In aviation, a stall refers to the aircraft's inability to remain in flight. Typically associated with airspeed, stall is the point where the aircraft wants to drop out of the sky. This has nothing to do with the engine running, as stall also affects non-engine powered, glider-type aircraft. As the airplane builds speed, the air pressure under the wing begins to push the plane upward. The pilot, in an attempt to create this lift at slower speeds, can put her flaps down to provide increased lift at slower speeds. When landing, the pilot takes the airplane to a point where it wants to teeter on the edge of flying and not flying, essentially stalling the plane in a controlled crash.
The aerodynamics of flight depend on the airflow of wind over the surface of a wing to create lift. This is the ability of the wind to support the weight of an aircraft. The initial lift is generated by the airplane as it speeds down a runway. As the speed increases, the wind flowing over the surface of the wing attempts to lift the plane skyward. The pilot is then charged with controlling the aircraft so that the wing can continue to support the weight of the plane as it gains speed and altitude. Attempting to climb too swiftly will place excessive drag on the wing, slowing the aircraft into a potential stall.
As a component in receiving a private pilot's license, the student pilot is required to stall a plane and regain control. This is a somewhat easy task, provided the pilot has enough altitude to correct the problem. A stall is commonly preceded by a slight buffeting of the aircraft as well as a sluggish feeling in the controls. As the aircraft begins to stall, the nose of the plane will drop. The pilot must take advantage of this nose drop to regain air speed and once again fly the plane.
While air speed is the main contributor to the stall, other factors such as weather and air currents can also factor into the loss of flight. Occasionally, the stall will be accompanied by a yaw, which will cause the aircraft to begin a spin. The pilot is forced to control the spin before addressing the stalling issue. This can often require more altitude that a common, small-engine aircraft is typically flown at, often resulting in a crash.