rate and reciprocating engine efficiency

Rule of thumb: A normally aspirated aircraft engine loses approximately 3.5% hp per 1000 feet increase in DA.

Let’s use a common airplane as an example, a Cessna 182.

Example: 230 hp airplane at the 5000 ft airport where the DA = 7600 feet:

HP reduction	= 3.5% x 7.6
	= 27% reduction (approximately 73% available)
230hp x (73%)	= 168 hp available at 7600 ft DA

Another way to determine the amount of power reduction is to know what your engine will produce at full power on the MP gauge at sea level on a standard day. Then, determine the amount of power per inch it is producing, and calculate power reduction based on the fact the engine will lose one inch of manifold pressure per 1000ft DA.

Example: given a 230-hp engine that produces 28″ MP at full power, sea level standard day:

Horsepower per inch	= 230hp divided by 28″
	= 8.2 hp per inch

At 7600 ft DA the engine will produce approximately 20.4″ (28″ – 7.6″) at full power and the horsepower will be:

8.2 hp per inch X 20.4″

= 168 hp available at 7600 ft DA

Either of the above methods work in estimating your power reduction and give similar results. The amount of reduction may seem a shock at first, but it should alert you to the realities of density altitude related performance problems.

The next question is, how much weight must you remove to compensate for the reduced power if you want to operate at a roughly equivalent sea level performance? One way to do this is do determine the aircraft power loading at which you want to operate, and load the aircraft accordingly.

Power loading and weight reduction

Sea level standard day power loading is defined as gross weight (GW) divided by horsepower available. In many of the newer Owners manuals or Pilots Operating Handbooks sea level power loading is given with other performance figures, but it is easy to calculate. Using the Cessna 182 again:

Example: The Cessna 182 is A 2950-lb, 230-hp airplane at sea level:

Power loading	= 2950lb……= 12.8 lb/HP
	= 230HP

To get sea level power loading out of the airplane at higher density altitudes, you would have to remove enough weight such that the new weight to hp ratio equals 12.8 lb/HP. To do this, first compute net HP for density altitude:

From the previous example	5000 ft PA and 85° F
Density altitude	= 7600 ft
Horsepower available	= 168 hp
Original (certified) GW	= 2950 lbs

To calculate the “effective” gross weight that will give equivalent power loading, multiply the net HP available by the desired sea level power loading:

net HP available x SL power loading	= new GW
168hp x 12.8	= 2150 lbs

Thus to obtain sea level equivalent power loading for the Cessna 182 on a summer day at 5000ft elevation and 85° F you must remove roughly 800 lbs!! That is equivalent to two 180-lb passengers, two 75-lb bags, and 48 gallons of gas!

The calculation may be done using any power loading you choose to get an approximation of the expected performance. For example, if you usually operate from a 3000-ft elevation airport and the performance there is adequate, simply calculate the power loading using 3000-ft pressure altitude and standard temperature, and use that figure as the standard of comparison.

Aircraft loading and weight are items over which pilots have direct and immediate control. We have looked at how to reduce aircraft weight to get better performance. However, you may choose to fly with a given weight and accept the decrease in performance. If so, you should have a good idea of just what that decrease in performance is going to be. If an aircraft has inadequate performance charts, you may choose to make your own, as suggested earlier. Or, you may have to make some choices, such as flying only in the morning or evening, or making multiple trips carrying lighter loads.

The bottom line is, be aware of the effects of density altitude on the performance of any aircraft, and learn to lighten up!!

Published in Pilot Getaways Magazine, 1999. Volume 2, issue 3, pg 45

By Amy Hoover. Published in Pilot Getaways Magazine, 2000.

You roll out high and hot on final and just know you can save this landing; you could point the nose down, suck the throttle back, dive toward that midfield taxiway, and hope for the best.  Or you could abort the landing and execute a go-around. A go-around is a viable option for almost any approach, with the exception of landing in confined areas at one-way airstrips or at very high density altitudes.  However, pilots typically get into go-around trouble by making a poor decision, a latent decision, or by indecision.

Reasons for aborting a landing include other airplane traffic in the pattern or on the runway, ATC instructions to go around, a destabilized approach due to misjudging wind or to poor aircraft control, excessive floating, or a bounce or “botched” landing. In all cases, the earlier the go-around decision is made, the larger the safety margin will be for its execution.  In addition, the decision should be positive and the go-around should be executed without hesitation once the decision is made.

