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There are several ways to recognize that a stall is impending before it actually occurs. When one or more of these indicators is noted, initiation of a recovery should be instinctive (unless a full stall is being practiced intentionally from an altitude that allows recovery above 1,500 feet above ground level (AGL) for single-engine airplanes and 3,000 feet AGL for multi-engine airplanes). One indication of a stall is a mushy feeling in the flight controls and less control effect as the aircraft’s speed is reduced. This reduction in control effectiveness is attributed in part to reduced airflow over the flight control surfaces. In fixed-pitch propeller airplanes, a loss of revolutions per minute (RPM) may be evident when approaching a stall in power-on conditions. For both airplanes and gliders, a reduction in the sound of air flowing along the fuselage is usually evident. Just before the stall occurs, buffeting, uncontrollable pitching, or vibrations may begin. Many aircraft are equipped with stall warning devices that will alert the pilot when the airflow over the wing(s) approaches a point that will not allow lift to be sustained. Finally, kinesthesia (the sensing of changes in direction or speed of motion), when properly learned and developed, will warn the pilot of a decrease in speed or the beginning of a "mushing" of the aircraft. Because of the ability of the body to easily be fooled, this kinesthesia should be cross checked with other sources or instruments. These preliminary indications serve as a warning to the pilot to increase airspeed by adding power, and/or lowering the nose, and/or decreasing the angle of bank.
TYPES OF STALLSStalls can be practiced both with and without power. Stalls should be practiced to become familiar with the aircraft’s particular stall characteristics without putting the aircraft into a potentially dangerous condition. In multi-engine airplanes, single-engine stalls must be avoided. A description of some different types of stalls follow:
a. Power-off stalls (also known as approach-to-landing stalls) are practiced to simulate normal approach-to-landing conditions and configuration. Many stall/spin accidents have occurred in these power-off situations, such as crossed control turns from base leg to final approach (resulting in a skidding or slipping turn); attempting to recover from a high sink rate on final approach by using only an increased pitch attitude; and improper airspeed control on final approach or in other segments of the traffic pattern.
b. Power-on stalls (also known as departure stalls) are practiced to simulate takeoff and climb-out conditions and configuration. Many stall/spin accidents have occurred during these phases of flight, particularly during go-arounds. A causal factor in such accidents has been the pilot’s failure to maintain positive control due to a nose-high trim setting or premature flap retraction. Failure to maintain positive control during short field takeoffs has also been an accident causal factor.
c. Accelerated stalls can occur at higher-than-normal airspeeds due to abrupt and/or excessive control applications. These stalls may occur in steep turns, pull ups, or other abrupt changes in flight path. Accelerated stalls usually are more severe than unaccelerated stalls and are often unexpected because they occur at higher-than-normal airspeeds.
The key factor in recovering from a stall is regaining positive control of the aircraft by reducing the angle of attack. At the first indication of a stall, the aircraft angle of attack must be decreased to allow the wings to regain lift. Every aircraft in upright flight may require a different amount of forward pressure to regain lift. It should be noted that too much forward pressure can hinder recovery by imposing a negative load on the wing. The next step in recovering from a stall is to smoothly apply maximum allowable power (if applicable) to increase the airspeed and to minimize the loss of altitude. Certain high performance airplanes may require only an increase in thrust and relaxation of the back pressure on the yoke to effect recovery. As airspeed increases and the recovery is completed, power should be adjusted to return the airplane to the desired flight condition. Straight and level flight should be established with full coordinated use of the controls. The airspeed indicator or tachometer, if installed, should never be allowed to reach their high-speed red lines at any time during a practice stall.
SECONDARY STALLS
If recovery from a stall is not made properly, a secondary stall or a spin may
result. A secondary stall is caused by attempting to hasten the completion of a
stall recovery before the aircraft has regained sufficient flying speed. When
this stall occurs, the back elevator pressure should again be released just as
in a normal stall recovery. When sufficient airspeed has been regained, the
aircraft can then be returned to straight-and-level flight.
