No one should need
the box canyon turn under normal circumstances. If you need this
have violated the laws of mountain flying.
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.
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.
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
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.
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.
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.
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."
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
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
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
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
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
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."
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.
airplane used for mountain flying is probably not an aerobatic certified
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
safest and perhaps the most commonly used method of course reversal is the
steep turn. It is very similar to the box canyon turn.
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.
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.
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
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).
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).
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
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?
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).
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 -
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.
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.
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.
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
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
Increase pitch attitude
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
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
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
At approximately 30 degrees of bank, increasing
toward 60-90 degrees:
Recovery - at approximately 30 degrees of bank,
decreasing toward zero degrees:
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
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.