text: INDICATOR. 
  Many specific aerodynamic conditions exist at 
  particular angles of attack for the airplane. 
  Generally, the conditions of stall, landing ap- 
  proach, takeoff, range, endurance, etc., all 
  occur at specific values of lift coefficient and 
  specific airplane angles of attack. Thus, an 
  instrument to indicate or relate airplane angle 
  of attack would be a valuable reference to aid 
  the pilot. 
  
  When the airplane is at high angles of attack 
  it becomes difficult to provide accurate indica- 
  tion of airspeed because of the possibility of 
  large position errors. 
  In fact, for low aspect 
  ratio airplane configurations at high angles of 
  attack, it is possible to provide indications of 
  angle of attack which are more accurate than 
  indications of airspeed. As a result, an angle 
  of attack indicator can be of greatest utility ar 
  the high angles of attack. 
  
  357 