Chapter 4: Maintaining Aircraft Control
A pilot's fundamental responsibility is to prevent a loss of control (LOC), which is the leading cause of fatal general aviation accidents. Maneuvering is the most common phase of flight for general aviation loss-of-control accidents to occur.
Pilots must recognize situations that increase the risk of loss of control, such as uncoordinated flight, equipment malfunctions, pilot complacency, distraction, turbulence, poor risk management, intentional disregard, and recklessness.
Upset, Coordinated Flight, and Angle of Attack
An airplane upset is an event that unintentionally exceeds the parameters normally experienced in flight or training.
Upset Prevention and Recovery Training (UPRT) includes slow flight, stalls, spins, and unusual attitudes. This training includes both prevention and proper recovery techniques.
An airplane is in coordinated flight when the airplane's nose is yawed directly into the relative wind and the inclinometer (the "ball") is centered in the slip/skid indicator. If uncoordinated, a correction should be made by applying rudder pressure on the side toward which one feels a leaning sensation (often referred to in flight training as "step on the ball.")
Angle of Attack (AOA) is the angle at which the chord of the wing meets the relative wind. At low angles of attack, the airflow over the top of the wing flows smoothly and produces lift with a relatively small amount of drag. The chord is a straight line from the leading edge to the trailing edge of the wing.
As the AOA increases, lift as well as drag increases. Above a wing's critical AOA, the flow of air separates from the upper surface. This reduces lift and increases drag, creating an aerodynamic stall. Angle of attack should be reduced. Loss of control in the stall is possible.
A stall is the result of exceeding the critical AOA. A stall is not caused by insufficient airspeed. "Stalling speed" is a common reference to 1G flight at a particular aircraft weight and configuration. However, stalling speed varies with changes in load factor, gross weight, configuration, and center of gravity (CG).
It is possible to stall the wing at any airspeed, at any flight attitude, and at any power setting.
In a 60° banked turn, the load factor is 2Gs. This increases the airplane's stalling speed by 40%, compared to straight-and-level flight at the same airspeed.
Slow flight occurs when the airplane's angle of attack is just under the AOA which will cause an aerodynamic buffet or a warning from a stall warning device.
Because the airplane is flown at higher angles of attack, and thus reduced speeds in the takeoff/departure and approach/ landing phases of flight, learning to fly at reduced airspeeds is essential. In these phases of flight, the airplane's close proximity to the ground would make loss of control catastrophic.
The objective of maneuvering in slow flight is to understand the flight characteristics and how the airplane's flight controls feel near its aerodynamic buffet or stall-warning. During slow flight, the pilot will experience degraded response to control inputs and difficulty maintaining altitude.
In flight training and testing, pilots should be able to slow to, maneuver at, and recover from an airspeed at which the airplane is still capable of maintaining controlled flight without activating the stall warning. They also should be able to perform slow flight in configurations appropriate to takeoffs, climbs, descents, approaches to landing, and go-arounds.
Flight at lower airspeeds aids the pilot in learning that as airspeed decreases, control effectiveness decreases. The reduced airflow over the control surfaces results in larger control movements being required to create the same response the pilot would expect in normal flight. This is due to less airflow over the control surfaces.
Behind the Power Curve
When flying above minimum drag speed (L/D max), even a small increase in power will increase the speed of the airplane. When flying at speeds below L/D max, larger inputs in power, or reducing angle of attack, will be required for the airplane to be able to accelerate.
Flying at speeds below L/D max is commonly referred to as "flying on the back side of the power curve" or "behind the curve."
When flying below L/D max, pitch is a more effective control of airspeed, and power is an effective control of the altitude profile.
Below L/D max, pilots can expect "speed instability." For example, if the airplane is disturbed by turbulence and the airspeed decreases, the airspeed will continue to decay without appropriate pilot action, such as reducing angle of attack and/or adding power.
Maneuvering in Slow Flight
Slow flight should be practiced in straight-and-level flight. Pilots should also practice straight-ahead climbs, climbing medium-banked turns, straight-ahead power-off gliding descents, and descending turns. This is to represent the takeoff and landing phases of flight.
Slowing the airplane smoothly and promptly from cruising to approach speeds should be done without changes in altitude or heading. Configuration changes include adding flaps and extending the landing gear (if retractible).
Slow flight maneuvers should be completed no lower than 1,500 feet AGL.