Does your pre-landing checklist include identifying results of possible go-arounds from different positions throughout the approach and landing? It should. When you study an airport layout during your preflight, and when you enter the traffic pattern, assess items such as surrounding terrain and obstacles, the departure path, and the airplane’s climb performance in the landing configuration.  Also, determine how density altitude will affect power available, groundspeed, and the airplane’s climb capability. Decide in advance at what point a go-around would become potentially hazardous and make a firm decision to abort the landing if criteria such as airspeed, altitude, and proper spacing from the runway are not met at certain “key” positions in the landing pattern. For example, If you are way too high and too hot in the turn from base to final, that is the time to go around if terrain and traffic permit.  Failure to make a positive decision, and to make it early, could result in a long landing with insufficient room to stop, or a latent decision to go around from a position too far down the runway to be safe. By choosing your action in advance, you are removing the element of indecision.

Go-arounds from a botched landing pose additional problems.  A typical bounce results from excessive airspeed, which usually results from a fast approach. If you are too hot on final approach you should ask yourself, “Would I takeoff in the landing configuration from that mid-field intersection?” because that is what you will be attempting to do if you float or bounce and go around.   It would be better to ground loop, run off the end of the runway, or run into obstacles on the ground than to attempt a go-around too late and hit obstacles, trees, or terrain while airborne, or to enter a departure stall, both of which can be deadly.

A few months ago a veteran pilot in the local area attempted to land with a tailwind.  The plane landed long and the pilot executed a go-around. Eyewitness said the plane bounced, went to full power, the nose pitched up radically, and the plane stalled and nosed over, killing the pilot in the post-impact fire.  The NTSB reported the airplane had full flaps with nose up trim. This situation represents a real snake in the grass called an “elevator trim stall”. For some airplanes set to the landing configuration and trim, application of power causes an enormous nose up pitching moment, which the trim setting exacerbates. The pilot may have to really shove forward on the yoke or stick to avoid a stall.  In a heavily loaded airplane with an aft CG the force may be too great for the pilot to overcome. In addition, an immediate and strong application of right rudder might also be necessary to avoid loss of directional control.

In a go-around you are not just starting a climb, you are transitioning from a descent to a climb, which could take a considerable amount of time and distance.  The key is to decide early, make a positive decision, and implement it without hesitation before a critical situation develops. Plan ahead and practice the actual sequence in which you will execute each part of the maneuver in your airplane.  For example, a typical scenario would be to simultaneously add power, right rudder, and push forward on the yoke or stick, retract flaps incrementally to takeoff setting after the descent is arrested, trim to relieve control pressures, then retract landing gear after a positive rate of climb is achieved.  

It is essential to practice the go-around transition sequence at different weights and center of gravity positions so you will know what to expect.  Take the airplane to a safe altitude, but one that is close enough to the airport elevation you will be using so you will have similar power and P-factor effects (regulations specify 1500 feet AGL for recovery from maneuver).  Set the plane up for a normal approach descent with gear and flaps down and trimmed for landing, then add full takeoff power and note several items, including: 1) how much forward force you must apply to the yoke or stick to avoid a departure stall; 2) altitude loss from the time of power application until you arrest the descent and initiate a climb; and 3) the time and distance it requires to transition from the descent to the climb. Do the transition to best rate and best angle of climb speed and note differences needed in control pressures and pitch attitude.  Then do some transitions “hands off” and let the plane enter a departure stall on its own; which may surprise you.

All too often a go-around is executed as a “knee-jerk reaction” type of maneuver, which can have disastrous results. By planning ahead you can add go-around safety to your flying mind set.  Consider any go-around to be an emergency procedure; plan for it, practice it, and use it wisely.

Published in Pilot Getaways Magazine, 2000, Volume 3, issue 2, pg. 54

By Amy Hoover. Published in Pilot Getaways Magazine, 2001.

Many pilots sweat the approach and landing to an unimproved, high mountain airstrip and are gratified by a safe arrival. But how much thought has been given to departing that grass or dirt strip at 7000 feet elevation with high terrain lurking in all quadrants? Experienced mountain pilots treat takeoff and departure from high elevation unimproved airstrips as the most critical phase of flight.

Typical summer afternoon Density Altitude (DA) can easily exceed 10,000 feet at many mountain strips, and the associated decrease in airplane performance is enormous. The takeoff ground roll at high DA is significantly increased due to reduced engine power, loss of propeller efficiency, and higher groundspeeds. Grass, dirt, sand, and gravel can greatly lengthen the takeoff roll. Climb performance is also drastically reduced.