SPINS WEIGHT AND BALANCE PRIMARY CAUSE a. An incipient spin is that portion of a spin from
the time the airplane stalls and rotation starts, until the spin
becomes fully developed. Incipient spins that are not allowed to develop into
a steady state spin are commonly used as an introduction to spin training and
recovery techniques. b. A fully developed spin occurs when the aircraft
angular rotation rates, airspeed, and vertical speed are stabilized
from turn-to-turn in a flight path that is close to vertical. c. A flat spin is characterized by a near level pitch
and roll attitude with the spin axis near the CG of the airplane. Recovery
from a flat spin may be extremely difficult and, in some cases, impossible. SPIN RECOVERY If the spin does not stop after all of the above efforts have been attempted,
application of full power may be needed to provide sufficient air flow across
the rudder to stop the spin. If all else fails you should put your head
between your legs and kiss your touche goodbye.
A spin in a small airplane or glider is a controlled or uncontrolled maneuver in
which the glider or airplane descends in a helical path while flying at an angle
of attack greater than the angle of maximum lift. Spins result from aggravated
stalls in either a slip or a skid. If a stall does not occur, a spin cannot
occur. In a stall, one wing will often drop before the other and the nose will
yaw in the direction of the low wing.
Minor weight or balance changes can affect an aircraft’s spin characteristics.
For example, the addition of a suitcase in the aft baggage compartment will
affect the weight and balance of the aircraft. An aircraft that may be difficult
to spin intentionally in the utility category (restricted aft CG and reduced
weight) could have less resistance to spin entry in the normal category (less
restricted aft CG and increased weight) due to its ability to generate a higher
angle of attack and increased load factor. Furthermore, an aircraft that is
approved for spins in the utility category, but loaded in the normal category,
may not recover from a spin that is allowed to progress beyond one turn.
The primary cause of an inadvertent spin is exceeding the critical angle of
attack for a given stall speed while executing a turn with excessive or
insufficient rudder and, to a lesser extent, aileron. In an uncoordinated
maneuver, the pitot/static instruments, especially the altimeter and airspeed
indicator, are unreliable due to the uneven distribution of air pressure over
the fuselage. The pilot may not be aware that a critical angle of attack has
been exceeded until the stall warning device activates. If a stall recovery is
not promptly initiated, the airplane is more likely to enter an inadvertent
spin. The spin that occurs from cross controlling an aircraft usually results in
rotation in the direction of the rudder being applied, regardless of which wing
tip is raised. In a skidding turn, where both aileron and rudder are applied in
the same direction, rotation will be in the direction the controls are applied.
However, in a slipping turn, where opposite aileron is held against the rudder,
the resultant spin will usually occur in the direction opposite the aileron that
is being applied.
Before flying any aircraft, in which spins are to be conducted, the pilot should
be familiar with the operating characteristics and standard operating
procedures, including spin recovery techniques, specified in the approved AFM or
POH. The first step in recovering from an upright spin is to close the throttle
completely to eliminate power and minimize the loss of altitude. If the
particular aircraft spin recovery techniques are not known, the next step is to
neutralize the ailerons, determine the direction of the turn, and apply full
opposite rudder. When the rotation slows, briskly move the elevator control
forward to approximately the neutral position. Some aircraft require merely a
relaxation of back pressure; others require full forward elevator control
pressure. Forward movement of the elevator control will decrease the angle of
attack. Once the stall is broken, the spinning will stop. Neutralize the rudder
when the spinning stops to avoid entering a spin in the opposite direction. When
the rudder is neutralized, gradually apply enough aft elevator pressure to
return to level flight. Too much or abrupt aft elevator pressure and/or
application of rudder and ailerons during the recovery can result in a secondary
stall and possibly another spin. If the spin is being performed in an airplane,
the engine will sometimes stop developing power due to centrifugal force acting
on the fuel in the airplane’s tanks causing fuel interruption. It is,
therefore, recommended to assume that power is not available when practicing
spin recovery. As a rough estimate, an altitude loss of approximately 500 feet
per each 3-second turn can be expected in most small aircraft in which spins are
authorized. Greater losses can be expected at higher density altitudes.
