In addition to the important factors of proper technique, many other variables affect the landing performance of an airplane. Any item which alters the landing speed or deceleration rate during the landing roll will affect the landing distance.The effect of gross weight on landing distance is one of the principal items determining the landing distance of an airplane. One effect of an increased gross weight is that the airplane will require a greater speed to support the airplane at the landing angle of attack and lift coefficient.The minimum landing distance will vary in direct proportion to the gross weight. For example, a 10 percent increase in gross weight at landing would cause:(1) a 5 percent increase in landing velocity.(2) a 10 percent increase in landing distance.The effect of wind on landing distance is large and deserves proper consideration when predicting landing distance. Since the airplane will land at a particular airspeed independent of the wind, the principal effect of wind on landing distance is due to the change in the ground speed at which the airplane touches down. The effect of wind on deceleration during the landing is identical to the effect on acceleration during the takeoff.A headwind which is 10 percent of the landing airspeed will reduce the landing distance approximately 19 percent but a tailwind which is 10 percent of the landing speed will increase the landing distance approximately 21 percent.The effect of pressure altitude and ambient temperature is to define density altitude and its effect on landing performance. An increase in density altitude will increase landing speed but will not alter the net retarding force. Since an increase in altitude does not alter deceleration, the effect of density altitude on landing distance would actually be due to the greater TAS (true airspeed).The minimum landing distance at 5000ft would be 16 percent greater than the minimum landing distance at sea level. The approximate increase in landing distance with altitude is approximately 3 and a half percent for each 1000ft of altitude. Proper accounting of density altitude is necessary to accurately predict landing distance.The effect of proper landing speed is important when runway lengths and landing distances are critical. The landing speeds specified in the airplane’s flight handbooks is generally the minimum safe speeds at which the airplane can be landed. Any attempt to land at below the specified speed may mean that the airplane may stall, be difficult to control, or develop high rates of descent. On the other hand, an excessive speed at landing may improve the controllability slightly, but will cause an undesirable increase in landing distance.5.Landing at below minimum safe speeds may result in （ ） ．