Takeoff

The best technique is a combination short-soft field takeoff. Holding brakes while applying maximum power is not recommended when operating from unimproved strips; it can throw rocks and debris into the propeller, fuselage, and horizontal stabilizer. It is best to keep the airplane moving smoothly from taxi to takeoff roll and avoid sudden bursts of power. An engine check can be done during taxi, or by doing a runup at a spot with minimum debris.

For tricycle gear aircraft, use just enough back pressure initially to lighten the nosewheel as soon as possible and let the airplane fly itself off the runway and into ground effect. In most taildraggers, let the tailwheel come up when it is ready and takeoff tail low, allowing the airplane to fly itself off. Both nosewheel and taildragger pilots who have no experience with high altitude takeoffs are usually amazed at how long the airplane takes to accelerate.

However, at high DA indicated airspeed will be lower than groundspeed, giving a false sense of acceleration. A common and dangerous mistake is to over-rotate in an attempt to force the airplane off the runway when the pilot “feels” the airplane is ready. Over-rotating can cause the airplane to climb out of ground effect, stall, and drop back onto the runway, which can eat up a lot of needed real estate during the takeoff roll. Patience is the primary skill needed to perform a high DA takeoff, especially from a soft field.

After breaking ground, reduce the angle of attack and accelerate to climb speed in ground effect. This will transfer the weight from the wheels to the wings as soon as possible without increasing the angle of attack (which increases drag). The key is to find and hold the correct angle of attack for minimum drag while the plane is accelerating in ground effect.

A good general rule of thumb is: if you can’t see the end of the runway over the nose of the airplane, the angle is too high. When the wing reaches the correct airspeed the airplane will begin to climb with only minimal, if any, change in pitch attitude or pressure on the yoke or stick. This technique minimizes takeoff roll and maximizes safety by allowing the airplane to fly itself off without the pilot forcing it to rotate before climb speed is obtained.

Departure

Pilots new to high altitude flying may become alarmed at the enormous reduction in climb rate and try to milk a climb out of the airplane by continuing to pull back and increase the pitch attitude, resulting in a dangerously low airspeed, increased drag, and an incipient departure stall. Pitch attitudes for best angle (Vx) and best rate (Vy) of climb airspeeds are much flatter at high DA than at sea level. It is imperative to learn the correct pitch attitude for the aircraft’s climb speeds at higher DA and to vigilantly reference the airspeed indicator. The same rule of thumb applies: if you can’t see the ground over the nose, lower the pitch attitude.

During initial climb, use normal power, propeller, and flap settings recommended for the aircraft. Maintain Vx until clear of obstacles, then accelerate to Vy or cruise climb, as appropriate. When possible, cruise climb is recommended as it provides better forward visibility and allows for increased engine cooling. Changing aircraft configuration while climbing at low altitude over obstacles can be distracting and potentially dangerous.

Concentrate on climbing and maneuvering before decreasing power or retracting flaps, particularly in canyons or confined areas. In complex aircraft, know the amount of drag reduction and the retraction time for landing gear. If there is no significant reduction in drag, it may be best not to change propeller, gear, or flap settings until clear of obstacles and established in a positive climb. In some aircraft, such as a Cessna 210, retraction of landing gear may create significant drag while in transit, which could cause the aircraft go from a climb to a descent and settle back to the ground or into an obstacle. 



A normal traffic pattern departure may not be possible at mountain airstrips; terrain, wind, sun angle, turbulence, and locations of lift or sink may determine the desired departure path. A prepared pilot will study and plan the departure while circling the area during the approach, including the location of emergency landing spots along the departure route.

Abort Point

A takeoff abort point should be determined at any high altitude airstrip. On airstrips without gradient, a general aviation airplane must attain 70% of it’s liftoff speed halfway down the runway for a successful takeoff. If you have not attained that speed prior to the halfway point, the takeoff should be aborted. Stopping may not be possible on slippery surfaces, very short strips, or strips with a downhill gradient. In such cases, make a mental note that an abort is not possible and be prepared for emergency options, especially with regard to emergency landing spots along the departure path.

The best way to determine a takeoff abort point is to walk the airstrip. Look at the runway surface and note obstacles, holes, ditches, soft spots, and places to avoid during the takeoff roll. Pace the runway off and determine the midpoint, or determine how much runway is needed to stop safely and choose an easily identifiable visual abort point. Make the decision to abort the takeoff if the airplane is not in ground effect and accelerating, with engine instruments indicating full power, by a certain prominent rock, stump, tree, bend in the strip, windsock, etc. that was chosen while walking the strip. Most importantly, after choosing the abort point, use it!!



