text: The proper coordination of the controls is 
  an absolute necessity during the approach. 
  In 
  this sense, due respect must be given to the 
  primary control of airspeed and race of descent 
  for the conditions of the steady approach. 
  Thus, the proper angle of attack will produce 
  the desired approach airspeed; too low an 
  angle of attack will incur an excess speed while 
  an excessive angle of attack will produce a 
  deficiency of speed and may cause stall or con- 
  trol problems. Once the proper airspeed and 
  angle of attack are attained the primary control 
  of rate of descent during the steady approach 
  will be the power setting. For example, if it 
  is realized that the airplane is above the de- 
  sired glide path, a more nose-down attitude 
  without a decrease in power setting will result 
  in a gain in airspeed. On the other hand, if it 
  is realized that the airplane is below the desired 
  glide path, a more nose-up attitude without an 
  increase in power setting will simply allow the 
  airplane to fly more slowly and-in 
  the region 
  of reversed command-eventually produce a 
  greater rate of descent. For the conditions of 
  steady flight, angle of attack is the primary 
  control of airspeed and power setting is the 
  primary control of rate of climb and descent. 
  This is especially true during the steady ap- 
  proach to landing. Of course, the ability of 
  to produce rapid changes in 
  the powerplant 
  thrust will affect the specific technique to be 
  used. If the powerplant is not capable of pro- 
  ducing immediate controlled changes in thrust, 
  the operating technique must’ account for this 