During the takeoff phase of flight, ground effect produces  some important relationships. An aircraft leaving ground  effect after takeoff encounters just the reverse of an aircraft  entering ground effect during landing. The aircraft leaving  ground effect will:  establishing a positive rate of climb and only after achieving  a safe altitude.  If, during the landing phase of flight, the aircraft is brought  into ground effect with a constant AOA, the aircraft  experiences an increase in C$_{L}$ and a reduction in the thrust  required, and a “floating” effect may occur. Because of the  reduced drag and lack of power-off deceleration in ground  effect, any excess speed at the point of flare may incur a  considerable “float” distance. As the aircraft nears the point  of touchdown, ground effect is most realized at altitudes less  than the wingspan. During the final phases of the approach  as the aircraft nears the ground, a reduction of power is  necessary to offset the increase in lift caused from ground  effect otherwise the aircraft will have a tendency to climb  above the desired glidepath (GP).  The axes of an aircraft are three imaginary lines that pass  through an aircraft’s CG. The axes can be considered as  imaginary axles around which the aircraft turns. The three  axes pass through the CG at 90° angles to each other. The  axis passes through the CG and parallel to a line from nose  to tail is the longitudinal axis, the axis that passes parallel  to a line from wingtip to wingtip is the lateral axis, and the  axis that passes through the CG at right angles to the other  two axes is the vertical axis. Whenever an aircraft changes  its flight attitude or position in flight, it rotates about one or  more of the three axes.  [Figure 5-18]  The aircraft’s motion about its longitudinal axis resembles  the roll of a ship from side to side. In fact, the names  used to describe the motion about an aircraft’s three axes  were originally nautical terms. They have been adapted to  aeronautical terminology due to the similarity of motion of  aircraft and seagoing ships. The motion about the aircraft’s  longitudinal axis is “roll,” the motion about its lateral axis is  Ground effect must be considered during takeoffs and landings.  For example, if a pilot fails to understand the relationship  between the aircraft and ground effect during takeoff, a  hazardous situation is possible because the recommended  takeoff speed may not be achieved. Due to the reduced drag  in ground effect, the aircraft may seem capable of takeoff well  below the recommended speed. As the aircraft rises out of  ground effect with a deficiency of speed, the greater induced  drag may result in marginal initial climb performance. In  extreme conditions, such as high gross weight, high density  altitude, and high temperature, a deficiency of airspeed during  takeoff may permit the aircraft to become airborne but be  incapable of sustaining flight out of ground effect. In this case,  the aircraft may become airborne initially with a deficiency  of speed and then settle back to the runway.  A pilot should not attempt to force an aircraft to become  airborne with a deficiency of speed. The manufacturer’s  recommended takeoff speed is necessary to provide adequate  initial climb performance. It is also important that a definite  climb be established before a pilot retracts the landing gear  or flaps. Never retract the landing gear or flaps prior to  Figure 5-18.  Axes of an airplane.  5-12  Axes of an Aircraft  • Require an increase in AOA to maintain the same C$_{L }$ • Experience an increase in induced drag and thrust  required  • Experience a decrease in stability and a nose-up  change in moment  • Experience a reduction in static source pressure and  increase in indicated airspeed  Pitching  Rolling  Yawing  Lateral axis  Longitudinal axis  Vertical axis 