The procedures for soft field takeoffs change when the temperatures rise and altitudes increase. By adjusting your procedures accordingly, you will be able to safely enjoy the many rewards of flying to high mountain or remote canyon airstrips.

Published in Pilot Getaways Magazine, 2001. Vol 4, issue 2, pg 58.

By Amy Hoover. Published in Pilot Getaways Magazine, 2001.

With an understanding of a few basic “rules”, canyon flying can be exciting, challenging, fun, and above all, safe.

Rule #1: Slow down and use medium bank turns

Flying slowly in a canyon is critical to safe operations because it gives the pilot more time to react and is the best way to decrease turn radius while maneuvering.  Pilots need to keep their head “out of the cockpit” when flying in canyons and confined spaces, thus it is critical to know the correct power settings to achieve a desired airspeed, such as maneuvering speed (V_A), or maximum flap extended speed (V_FE).   Rattling around in a narrow canyon is not the time to be distracted by hunting for power settings, so pilots should prepare by determining the correct “target” power settings and airspeeds ahead of time.  The power required to maintain a given airspeed in level flight depends on weight and position of the center of gravity (CG), with more power required as the airplane gets heavier and the CG moves forward.  To determine the correct power settings to use, load the aircraft to the desired weight and CG position and go flying. Maintain altitude while reducing power until the desired airspeed is obtained, and record the power required.  Make some medium bank turns at your chosen airspeeds while holding altitude to determine whether additional power is needed in the turns. Keep in mind that the pitch attitude might have to decrease slightly in a turn to maintain airspeed.  By determining target power settings in advance, the pilot can slow down to a desired airspeed smoothly and with confidence while maintaining situational awareness in a canyon.

At a given airspeed, the steeper the bank angle, the tighter the turn.  Tighter turns are needed in confined areas, but steep turns in canyons can lead to many problems, including visual disorientation.  In a canyon there may be no horizon to reference airplane attitude, so shallow to medium bank angles greatly decrease the risk of becoming disoriented.  Also, increasing bank angle beyond 30° rapidly increases the load factor and stall speed of the airplane (both increase as the square of the airspeed). The best way to avoid disorientation and “pulling G’s” that could stress the airframe and increase your stall speed is to limit bank angles to 30 degrees.

By combining these two axioms a pilot can maneuver or turn around in a relatively narrow space.  But how much should the airplane be slowed down? For example, suppose a pilot is flying in a canyon and needs to turn around safely to avoid weather, hazards, or to circle over an airstrip to check out the conditions.  For operations in canyons more than 3/4 mile wide, V_A is generally a good target airspeed in most general aviation aircraft.  However, in narrow canyons a good technique is to slow to V_FE  and extend flaps to stabilize the airplane. Reference the Pilots Operating Handbook to determine the flap setting recommended for a maximum performance takeoff.  That setting generally gives the maximum lift to drag ratio for the wing, and is the best flap setting to use for slow flight in a canyon. For most general aviation airplanes, a power setting somewhere around the bottom of the green arc on the manifold pressure gauge will yield a speed between 70 and 90 knots at takeoff flap setting. Use of full flaps is not recommended as it creates a lot of drag and requires more power.

Here’s an example.  At a given bank angle turn radius varies directly as the square of the airspeed.  For an airplane with a cruise speed of 140 kts, in a 30° bank, turn radius will be:

That is equal to a turn radius of over half a mile, so it would require twice that distance, more than a mile, to execute a 180° turn at a cruise speed of 140 kts in a 30° bank.  In a narrow canyon, the pilot would have to make a steeper bank turn to execute the maneuver and be subjected to the aforementioned hazards of steep banks.  However, at a little over half that speed, or 75kts, the new turn radius would be:

Now the 180° turn can be executed comfortably and safely, while still maintaining a medium 30° bank turn, in 1700 feet, or 1/3 of a mile.  Turn radius calculations are mathematically correct, but will vary depending on pilot technique (maintaining a constant bank angle and airspeed).  Wind and varying groundspeed will affect turn radius with reference to the ground (or canyon wall), leading to the next rule:

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Rule #2: Fly in smooth air

When there is a lot of wind or turbulence in canyons, professional pilots are usually back at the hangar drinking coffee.  Canyon winds can be unpredictable, and it is generally prudent to avoid flying in high winds or turbulence. Another, possibly not so intuitive, reason is that when flaps are lowered as suggested to slow and stabilize the airplane, the limit load factor of the wing may be drastically decreased.  For example, the airplane might be certified for 3.8 positive G’s, but with flaps down may only be certificated for 2.4 G’s. Thus, slowing down and using flaps to maximize safety could compromise the structural integrity of the airframe in turbulence.