Gradually reduce thrust from cruise power and adjust the pitch to allow the airspeed to decrease while maintaining altitude. As the speed approaches the target slow flight speed (just above stall warning), additional power will be required to maintain altitude.
In propeller-driven airplanes, torque, slipstream effect, and P-factor may produce a strong left yaw, which requires right rudder input to maintain coordinated flight.
The pilot should practice turns to determine the airplane's controllability characteristics in slow flight. In turns, it will be necessary to increase power to maintain altitude.
The pilot should also practice climbs and descents by adjusting the power when stabilized in straight-and-level slow flight.
To exit the slow flight maneuver, follow the same procedure as for recovery from a stall: apply forward control pressure to reduce the AOA, maintain coordinated flight and level the wings, and apply power as necessary to return to the desired flightpath. As airspeed increases, clean up the airplane by retracting flaps and landing gear.
Common errors in the performance of slow flight are:
A stall is an aerodynamic condition which occurs when smooth airflow over the airplane's wings is disrupted, resulting in loss of lift.
A stall occurs when the angle of attack exceeds the wing's critical AOA. It is possible to exceed the critical AOA at any airspeed, at any attitude, and at any power setting.
Performing intentional stalls will familiarize the pilot with the conditions that result in a stall, assist in recognition of an impending stall, and develop the proper corrective response.
An impending stall occurs when the angle of attack causes a stall warning, but the wing's chord has not yet reached the critical AOA. Indications of an impending stall can include buffeting and an audible stall warning device, such as a stall horn. Advanced aircraft may have a stick shaker installed.
A full stall occurs when the critical angle of attack is exceeded. A full stall typically results in an uncommanded nose-down pitch, along with an uncommanded rolling motion. Advanced aircraft may have a stick pusher, which will activate.
Some loss of altitude is expected during stall recovery.
A pilot must recognize the flight conditions that are conducive to stalls and know how to apply the necessary corrective action. While audible stall-warning devices are common on training aircraft, some vintage aircraft are certified to provide a stall warning through the inherent aerodynamic qualities of the airplane.
As the airplane approaches a stall, the pilot will feel control pressures change. Larger control movements will be required for the desired airplane response. The airplane's reaction time to control movement increases. Just before the stall, buffeting, uncommanded rolling, or vibrations may begin to occur.
As airspeed decreases, the pilot should notice a change in sound made by the air flowing along the airplane structure.
Kinesthesia is the physical sensation of changes in direction or speed. It can be an important indicator to the trained and experienced pilot in visual flight, warning the pilot of an impending stall.
Airplanes can be equipped with angle of attack indicators that can provide a visual indication of the airplane's proximity to the critical AOA. Pilots are encouraged to conduct in-flight training to see the indications throughout various maneuvers.
Engineering design variations make it impossible to specifically describe the stall characteristics for all airplanes. The pilot should know the stall characteristics of the airplane being flown and the manufacturer's recommended recovery procedures.
Most training airplanes are designed so that the wings stall progressively outward from the wing roots to the wingtips.
Some wings have an amount of twist, known as washout, so that the outboard portion of the wings having a slightly lower angle of attack than the wing roots. The wingtips thus have a smaller angle of attack during flight than the wing roots. In a stall, the wing roots will stall first, which permits the ailerons to have a degree of control effectiveness.
The most important action to an impending stall or a full stall is to reduce the angle of attack.
Adding power and attempting to maintaining altitude, without first reducing angle of attack, can result in a loss of control.
Pilots should always follow the aircraft-specific manufacturer's recommended stall-recovery procedures.
In a single-engine training airplane, the order of stall recovery steps is as follows:
Stall accidents usually result from an inadvertent stall at a low altitude, with the recovery not completed prior to ground contact. Practice in both power-on and power-off stalls is important because it simulates stall conditions that could occur during normal flight maneuvers.
An impending stall occurs when the airplane is approaching, but does not exceed the critical AOA. The purpose of practicing impending stalls is to learn to retain or regain full control of the airplane immediately upon recognizing that it is nearing a stall, or that a stall is likely to occur if the pilot does not take appropriate action.
Instead of allowing the airplane to reach the critical AOA, the pilot must immediately reduce AOA once the stall warning device goes off, if installed, or recognizes other cues such as buffeting.
