characterized by a relatively weak tendency of the aircraft to  maintain the trim speed. In fact, it is likely the aircraft exhibits  no inherent tendency to maintain the trim speed in this area.  For this reason, the pilot must give particular attention to  precise control of airspeed when operating in the slow-speed  phases of the region of reversed command. Operation in the region of reversed command does not imply  that great control difficulty and dangerous conditions exist.  However, it does amplify errors of basic flying technique— making proper flying technique and precise control of the  aircraft very important. The characteristics of flight in the region of normal command  are illustrated at point A on the curve in  Figure 4-11 . If  the aircraft is established in steady, level flight at point A,  lift is equal to weight, and the power available is set equal  to the power required. If the airspeed is increased with no  changes to the power setting, a power deficiency exists.  The aircraft has a natural tendency to return to the initial  speed to balance power and drag. If the airspeed is reduced  with no changes to the power setting, an excess of power  exists. The aircraft has a natural tendency to speed up to  regain the balance between power and drag. Keeping the  aircraft in proper trim enhances this natural tendency. The  static longitudinal stability of the aircraft tends to return the  aircraft to the original trimmed condition. An aircraft flying in steady, level flight at point C is in  equilibrium.  [Figure 4-11] If the speed were increased  or decreased slightly, the aircraft would tend to remain at  that speed. This is because the curve is relatively flat and  a slight change in speed does not produce any significant  excess or deficiency in power. It has the characteristic of  neutral stability (i.e., the aircraft’s tendency is to remain at  the new speed). The characteristics of flight in the region of reversed command  are illustrated at point B on the curve in  Figure 4-10 . If the  aircraft is established in steady, level flight at point B, lift is  equal to weight, and the power available is set equal to the  power required. When the airspeed is increased greater than  point B, an excess of power exists. This causes the aircraft  to accelerate to an even higher speed. When the aircraft is  slowed to some airspeed lower than point B, a deficiency  of power exists. The natural tendency of the aircraft is to  continue to slow to an even lower airspeed. This tendency toward instability happens because the  variation of excess power to either side of point B magnifies  the original change in speed. Although the static longitudinal  stability of the aircraft tries to maintain the original trimmed  condition, this instability is more of an influence because of  the increased induced drag due to the higher AOA in slow- speed flight. The term trim refers to employing adjustable aerodynamic  devices on the aircraft to adjust forces so the pilot does not  have to manually hold pressure on the controls. One means is  to employ trim tabs. A trim tab is a small, adjustable hinged  surface, located on the trailing edge of the elevator, aileron,  or rudder control surfaces. (Some aircraft use adjustable  stabilizers instead of trim tabs for pitch trim.) Trimming is  accomplished by deflecting the tab in the direction opposite  to that in which the primary control surface must be held.  The force of the airflow striking the tab causes the main  control surface to be deflected to a position that corrects the  unbalanced condition of the aircraft. Because the trim tabs use airflow to function, trim is a function  of speed. Any change in speed results in the need to re-trim the  aircraft. An aircraft properly trimmed in pitch seeks to return  to the original speed before the change. It is very important  for instrument pilots to keep the aircraft in constant trim. This  reduces the pilot’s workload significantly, allowing attention  to other duties without compromising aircraft control. Anytime an aircraft is flying near the stalling speed or the  region of reversed command, such as in final approach for a  normal landing, the initial part of a go around, or maneuvering  in slow flight, it is operating in what is called slow-speed flight.  If the aircraft weighs 4,000 pounds, the lift produced by the  aircraft must be 4,000 pounds. When lift is less than 4,000  pounds, the aircraft is no longer able to sustain level flight, and  consequently descends. During intentional descents, this is an  important factor and is used in the total control of the aircraft.  Slow-Speed Flight Reversed Command Trim Speed Stability Normal Command Region of normal command Region of reversed command Power deficit Excess power Airspeed  Little or no excess power or power deficit Power Required  Excess power B  C  A  Power deficit Figure 4-11.  Region of speed stability. 4-8