flat spin, is the most hazardous of all spins. In a flat spin, the  glider yaws around the vertical axis at a pitch attitude nearly  level with the horizon. A flat spin often has a very high rate of  rotation; the recovery is difficult, and sometimes impossible.  If a glider is properly loaded within its CG limits, entry into a  flat spin should not occur. Erect spins and flat spins can also  be inverted. The entry, wing form, and CG usually determine  the type of spin resulting from an uncoordinated wing stall. Since spins normally occur when a glider is flown in an  uncoordinated manner at lower airspeeds, coordinated use of  the flight controls is important. It is critical that pilots learn  to recognize and recover from the first sign of a stall or spin.  Entering a spin near the ground, especially during the landing  pattern, is usually fatal.  [Figure 3-33]  A pilot must learn to  recognize the warning signs, especially during the approach  and landing phase in a crosswind. A crosswind resulting in  a tailwind on the base leg may lead the pilot to tighten the  turn using rudder, or too steep a turn for the airspeed. An  uncoordinated turn could lead to the upper wing exceeding  its critical AOA before the lower wing, which could result  in a very high rate of roll towards the upper wing as the  upper wing stalls. If an excessive steep turn is attempted, the  glider may roll towards the inside wing or the outside wing  depending on the exact trim state at the instant of the stall.  Situational awareness of position to final approach should  be part of a before-landing routine. Ground effect is a reduction in induced drag for the same  amount of lift produced. Within one wingspan above the  ground, the decrease in induced drag enables the glider to fly  at a lower airspeed. In ground effect, a lower AOA is required  to produce the same amount of lift. Ground effect enables the  glider to fly near the ground at a lower airspeed and causes  the glider to float as it approaches the touchdown point. During takeoff and landing, the ground alters the three- dimensional airflow pattern around the glider. The result is  a decrease in downwash and a reduction in wingtip vortices.  Upwash and downwash refer to the effect an airfoil has on  the free airstream. Upwash is the deflection of the oncoming  airstream upward and over the wing. Downwash is the  downward deflection of the airstream as it passes over the  wing and past the trailing edge. Ground effect, in addition to the decrease in wind due to  surface friction and other terrain features upwind of the  landing area, can greater increase the landing distance of  a glider. A glider pilot, especially a visiting pilot, should  inquire about local effects from local pilots to enhance flight  planning and safe landings. During flight, the downwash of the airstream causes the  relative wind to be inclined downward in the vicinity of the  wing. This is called the average relative wind. The angle  between the free airstream relative wind and the average  relative wind is the induced AOA. In effect, the greater the  downward deflection of the airstream, the higher the induced  AOA and the higher the induced drag. Ground effect restricts  the downward deflection of the airstream, decreasing both  induced AOA and induced drag. Ground Effect 3-19