Rule #3: always remain in a position to turn toward lowering terrain

This means flying along the side, not in the middle, of a canyon and being aware of the “escape route” at all times.  In general, try and fly downstream (downhill) in canyons and follow drainages that have large rivers or streams in them; the canyons will be wider and gradients shallower, and the terrain less likely to rise more steeply than the climb performance of the aircraft can handle.  The “old and not so bold” bush pilots say, “always have a back door”. These simple rules help to keep a pilot’s hand on the doorknob!

Published in Pilot Getaways Magazine, 2001. Vol 4, issue 4, pg 62

By Amy Hoover. Published in Pilot Getaways magazine, 2002.

Airstrips located atop mesas, in hill country, in canyons, or along rivers may have a gradient varying from small to significant. Wind permitting, it is generally best to land uphill and takeoff downhill. With a little practice, approach and landing to uphill airports can be accomplished without much difficulty, and most pilots find the ground roll delightfully short (landing uphill on very steep runways requires special techniques outside the scope of this article). However, as runways get steeper, shorter, and higher, planning for approach, landing, takeoff, and departure becomes more critical. Knowing the effects of runway gradient on takeoff and landing performance will give the pilot an extra safety margin, especially when deciding whether a takeoff would be prudent with a given aircraft weight, wind, and density altitude.

Runway Gradient

It may not be possible to accurately judge gradient when checking out an airstrip from the air. This means information from airport directories or local knowledge gleaned from pilots familiar with the landing area is invaluable. Once on the ground, there is a way to calculate runway gradient using the aircraft altimeter and a little legwork. Here’s how: taxi to one end of the runway and read the elevation from the altimeter, then taxi to the other end and find the elevation there. The difference in elevation between ends divided by total length equals the gradient. If there is no published runway length, pacing off the strip can give a fairly accurate measurement.

Example: A pilot lands at a beautiful mountain airstrip in a meadow next to a world class trout stream. She wonders whether or not a mid-afternoon takeoff is possible, and how much fish she can catch and take home. Some Pilot Operating Handbooks (POH) include factors for gradient in their performance charts, but some do not, including hers. The pilot paces off the airstrip and determines it to be approximately 2500 feet long. The altimeter difference between ends is:

High end:	4285′
Low end:	4210′
	=.75′ difference in elevation between ends
75′ X 100%	= 3% gradient 2500′

Now she has some parameters to work with

Runway length	= 2500 feet
Runway gradient	= 3%

Because the pilot is taking off downhill, the effective runway length will be longer than the actual length. Using the following rule of thumb, she can determine her effective runway length for takeoff (downhill) and landing (uphill):

Rule of Thumb: When computing runway gradient, every 1.0% grade equals approximately 10% change in effective runway length

3% gradient	= 30% increase in effective runway length
	= 2500′ + (.3 x 2500)
Effective length	= 3250 feet

The pilot can then refer to the POH at the correct density altitude to see how much fish she can safely carry. If she took off uphill, or landed downhill, the runway would be effectively shortened by the same amount. Keep in mind that this is only a rule of thumb, and will vary depending on the thrust/drag relationship and weight of the airplane. Additionally, the gradient may not be uniform along the entire length of the runway, with some sections steeper than others.

When the wind blows

In an ideal world, pilots would always be able to land uphill with a headwind and takeoff downhill with a headwind. But what about the times when gradient and wind are in “opposition”? Which is best, landing uphill with a tailwind, or downhill with a headwind? Is it better to takeoff downhill with a tailwind, or uphill with a headwind? Let’s look at some of these scenarios.

Landing uphill with a tailwind

Planning to land with a tailwind should be done with caution. A 10% increase in groundspeed results in a 20% increase in landing distance, so that even light tailwinds can greatly increase the landing ground roll. If the runway ends in a drop-off, such as on top of a mesa or along a riverbank, and a landing is made with a tailwind, one should anticipate an updraft over the drop-off on short final. This updraft can cause the airplane to balloon or float further down the runway before touchdown, and could be problematic depending on runway length and gradient. Additionally, when landing with a tailwind the pilot will have to fly a steeper approach to compensate for increased groundspeed, which can cause visual illusions that hinder judgment of height and distance relative to a sloping runway.