The pilot will have recovered once the airplane has returned to the desired flightpath with sufficient airspeed and adequate flight control effectiveness and no stall warning.
Full Stalls, Power-Off
To set up the entry for a straight-ahead power-off stall, airplanes equipped with flaps or retractable landing gear should be in the landing configuration. Hold the airplane at a constant altitude in level flight until the airspeed decelerates to normal approach speed. The airplane should then be smoothly pitched down to a normal approach attitude to maintain that airspeed.
When the approach attitude and airspeed have stabilized, the pilot should smoothly raise the airplane's nose to an attitude that induces a stall. Directional control should be maintained and wings held level by coordinated use of the ailerons and rudder. Pitch attitude is maintained with the elevator until the stall occurs. The stall is recognized by the full-stall cues.
Recovery from the stall is accomplished by reducing the AOA, applying as much nose-down control input as required to eliminate the stall warning, leveling the wings, maintaining coordinated flight, and then applying power as needed.
If simulating an inadvertent stall on approach to landing, the pilot should initiate a go-around by establishing a positive rate of climb. Flaps and landing gear should be retracted as necessary.
Recovery from power-off stalls should also be practiced from shallow banked turns to simulate an inadvertent stall during a turn from base leg to final approach. If the airplane is allowed to develop a slip, the outer wing may stall first and move downward abruptly. The recovery procedure is the same, regardless of whether one wing rolls off first. The pilot must apply as much nose-down control input as necessary to eliminate the stall warning, level the wings with ailerons, coordinate with rudder, and add power as needed.
Full Stalls, Power-On
Power-on stall (also known as departure stall) recoveries are practiced from straight climbs and climbing turns. These help the pilot recognize the potential for an accidental stall during takeoff, go around, climb, or when trying to clear an obstacle.
Power for practicing the takeoff stall recovery should be maximum power, although for some airplanes it may be reduced to a setting that will prevent an excessively high pitch attitude.
Establish the airplane in the takeoff or climb configuration. Set takeoff power or the recommended climb power while establishing a climb attitude. The purpose of reducing the airspeed to lift-off airspeed before the throttle is advanced to the recommended setting is to avoid an excessively steep nose-up attitude for a long period before the airplane stalls.
After establishing the climb attitude, smoothly raise the nose to increase the AOA, and hold that attitude until the full stall occurs.
The pilot must promptly recognize when the stall has occurred, immediately reduce the AOA, and apply the nose-down control input necessary to eliminate the stall warning, level the wings with ailerons, coordinate with rudder, and confirm the proper power setting. Finally, return the airplane to the desired flightpath.
For pilot certification, the secondary stall is a demonstration-only maneuver. Flight instructor applicants may be required to perform it on a practical test.
A secondary stall occurs after recovery from a preceding stall, typically due to abrupt control inputs or attempting to return to the desired flightpath too quickly, which exceeds the critical AOA for a second time. .
When a secondary stall occurs, the pilot should again perform the stall recovery procedures.
An airplane can stall at a higher indicated airspeed than the +1G stalling speed when the airplane is subject to an acceleration greater than +1G, such as when turning, pulling up, or other abrupt changes in flightpath.
Stalls encountered any time the G-load exceeds +1G are called accelerated maneuver stalls. Only commercial pilot and flight instructor applicants may be required to perform or demonstrate accelerated stalls on a practical test. An accelerated stall is typically demonstrated during steep turns.
The objectives of demonstrating an accelerated stall are to determine the stall characteristics of the airplane, experience stalls at speeds greater than the +1G stall speed, and develop the ability to instinctively recover at the onset of such stalls.
The accelerated stall would most frequently occur inadvertently during improperly executed turns, stall and spin recoveries, pullouts from steep dives, or when overshooting a base to final turn.
Accelerated stalls should be performed with a bank of approximately 45°, and a speed no greater than the airplane manufacturer's recommended airspeed or the specified design maneuvering speed (Va). This is the maximum speed at which the maximum positive design load limit can be imposed either by gusts or full one-sided deflection with one control surface without causing structural damage.
Performing accelerated stalls at or below Va allows the airplane to reach the critical angle of attack, which unloads the wing before it reaches the load limit. At speeds above Va, the wing can reach the design load limit at an AOA less than the critical AOA. This means it is possible to damage the airplane before reaching the critical AOA and an accelerated stall.
