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The pilot should understand that when flying below the minimum drag speed (L/D$_{MAX}$), the aircraft exhibits a characteristic known as “speed instability.” If the aircraft is disturbed by even the slightest turbulence, the airspeed decreases. As airspeed decreases, the total drag increases resulting in a further loss in airspeed. Unless more power is applied and/or the nose is lowered, the speed continues to decay to a stall. This is an extremely important factor in the performance of slow flight. The pilot must understand that, at speeds less than minimum drag speed, the airspeed is unstable and will continue to decay if allowed to do so. 

It should also be noted that the amount of power to remain level at minimum controlled airspeed is greater than that required at the minimum drag speed which is also the best glide ratio speed and the best rate of climb speed. 

When the attitude, airspeed, and power have been stabilized in straight-and-level flight, turns should be practiced to determine the aircraft’s controllability characteristics at this minimum speed. During the turns, power and pitch attitude may need to be increased to maintain the airspeed and altitude. The objective is to acquaint the pilot with the lack of maneuverability at minimum controlled airspeed, the danger of incipient stalls, and the tendency of the aircraft to stall as the bank is increased. A stall may also occur as a result of turbulence, or abrupt or rough control movements when flying at this critical airspeed. 

Once flight at minimum controllable airspeed is set up properly for level flight, a descent or climb at minimum controllable airspeed can be established by adjusting the power as necessary to establish the desired rate of descent or climb. 

Common errors in the performance of slow fl ight are: 

• Failure to adequately clear the area. 

• Inadequate forward pressure as power is reduced, resulting in altitude loss. 

• Excessive forward pressure as power is reduced, resulting in a climb, followed by a rapid reduction in airspeed and “mushing.” 

• Inadequate compensation for unanticipated roll during turns. 

• Fixation on the airspeed indicator. 

• Inadequate power management. 

• Inability to adequately divide attention between aircraft control and orientation. 

##  Stalls 

A stall occurs when the smooth airflow over the aircraft’s wing root is disrupted and the lift degenerates rapidly. This is caused when the wing root exceeds its critical angle of attack. This can occur at any airspeed in any attitude with any power setting. 

The practice of stall recovery and the development of awareness of stalls are of primary importance in pilot training. The objectives in performing intentional stalls are to familiarize the pilot with the conditions that produce stalls, to assist in recognizing an approaching stall, and to develop the habit of taking prompt preventive or corrective action. 

Pilots must recognize the flight conditions that are conducive to stalls and know how to apply the necessary corrective action. They should learn to recognize an approaching stall by sight, sound, and feel. The following cues may be useful in recognizing the approaching stall: 

• Positioning the control bar toward the front tube 

• Detecting a stall condition by visually noting the attitude of the aircraft for the power setting 