STALL AVOIDANCE PRACTICE AT SLOW AIRSPEEDS (1) Assign a heading and an altitude. Reduce power and slow
to an airspeed just above the stall speed, using trim as necessary. (2) Maintain heading and altitude with the stall warning
device activated. (3) Demonstrate the effect of elevator trim (use neutral and
full nose-up settings) and rudder trim, if available. (4) Note the left turning tendency and rudder effectiveness
for lateral/directional control. (5) Emphasize how right rudder pressure is necessary to
center the ball indicator and maintain heading. (6) Release the rudder and observe the left yaw. (7) Adverse yaw demonstration. While at a low airspeed,
enter left and right turns without using rudder pedals. (8) Practice turns, climbs, and descents at low airspeeds. (9) Demonstrate the proper flap extension and retraction
procedures while in level flight to avoid a stall at low airspeeds. Note the
change in stall speeds with flaps extended and retracted. (10) Realistic distractions at low airspeeds. With a safety
pilot or instructor aboard pick something up off of the floor while flying at a
low airspeed. Divide your attention between the task and flying the aircraft to
maintain control and avoid a stall. The following distractions can be used: (i) Drop a pencil and then pick it up. Determine
a heading to an airport using a chart. (ii) Reset the clock to Universal
Coordinated Time. (iii) Get something from the back seat. (iv) Read the outside air temperature. (v) Call the Flight Service Station (FSS)
for weather information. (vi) Compute true airspeed with a flight
computer. (vii) Identify terrain or objects on the
ground. (viii) Identify a field suitable for a
forced landing. (ix) Climb 200 feet and maintain altitude,
then descend 200 feet and maintain altitude. (x) Reverse course after a series of
S-turns. (11) Flight at low airspeeds with the airspeed indicator
covered. Use various flap settings and distractions. (1) At a safe altitude, attempt coordinated power-on
(departure) stalls straight ahead and in turns. Emphasize how these stalls could
occur during takeoff. (2) Demonstrate a power-on (departure) stall and have the
safety pilot distract you just before the stall occurs. Explain any effects the
distraction may have had on the stall or recovery. (1) Set up best rate of climb (Vy) (2) Reduce power smoothly to idle as the airplane passes
through a cardinal altitude. (3) Lower the nose to maintain the best glide speed and
make a 180-degree turn at the best glide speed. (4) Note the altitude loss and emphasize how rapidly
airspeed decreases following a power failure in a climb attitude. (5) Perform this at least 3000 feet AGL CROSS CONTROLLED STALLS IN GLIDING TURNS Show the effect of improper control technique and emphasize
the importance of correct control usage. Explain the ball indicator position in
each turn and the aircraft behavior in each of the stalls. POWER-OFF (APPROACH-TO-LANDING) STALLS
(1) Perform a full -flap, gear extended, power-off stall
with the correct recovery and cleanup procedures. Note the loss of altitude. (2) Repeat this procedure and have the safety pilot
distract you during the stall and recovery and note the effect of the
distraction. Show how errors in flap retraction procedure can cause a
secondary stall. (1) Perform a full-flap, gear extended, power-off stall,
then recover and attempt to climb with flaps extended. If a higher than normal
climb pitch attitude is held, a secondary stall will occur. (In some
airplanes, a stall will occur if a normal climb pitch attitude is held.) (2) Perform a full-flap, gear extended, power-off stall,
then recover and retract the flaps rapidly as a higher than normal climb pitch
attitude is held. A secondary stall or settling with a loss of altitude may
result. (1) Place the airplane
in a landing approach configuration, in a trimmed descent. (2)After the descent is
established, initiate a go-around by adding full power, holding only light
elevator and right rudder pressure. (3) Allow the nose to pitch up and torque to swerve the
airplane left. At the first indication of a stall, recover to a normal climbing
pitch attitude. (4) Emphasize the importance of correct attitude control,
application of control pressures, and proper trim during go-arounds.
This demonstration will show how much altitude the airplane loses
following a power failure after takeoff and during a 180-degree turn back to the
runway and why returning to the airport after losing an engine is not a
recommended procedure. This can be performed using either a medium or steep bank
in the 180-degree turn, but emphasis should be given to stall avoidance.
Perform stalls in gliding turns to simulate turns from base to final. Perform
the stalls from a properly coordinated turn, a slipping turn, and a skidding
turn. Explain the difference between slipping and skidding turns.
STALLS DURING GO-AROUNDS