text: At low flight speeds during approach, land- 
  ing, and takeoff, the effect of the vertical gust 
  is due to the same mechanism of the change 
  in angle of attack. However, at these low 
  flight speeds, the problem is one of possible 
  than 
  rather 
  incipient stalling and sinking 
  overstress. When 
  is at high 
  angle of attack, a further increase in angle of 
  attack due to a gust may exceed the critical 
  angle of attack and cause an incipient stalling 
  of the airplane. Also, a decrease in angle 
  of attack due to a gust will cause a loss of lift 
  to sink. For this 
  and allow 
  reason, any deficiency of airspeed will be quite 
  critical when operating in gusty conditions. 
  The effect of the hori<oonral gust differs from 
  the effect of the vertical gust in that the im- 
  mediate effect is a change of airspeed rather 
  than a change in angle of attack. 
  In this 
  sense, the horizontal gust is of little conse- 
  quence in 
  the major airplane airloads and 
  strength limitations. Of greater significance 
  is the response of the airplane to horizontal 
  gusts and wind shear when operating at low 
  flight 
  in 
  which an airplane may encounter horizontal 
  gusts and wind shear are illustrated in figure 
  6.5. As the airplane traverses a shear of wind 
  direction, a change in headwind component 
  will exist. Also, a climbing or descending 
  airplane may traverse a shear of wind velocity, 
  i.e., a wind profile in which the wind velocity 
  varies with altitude. 