Landing downhill with a headwind

A strong headwind is required to overcome the increase in landing roll that a downhill landing creates; if the wind is strong enough to cancel the effects of a large downhill slope, expect a lot of turbulence on the approach, particularly if there are obstacles or trees. If the approach is flown at a faster airspeed to compensate for gusts and turbulence, the increase in groundspeed will lengthen the landing roll. Also, when landing downhill the plane will float, and float, and float. Pilots may find it hard to touch down because the ground keeps dropping out from under the airplane. Once on the ground the pilot is counting on brakes to stop (going downhill). Heavier airplanes have more inertia and can be hard to stop.

Taking off downhill with a tailwind

Because a 10% increase in groundspeed increases the takeoff roll by 20%, and every 1.0% of runway downslope equals approximately 10% more effective runway, it takes about 1.0% downslope to counter every 2-3 knots of tailwind for most general aviation aircraft. Thus, a 6-10 knot tailwind would require at least a 3.0% downslope to neutralize the effects of wind. If the downsloping runway ends in a drop-off, the plane may become airborne or fly in ground effect, but will encounter a downdraft over the drop-off once it leaves the runway. Turbulence will often accompany this downdraft, and water will amplify it. This can be a sticky situation, especially when launching off a mesa or a strip in a river canyon. If no turns can be made and the departure must be flown with a tailwind due to terrain, downdrafts and turbulence may continue along the departure path. The only option a pilot has is to lower the nose and maintain airspeed.

Taking off uphill with a headwind

Based on the relationships of groundspeed and gradient, an airplane will generally require a significant headwind to counteract more than a slight uphill slope. If the runway is short, choose a takeoff abort point; if the airplane is not in ground effect and accelerating by that point it may not outclimb the gradient. Aborting a takeoff uphill provides more rapid deceleration and less distance than a runway without slope. Anticipate wind shear and turbulence over trees or obstacles after departure. Also, when taking off uphill, chances are the terrain beyond the departure end of the airstrip rises, and may exceed the climb capability of the aircraft.

Use caution when mixing wind and runway gradient. Many times runways with gradient have surrounding obstacles and terrain that can exacerbate the effects of downdrafts, wind shear, and turbulence on approach and departure. On short runways, especially with obstacles in the approach or departure path, landing and taking off with more than a light wind may not be a good idea.

Published in Pilot Getaways Magazine, 2002. Volume 5, Issue 2

By Amy Hoover. Published in Pilot Getaways Magazine, 2004.

The previous article, Canyon Weather Part 1: The Effects of Wind and Sun, discussed how wind, sun, and terrain can dramatically affect weather in canyons. This article explores more phenomena unique to canyon flying, including how different winds interact with each other, and where and when to expect turbulence.

It is important to understand these interactions because many mountain airstrips are in canyon bottoms or on ridges that separate canyons. Even if you’re not flying to such airstrips, canyons typically constitute the lowest route through the mountains and provide more emergency options. Additionally, you may have no choice but to fly in canyons, since the elevation of the surrounding mountains may exceed your aircraft’s service ceiling.

Diurnal Effects

As discussed in the previous issue, uneven heating of the Earth’s surface is what drives weather processes. Several factors such as varying slope, color, latitude, and elevation contribute to uneven surface heating. Many canyons are hundreds of miles long and the elevation between their upper and lower ends may differ by thousands of feet. Changes that occur on a daily cycle in these deep, long canyons are the result of the interplay between heat from the sun, rising and falling air, and the shape and elevation of the terrain. These daily changes are called diurnal effects, and are greatest in the summer months when the sun is highest and the days are longest. When the morning sun strikes canyon walls, it starts a thermal heating process: air from the lower part of the canyon heats up and begins to rise. The rising air simply follows the canyon upstream. Thus, canyon breezes normally blow up-canyon (or upstream) beginning midmorning. These winds can become quite strong by midafternoon.

During evening hours the air cools off more quickly at the upper (higher altitude) end of a canyon. This cooling air becomes dense and sinks downstream. Thus, canyon winds normally flow down-canyon (downstream) during evening and nighttime hours. This cycle of winds blowing upstream in the mornings and downstream in the evenings is a dynamic process that repeats daily, but there can be many exceptions locally due the shape of the canyon itself, as well as the influence from winds entering the canyon from tributary canyons.

