text: airplane will have a maximum specific endur- 
  ance at 35,ooO ft. which is at least 40 percent 
  greater than the maximum value at sea level. 
  If the turbojet airplane is at low altitude and 
  it is necessary to hold for a considerable time, 
  maximum time in the air will be obtained by 
  beginning a climb to some optimum altitude 
  dependent upon the fuel quantity available. 
  Even though fuel is expended during the climb, 
  the higher altitude will provide greater total 
  endurance. Of course, the use of afterburner 
  for the climb would produce a prohibitive re- 
  duction in endurance. 
  OFl4X’TIMUM 
  ANCE 
  
  to airplane factors. The turboprop power- 
  plant prefers operation at low inlet air tem- 
  peratures and relatively high power setting to 
  produce low specific fuel consumption. While 
  increase the mini- 
  an increase in altitude will 
  mum power required for 
  the 
  the airplane, 
  powerplant achieves more efficient operation. 
  As a result of these differences, maximum en- 
  durance of the multiengine turboprop airplane 
  at low altitudes may require shutting down 
  some of the powerplants in order to operate 
  the remaining powerplants at a higher, more 
  efficient power setting. 