Stall Recognition and Recovery

What is a Stall?

Most people think that a stall in an airplane is just like a stall in a car. When a car stalls it quits working. This is not the case in an airplane.

Most people have put their hand out the window of a car and played airplane. They notice that if they increase the angle of the hand too much that it is pushed backwards and quits flying. They also know that if they reduce the angle of the hand that it starts to fly again. If the car slows down the hands ability to fly stops below a certain speed.

Airplanes behave in much the same way. It requires a certain amount of air to flow over the wing before the airplane will begin to fly. This speed is called the stall speed, because, under normal circumstances the plane will not fly below that speed.

Angle of Attack

The angle of attack is the angle of the relative wind or motion of the entire airplane relative to the line between the front of the wing and the back of the wing. As the angle increases more lift usually occurs. For each wing there is a specific angle at which the air flowing over the wing begins to tumble. Most aircraft are designed so that the wing is shaped differently near the body of the aircraft than near the tip of the wing. The angle at which the wing stalls near the body of the plane is slightly lower than the rest of the wing. As the air begins to tumble the pilot can feel vibration in the plane and its controls. If he recognizes this and reduces the angle of attack then a stall is avoided.

When aircraft are designed, The weight and balance envelope assures that the nose of the aircraft will always be heavier than the tail. When the aircraft stalls the weight of the nose causes it to fall reducing the angle of attack forcing the airplane to recover from the stall all by itself. If the pilot allows the plane to recover then the plane will fly itself out of the stall. This assumes that the airspeed is sufficient for the airplane to fly. If you are landing the airplane the ideal is for the airplane to stop flying (stall) just as the wheels touch the ground. This keeps the tires from wearing out as fast.

Slow Flight

Slow flight is the art of flying the airplane just above stall speed. We practice slow flight to get used to the signs of the impending stall, but the real value of slow flight occurs when we begin to bank the aircraft. As the bank increases, centifugal force causes the aircraft to weigh more and therefore the angle of attack increases. As we decrease the angle of attack the speed of the aircraft increases,but we are still in slow flight, just above the stall. Most aircraft stall at about 60-70 mph, but in a steep 45-60 degree turn the stall speed increases to 85-90 mph. This is the normal approach speed for most aircraft. We find the actual number by practicing slow flight at that steep angle.

Once we learn this speed we will find the speed we never want to approach when turning to land that aircraft. Most accidents in the pattern occur because the pilot makes a steep turn at his normal approach speed and the aircraft stalls. If he recognizes the impending stall he survives, if not he dies. Simple to avoid, deadly if ignored.

TYPES OF STALLS

Why practice stalls in the first place? If you know what it feels like when you stall an aircraft, it is easier to recognize when you are getting close so that you can take corrective action.

Stalls 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 to avoid entering a non-recoverable flat spin. 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.

STALL RECOVERY

The key factor in recovering from a stall is 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. 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 inadvertenly causing the angle of attack to again be exceeded. 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

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. Most aircraft will fly themselves out of a spin, but neutralizing the ailerons and elevator and applying opposite rudder usually expedite the recovery.

WEIGHT AND BALANCE

As seen earlier, the weight and balance envelope is designed to keep the nose heavier than the tail. Minor weight or balance changes beyond this envelope can affect an aircraft’s handling 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.

PRIMARY CAUSE

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.

TYPES OF SPINS

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. Loading the aircraft beyond the aft limit usually causes the flat spin.

SPIN RECOVERY

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.

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.

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.

DEPARTURE STALL

(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.

ENGINE FAILURE IN A CLIMB FOLLOWED BY A 180-DEGREE GLIDING TURN

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.

(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

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.

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.

STALLS DURING GO-AROUNDS

(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.

ELEVATOR TRIM STALL

(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.

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