When the airplane is flown at too slow an airspeed on the final approach, the pilot's judgment of the rate of sink (descent) and the height of roundout may be defective. During an excessively slow approach, the wing is operating near the critical angle of attack and, depending on the pitch attitude changes and control usage, the airplane may stall or sink rapidly, contacting the ground with a hard impact.
Whenever a slow speed approach is noted, the pilot should apply power to accelerate the airplane and increase the lift to reduce the sink rate and to prevent a stall. This should be done while still at a high enough altitude to reestablish the correct approach airspeed and attitude. If too slow and too low it is best to EXECUTE A GO-AROUND.