text: The specific endurance is simply the reciprocal 
  of the fuel flow, hence maximum endurance 
  conditions would be obtained at the lowest 
  fuel flow required to hold the airplane in steady 
  level flight. Obviously, minimum fuel flow 
  will provide the maximum flying time from a 
  given quantity of fuel. Generally, in subsonic 
  performance, the speed at which maximum en- 
  durance is achieved is approximately 75 per- 
  cent of the speed for maximum range. 