box canyon turn

No one should need the box canyon turn under normal circumstances. If you need this manoeuvre, you have violated the laws of mountain flying.

To explain the box canyon turn it is necessary to consider two scenarios. In the first, the pilot is flying along at cruise power setting and cruise airspeed. In the second case, the pilot is flying at minimum controllable airspeed. This minimum controllable airspeed is probably not an intentional flight condition.

Flying over water beyond the power-off gliding distance from the shore, sometimes causes the oil pressure gauge to begin ticking. And it hasn't done that before. Next the engine may appear to give a little shudder of roughness. This might happen several times before you again approach the safety of the shoreline.

A similar phenomenon occurs when flying upslope terrain in the mountains. Your left arm becomes shorter. This is a normal self-preservation aspect of flight. You unconsciously pull away from the rising terrain and often the deterioration of airspeed goes unnoticed.

Conditioned Response

Mountain flying, like Mother Nature, can be harsh and unforgiving for the novice who fails to adhere to the two basic premises for all mountain flying: It’s really a simple matter to flirt with the mountains if you always remain in a position to be able to turn toward lowering terrain and never fly beyond the point of no return.

The first law, being able to turn while having some extra altitude to descend, does encompass the idea that you never enter into a canyon if there is not sufficient room to turn around.

The second law, to never fly beyond the point of no return, requires the pilot to establish a turn-around point whenever flying upslope terrain. The point of no return is defined as a point on the ground of rising terrain where the terrain out climbs the aircraft. The turn-around point is determined as the position where, if the throttle is reduced to idle, the aircraft can be turned around during a glide without impacting the terrain. Obviously, the power is not reduced to idle. This merely is a gauge to judge and establish the point over the ground where an escape turn must be made.

For the unconcerned aviator bopping along through the mountains at cruise power setting, it is still necessary to maintain a conditioned reflex of maintaining a position where you can always turn to lowering terrain and never fly beyond the point of no return.

This must be a conditioned reflex rather than instinct, because instinct is often wrong in an airplane. For example, if you have ever experienced a spin, your first impression is that the airplane is pointing straight towards the ground while rotating. The Cessna 172, for example, has its nose 46 degrees below the horizon, only about halfway from the horizon to the vertical. Your instinct will be to raise the nose with back pressure. It's always worked before. But now you must use the conditioned reflex of relaxing the controls (or pushing the controls forward) to break the stall and then fly out of the resulting dive without exceeding the critical angle of attack (somewhere around 16-18 degrees).

Another example of the conditioned reflex is the forced landing procedure experienced at the beginning of the private pilot training. After several lessons, the flight instructor reaches out and pulls the power lever, stating something like, "You're engine just quit, proceed as you would in an actual emergency."

To begin, your first endeavours don't provide much satisfaction for yourself or the instructor. You try to pick out an area for a forced landing and next try to extend the glide to make it to that spot; however, without experience only luck will allow you to approach anywhere near your projected spot.

If you have an excellent flight instructor, someone who teaches the spot method of landing, it is easy to determine how far the airplane will glide. Using the spot method technique allows you to look at a windscreen mark during a glide and determine the spot on the ground where the airplane will glide. By mentally subscribing a line in an arc from this point, the area surrounding the airplane within which the airplane can be landed is defined.

The instructor continues this "conditioning," much as Pavlov conditioned his dogs, but hopefully without quite as much salivating. At some point during this process, your subconscious begins mentally picking out forced-landing areas. When the conditioning is complete, the instructor pulls the engine power and you, without really thinking or concentrating about it, head for a forced-landing spot. The spot may be ahead or behind the airplane, it doesn't really matter for your subconscious has already made the decision.

Until you have practiced the box canyon turn and understand the mechanics of and the ramifications of an unintentional stall close to the terrain, the best advice for escaping from a "tight," or rapidly rising terrain or the narrowing confines of a canyon, is to make a steep turn at a slow speed, using flaps if prudent.

What possible options are available for the course reversal manoeuvre to escape the precarious position?

Hammerhead Turn

Pilots, in all seriousness, have asked my advice about performing the hammerhead turn as an emergency procedure for getting out of a tight spot. There are several problems that immediately jump to mind, negating the possibility of performing the hammerhead turn.

First by way of definition, the hammerhead turn is an aerobatic manoeuvre where the airplane enters a vertical climb from manoeuvring speed (or the recommended indicated airspeed for the aerobatic airplane involved). As the airplane slows, but before it encounters stall buffet, the pilot initiates the turn. For a left turn, the torque of the engine aids in making the turn. Application of left rudder is coordinated with the application of right aileron and forward movement of the control wheel (left rudder and left aileron used together causes the airplane to roll onto its back). When the airplane pivots to a nose-down position, back pressure is used to fly out of the resulting dive. Definitely it is best to avoid this manoeuvre in a "tight."