Convergence Effects

A phenomenon that occurs where canyons join is called a convergence effect. Canyons may converge at various angles and in varying directions. Diurnal winds may be stronger and develop early in the day in large canyons, but may develop later, or not at all, in smaller tributary canyons. This means the wind might be blowing upstream in the main canyon but blowing downstream in one of the side canyons that feeds into the main canyon. Flying past this confluence, you should expect turbulence, which could be severe, depending on the relative strength of the opposing winds. When planning a flight into mountain and canyon areas, you should study your aeronautical chart and pay special attention to areas where canyons converge, so you can anticipate turbulence and plan your route and altitude accordingly.

Because of converging rivers or streams, canyons are typically wider at confluences, and sandbars or benches tend to form there. Thus, airstrips are often located near river confluences. If you are operating at an airstrip near a confluence, be alert for varying winds, wind shear, and turbulence. Many canyon airstrips have more than one windsock to help you determine the effects of converging winds. It is not unusual for these windsocks to point in opposite directions, even though they are only a few thousand feet apart. If the converging canyons are not deep, winds can converge over the top of the ridge that separates them; if an airstrip is at the top of such a ridge, beware of wind shear and turbulence.

Venturi Effects

The venturi effect is an increase in wind speed through a constriction or bottleneck, such as a narrow mountain pass or a narrow spot in a canyon. If a large open valley or intermountain basin narrows to form the entrance to a canyon, the wind will accelerate as it passes into the canyon, causing a decrease in pressure, which creates a downdraft. The downdraft can be insidious, as there may not be a lot of turbulence associated with it. Alternatively, when a wind is blowing up or down a canyon that opens out into a wide valley, the wind will diverge and typically flow outward away from the constricted area, which can cause wind shear in horizontal and vertical directions. When studying your charts during preflight planning, note any such constric- tions and anticipate a venturi effect. You might also expect a venturi effect in a narrow canyon that makes a sharp bend, caus- ing the wind to change direction rapidly.

Turbulence

Turbulence can make any flight uncomfortable, and could damage your aircraft. Throughout this two-part discussion, we noted situations and locations in which a pilot can expect turbulence when flying in mountains and canyons. On this page is a summary of where you should expect turbulence, which should help you in your quest to avoid it.

Turbulence is Found:

• On the lee side of mountain ridges 
• Near abrupt changes from sunlit to shaded or wooded to bare terrain 
• Along ridges that separate canyons that are not connected 
• In canyons when the winds aloft exceed 15–25 knots 
• In canyons where orographic and thermal effects are in opposition 
• In convergence areas (at the confluence of two drainages) 
• In areas where a valley narrows to a canyon, or where a canyon narrows or shows a radical change in direction

You should be constantly vigilant for phenomena such as convergence and venturi effects and learn to anticipate areas of turbulence. It is best to seek out updrafts, avoid downdrafts, and try to stay out of turbulence. Often lift is where you find it, so you should actively seek out updrafts and always be wary. Although we have looked at some general rules pertaining to wind, lift, and turbulence when flying in canyons, it is best to expect the unexpected. If the winds aloft are strong, you should reassess your flight plan; you may need to change your route of flight, your altitude, or postpone your flight. Knowledge of these phenomena can help make your mountain and canyon flying safe and enjoyable.

Published in Pilot Getaways Magazine, 2004. Vol 7, issue 2, pg 82

By Amy Hoover Published in Pilot Getaways Magazine, 2004.

Mountain flying often requires flights through deep, winding, sometimes narrow, and randomly oriented canyons. You might fly to an airstrip in the bottom of a canyon, or on top of a ridge or mesa. Or, you might just need to fly through the canyons to get to your destination. In any case, how do you prepare for Mother Nature’s challenges? Primarily, you need to anticipate where air currents will be. The first step, of course, is to get a thorough weather briefing. However, the weather synopses provided by the briefer may not adequately prepare you for the weather factors and phenomena specific to canyons along your route of flight.

Deep canyons can effectively separate landing areas that may only be a few miles apart, so weather can vary greatly over a small distance. The factors that affect weather are often very localized, so a flight service station may have no insight into the weather in a particular canyon. When flying in a new area, knowledge from local pilots is invaluable.