The aerodynamic effects of the uncoordinated, cross-control stall can surprise the unwary pilot because it can occur with very little warning and can be deadly if it occurs close to the ground. The nose may pitch down, the bank angle may suddenly change, and the airplane may continue to roll to an inverted position, which is usually the beginning of a spin.
The objective of the cross-control stall demonstration is to show the effects of uncoordinated flight on stall behavior and to emphasize the importance of maintaining coordinated flight while making turns.
This is a demonstration-only maneuver. Only flight instructor applicants may be required to perform it on a practical test.
A cross-control stall occurs when the critical angle of attack is exceeded with aileron pressure applied in one direction and rudder pressure in the opposite direction, causing uncoordinated flight.
A skidding cross-control stall is most likely to occur in the traffic pattern during a poorly planned and executed base-to-final approach turn in which the airplane overshoots the runway centerline and the pilot attempts to correct back to centerline by increasing the bank angle, increasing back elevator pressure, and applying rudder in the direction of the turn ("inside" or "bottom" rudder). An unwanted increase in bank angle may result, as well as the nose of the airplane slicing downward through the horizon. If the pilot pulls back on the elevator control, the AOA could become critical.
At the relatively low altitude of a base-to-final approach turn, a pilot should be reluctant to use angles of bank beyond 30 degrees to correct back to runway centerline. When overshooting the runway centerline on final approach, the safest action is to perform a go-around.
To perform the stall, establish gliding attitude and airspeed. Roll into a medium-banked turn to simulate a final approach turn that overshoots the centerline of the runway. Apply excessive rudder pressure in the direction of the turn. Hold the bank constant by applying opposite aileron pressure. Increase back elevator pressure to keep the nose from lowering. All of these control pressures should be increased until the airplane stalls.
Recover by applying nose-down elevator pressure to reduce the AOA until the stall warning has been eliminated, remove the excessive rudder input and level the wings, and apply power as needed to return to the desired flightpath.
Elevator Trim Stall
The elevator trim stall demonstration shows what can happen when the pilot applies full power for a go-around without maintaining positive control of the airplane. This situation may occur during a go-around procedure from a normal landing approach or a simulated, forced-landing approach, or immediately after a takeoff, with the trim set for a normal landing approach glide at idle power.
This is a demonstration-only maneuver. Only flight instructor applicants may be required to perform it on a practical test.
The objective of the demonstration is to show the importance of making smooth power applications, overcoming strong trim forces, maintaining positive control of the airplane to hold safe flight attitudes, and using proper and timely trim techniques.
For demonstration, the pilot should trim the airplane nose-up for the normal landing approach glide. The throttle is then advanced smoothly to maximum allowable power, just as it would be adjusted to perform a go-around.
The combined effects of increased propwash over the tail and elevator trim tend to make the nose rise sharply and turn to the left. Pitch attitude increases above the normal climbing attitude.
When it is apparent the airplane is approaching a stall, the pilot must apply sufficient forward elevator pressure to reduce the AOA and eliminate the stall warning before returning the airplane to the normal climbing attitude. Adjust trim to relieve control pressures. Complete the normal go-around procedures and return to the desired flightpath.
Commercial Pilot & Flight Instructor Test Questions
Common mistakes made by student pilots while first performing intentional stalls are premature recovery, excessive back-elevator pressure, and excessive airspeed building during recovery.
Which is the correct symbol for the minimum steady flight speed at which an airplane is controllable? Vs.
— Vs1 and Vs0 are included as distractors. They denote Vs in specific aircraft configurations.
Which is a correct spin recovery technique? Reduce power to idle, apply opposite rudder and forward elevator control.
Which stall must be performed during a flight instructor (airplane) practical test? Power-on or power-off.
— Imminent stall is not a stall. Accelerated stalls are not required on the flight test.
The objective of a cross-control stall demonstration is to show the effect of improper control technique and emphasize the importance of coordinated control when making turns.
Two distinct flight situations should be covered when teaching slow flight. The are the establishment and maintenance of airspeeds appropriate for landing approaches, and flight at reduced airspeds.
The primary purpose of practicing operations at reduced airspeeds is to enable students to develop proficiency in their sense of feel and their ability to use the controls properly at various speeds.
If inadequate right rudder is used during a climbing right turn, what may occur if the aircraft stalls? A spin to the left.
Secondary stalls result from abrupt control movement.