The airplane is usually at a dangerously low airspeed when the pilot arrives at the "tight." This precludes even thinking about performing the hammerhead manoeuvre. Even with plenty of airspeed, it would be stupid (as in not exhibiting common sense) to try the hammerhead.

The airplane used for mountain flying is probably not an aerobatic certified machine.

Wing Over

The wing over is more of a fun manoeuvre than an emergency escape manoeuvre. Usually the pilot pre-plans the wing over, allowing sufficient airspeed to transition from level flight to a climbing pitch attitude of about 40 degrees. During the increase in pitch, a coordinated bank is begun. The maximum pitch is reached after about a quarter turn (45 degrees of turn). At this point the back pressure is completely relaxed, but the bank continues to increase to 90 degrees. The bank is rolled out during the last quarter of the turn and back pressure is increased to arrest the descent. The airplane should arrive at the 180-degree turn point at the same altitude at which it began the manoeuvre.

Again, this is a manoeuvre that is intentionally performed for fun, rather than to escape during an emergency situation.

Steep Turn

The safest and perhaps the most commonly used method of course reversal is the steep turn. It is very similar to the box canyon turn.

The stall speed of an airplane increases as the square root of the wing load factor. In a 60-degree coordinated turn, regardless of airspeed, the airplane experiences a 2-g load factor. The square root of 2 is 1.41, so there is a 41 percent increase in stall speed.

Most pilots don't really care how to determine the radius of turn. By formula, the radius of a turn is equal to the velocity in true airspeed (knots) squared and then divided by a constant of 11.26 times the tangent of the bank angle in degrees.

The valid information this formula provides is the fact that the radius of turn can be shortened by either reducing the true airspeed, or by increasing the angle of bank. A combination of the two provides the greatest benefit.

The ratio of turn radius to an increase in airspeed at a constant bank varies as the square of the true airspeed. If the airplane doubles its speed, it will quadruple the distance travelled. So even if the airplane is going faster (twice as fast in this case), it still takes twice the amount of time to complete the turn around (four times further travelled).

What about using flaps during this steep turn? Definitely, use them as appropriate to the flight conditions. Flaps were invented to allow an airplane to increase its approach angle without an increase in airspeed. They work because lift and drag are directly proportional. If the lift is increased (by applying flaps to increase the camber of the wing), the drag is increased (and hence, no increase in airspeed).

For most airplanes the addition of flaps, up to half the total available, provides more lift than drag because the drag can be “subdued” with excess power.

At a high density altitude it may not be possible to use full flaps without intentionally losing altitude to maintain a safe airspeed. If a trade-off between altitude and airspeed cannot be made because of rapidly rising terrain, limit the use of the flaps to the extent that the airplane will maintain a constant altitude during the turn.

Remember too that flaps reduce the structural strength of the airplane. Many of the normal category airplanes are stressed for 3.8 gs (g = gravity unit). This is the limit-load factor that should not be exceeded. Okay, you say, what about the ultimate load factor, you know, that 50-percent safety factor built into the airplane? Shouldn't the airplane be capable of flying at 5.7 gs?

The correct response requires a definite and emphatically strong NO. For certification the airplane must be able to withstand the ultimate load factor for a period of fewer than 2 seconds without permanent deformation of the structure. More time than this at a load greater than the limit-load factor and the airplane may experience structural failure (that is, the wing breaks off).

Check the POH (pilots operating handbook) to determine the amount of reduction in structural strength with the application of flaps. The book may say: normal category 3.8 gs; flaps extended 2.2 gs (a 42 percent reduction).

Box Canyon Turn - Introduction

The box canyon turn varies from the steep turn in that it is either performed from level flight at such a slow airspeed that an unintentional stall is imminent, or some excess airspeed at the beginning of the manoeuvre allows the nose to be raised above the horizon prior to initiating the bank and the airspeed, during the turn, will be too slow to sustain level flight.

We have learned the airplane always stalls at the same critical angle of attack. When banking the airplane, the stall speed increases (remember? it increases as the square root of the wing load factor). Whenever the airplane is banked in a coordinated turn, it is balancing the centripetal force (horizontal lift component that causes the turn) and the centrifugal force (the force of the turn). The turn takes place because the centripetal force pulls the airplane towards the inside of the turn.

Without a compensating increase in the amount of total lift during a turn, the airplane will lose altitude. The total lift (lift) is divided between a vector force that sustains the weight of the airplane and its contents (weight). The portion of lift that is directed sideward (centripetal force) causes the turn. The centrifugal force acts towards the outside of the turn.

