Regions of Command
The drag curve also illustrates the two regions of command:
the region of normal command, and the region of reversed
command. The term "region of command" refers to the
relationship between speed and the power required to
maintain or change that speed. "Command" refers to the input
the pilot must give in terms of power or thrust to maintain a
new speed once reached.

The "region of normal command" occurs where power must
he added to increase speed. This region exists at speeds higher
than the minimum drag point primarily as a result of parasite
drag, the "region of reversed command" occurs where
additional power is needed to maintain a slower airspeed.
This region exists at speeds slower than the minimum drag
point (L/Dmax) on the thrust required curve, Figure 2-8 and
is primarily due to induced drag, Figure 2-9 shows how one
power setting can yield two speeds, points 1 and 2. This is
because at point 1 there is high induced drag and low parasite
drag, while at point 2 there is high parasite drag and low
induced drag.

Figure 2-9. Regions of Command.

Control Characteristics
Most flying is conducted in the region of normal command:
for example, cruise, climb, and maneuvers. The region of
reversed command may be encountered in the slow-speed
phases of flight during takeoff and landing; however, for
most general aviation aircraft, this region is very small and
is below normal approach speeds.

Flight in the region of normal command is characterized
by a relatively strong tendency of the aircraft to maintain
the trim speed. Flight in the region of reversed command is
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.

Speed Stability
Normal Command
The characteristics of flight in the region of normal command
are illustrated at point A on the curve in Figure 2-10. 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.