text: From the previous analysis, it is apparent 
  that the cruise altitude of the turbojet should 
  be as high as possible within compressibility 
  or thrust limits. Generally, the optimum alti- 
  tude to begin cruise is the highest altitude at 
  the maximum continuous thrust can 
  which 
  provide the optimum aerodynamic conditions. 
  Of course, the optimum altitude is determined 
  mainly by the gross weight at the begin of 
  cruise. For the majority of turbojet airplanes 
  this altitude will be at or above the tropopause 
  for normal cruise configurations. 
  
  Most turbojet airplanes which have rran- 
  sonic or moderate supersonic performance will 
  obtain maximum range with a high subsonic 
  cruise. However, the airplane designed spe- 
  cifically for high supersonic performance will 
  obtain maximum 
  range with a supersonic 
  cruise and subsonic operation will cause low 
  lift-drag ratios, poor inlet and engine perform- 
  ance and redute the range capability. 
  
  The cruise control of the turbojet airplane 
  is considerably ~different from that of the pro- 
  peller driven airplane. Since the specific range 
  is so greatly affected by altitude, the optimum 
  altitude for begin of cruise should be attained 
  as rapidly as is consistent with climb fuel re- 
  quirements. The range-climb program varies 
  considerably between airplanes and the per- 
  formance section of the flight handbook will 
  specify the appropriate procedure. The de- 
  scent from cruise altitude will employ essen- 
  tially 
  the same feature, a rapid descent is 
  necessary to minimize the time at low altitudes 
  where specific’ range is low and fuel flow is high 
  for a given engine speed. 