To maintain level flight while turning it is necessary to increase back pressure (more lift equals an increase in angle of attack). This increases the load factor and stall speed.

Some pilots get into trouble with the box canyon turn without realizing it because they have been "conditioned" to maintain level flight when performing steep turns.

Box Canyon Turn - Procedure from Cruise Flight

The first time a pilot has to perform a box canyon turn in a true life situation, he may feel like the lady who climbs on a stool to avoid a mouse scampering across the floor. A little scream to get the adrenaline flowing wouldn’t hurt either.

The box canyon turn could be described as a combination of the steep turn and wing over (when entered at or near cruise airspeed). The nose is raised above the horizon, but nowhere near the 40-degree attitude of the wing over. About five to 20 degrees is about right, depending on the airspeed.

This does two things for you. First it trades airspeed for altitude and second, it slows the airspeed for a smaller radius of turn.

At the same time, full power is added and full flaps (providing the airspeed is within the flap operating range) are applied while beginning the bank. The bank will be a minimum of 60 degrees and may approach 90 degrees.

To insure that the g-load factor is not exceeded during the steep bank it is necessary to relax the back pressure once the bank passes about 45 degrees. The back pressure is not increased again until the bank passes through about 45 degrees toward zero degrees during the rollout.

 Initiate the turn - the procedure requires coordination to accomplish all items at the same time:

Increase pitch attitude
Increase power
Begin a bank
Apply full flaps

At approximately 45 degrees of bank increasing toward 60-90 degrees:  

Relax back pressure from the control wheel

 Recovery - at approximately 45 degrees of bank, decreasing from 60-90 degrees:  

Increase back pressure on the control wheel to arrest any loss of altitude.
When the airplane is in a position that allows, reduce flaps to one half

Box Canyon Turn - Procedure from Climbing Flight

When operating near cruise airspeed the box canyon turn was described as a combination of the steep turn and wing over where the nose was raised above the horizon.

Hopefully, the airspeed is near the best rate-of-climb speed or best angle-of-climb speed. This is usually a critical situation because the airspeed will probably be slower than Vy or Vx due to the “short-arm” effect.

While applying full power and full flaps, a bank is established at a minimum of 60 degrees. Again the bank may approach 90 degrees.

Previously we stated that the back pressure was relaxed to insure that the g-load factor was not exceeded. This is not as much of a problem at low speed, but it still exists. At the slow speed the airplane will probably stall before it exceeds the structural limitations. The main reason for relaxing the back pressure now is so the airplane does not stall. The back pressure is not increased again until the bank passes through about 45 degrees toward zero degrees during the rollout.

 Initiate the turn - the procedure requires coordination to accomplish all items at the same time:  

Maintain pitch attitude initially
Increase power
Begin a bank
Apply full flaps

At approximately 30 degrees of bank, increasing toward 60-90 degrees:  

Relax back pressure from the control wheel
The pitch attitude will fall below the horizon

 Recovery - at approximately 30 degrees of bank, decreasing toward zero degrees:  

Increase back pressure on the control wheel
Reduce flaps to one half

Natural Horizon

The natural horizon is used to teach flying by outside visual reference. An instructor demonstrates a climb attitude at the best rate-of-climb airspeed. The student mimics this attitude. The airspeed indicator can be covered and the student, by noticing the pitch attitude in relation to the horizon (where the horizon intersects the side of the nose cowling), is able to fly at the best rate-of-climb airspeed within plus or minus one knot. Learning the “climb attitude” can provide for a very accurate climb speed, without looking at the airspeed indicator.  

The instructor also demonstrates where is the nose in relation to the horizon in level flight, where are the wings in relation to the horizon in level flight, and where is the nose in relation to the horizon in a steep turn (left and right turns).

This natural horizon is easy to use in the flatlands as a reference for basic attitude flying. In the mountains, the natural horizon may disappear. By visualizing a horizon, basic attitude flying can still be maintained. The base of the mountains, at least six to eight miles away, represents the natural horizon.

What if the airplane is closer than the six to eight miles? Visualization must be used. Perhaps the mountains at least six to eight miles in the distance are visible out the side window. Project the same horizon visually to the front of the airplane.


The box canyon turn is an emergency procedure. It is best to practice it with an experienced instructor prior to the time when it becomes necessary as a life-saving manoeuvre.

Without practice it is very easy to get into an accelerated stall condition that will exacerbate the original situation.


You must exercise caution in using full flaps during the practice of the box canyon turn and for drainage searches because of the possibility of the flaps failing in the extended position. 

For practice you may want to restrict the use of flaps because of the real possibility of the flaps failing to retract. It is possible to demonstrate and learn the box canyon turn without full flaps where the same technique, using full flaps, is applicable to a real "tight" or emergency condition.