If two canyons are in the same drainage system, pressure usually equalizes quickly between them and the altimeter setting is nearly uniform. However, local winds and pressure patterns can be very different in river drainage systems only a few miles apart. If you fly from one canyon across a ridge into a different canyon that is not connected, there may be a pressure differential between the two canyons. In that case, you can expect wind and turbulence at the divide between the two drainage systems. The different pressure in the new canyon may cause your altimeter to be off by several hundred feet until you get a new altimeter setting. All pilots share the same problem, so be aware that other airplanes may be reporting altitude with a different altimeter setting from yours. Set your altimeter to the field elevation each time you land, and verify altimeter settings with other pilots when passing.

If you’re heading toward a region with lower pressure, your actual altitude will be lower than your altimeter indicates. Remember the adage “high to low, look out below,” and don’t necessarily trust an altimeter setting, particularly when a storm approaches.

No Lift Is a Drag

In mountains and canyons, you must know where to find lift and how to use it to your advantage. Fly on the updraft side of ridges and canyons, where there is lift to improve climb performance and terrain clearance. On the downdraft side, you may find a rough ride and downdrafts that exceed the climb capability of your aircraft. Most mountain pilots expect wind to flow down into a canyon and then up the other side, creating an updraft on the downwind side of the canyon. However, that’s not always true since actual lift is the result of the interaction between orographic lift (wind) and solar lift (heat). Additionally, the updraft side may change from one side of the canyon to the other as the canyon twists and turns and different sides face the sun or wind.

Orographic Lift

Orographic lift is mechanical lift created by wind flowing over terrain. In North America the prevailing winds are generally from the west, so you can usually find upslope winds on west facing slopes and downslope winds on east facing slopes. This is especially true with well- defined, north-south mountain ranges perpendicular to the prevailing winds, such as the Cascades, Sierra Nevada, or Rocky Mountains.

In areas where more randomly oriented canyons prevail, determining local wind directions and locations of orographic lift are not straightforward. For example, the mountains of central Idaho are formed by a large mass of random ridges cut by deep, twisting drainages. When winds flow over them, the effect is similar to ocean waves crashing over a jumble of rocks: chaotic, unpredictable areas of lift and sink, and greatly varying local winds. Midlevel or ridge top winds can also vary widely and be hard to predict.

Solar Lift

Sunlit slopes heat up more quickly than the surrounding terrain, causing thermal, or anabatic, lift. Mountain pilots seek out this lift, since it can be quite significant. Early morning lift on east-facing slopes is usually weak and short-lived, but you’ll find better lift later in the day on south- and west-facing slopes that have had adequate time to heat up. Thermal lift usually extends only 50 to 200 feet out from mountain ridges or canyon walls, and is also found directly above ridgelines. This means you need to fly close to the faces of mountains or canyon walls to use thermal lift. Bare rocks and slopes heat up faster and generate more lift than heavily forested areas, so look for the “brighter” slopes. In fact, there may be enough difference in lift between bare slopes and forested areas to cre- ate turbulence at the boundary between them due to the wind shear produced by differential lift. Likewise, expect to find turbulence at the boundary between areas that are in sun and areas in shadow.

Combinations of Lift

In summer when the sun is shining on southwest- and west-facing slopes and the wind is also out of the southwest or west, orographic and thermal lift can combine, which greatly augments the lifting force. But what if the wind is blowing from other directions? If thermal and orographic lift work against each other, the results can be much different, depending on wind velocity. Thermal lift will create updrafts on a sun-facing slope, but if that slope is on the lee side of a ridge or canyon, orographic effects produce downdrafts. The updrafts meet the downdrafts and create turbulence. As wind velocity increases, this turbulence reaches deeper into the canyon and can become severe to extreme. In very deep, rocky canyons that are exposed to the sun for a long time during summer days, thermal lift may cause updrafts powerful enough to create a “cushion” of air in the canyon bottom that deflects the orographic downdrafts. This may result in turbulence at any level in the canyon depending on the relative strength of the opposing thermal and orographic effects. Such turbulence is often greatest at ridge top level. Solar lift on the upwind side of the canyon may be stronger than orographic lift on the downwind side of the canyon, depending on temperature and geographic location, thus making it better to fly on the upwind, or “wrong,” side of the canyon.

Predicting which of these phenomena will occur is difficult, so it is best to stay out of canyons when the wind is blowing strongly. You’ll find local pilots to be a great resource, since they know where and when to expect turbulence and lift. It may be safe to fly with winds of 15–20 knots in one area and not in another.

Just when you think you have figured out the effects of wind and sun, and you can find lift, you may encounter some other canyon beasts like diurnal winds, venturi effects, and convergence effects to shake up your flight. 

Published in Pilot Getaways Magazine, 2004. Vol 7, issue 1, pg 82