Altitude Elevation above sea level and air temperature, pressure and density. (C) (N/m2) (lb/ft2) a a. The ISA is based on the following International Standard Atmosphere (ISA) TablePerformance of the Jet Transport Airplane: Analysis Methods, Flight Operations and RegulationsWiley Online LibraryTable A. International Standard Atmosphere (ISA) (determined as a function of geopotential height, measured in feet) H. (ft) H T. (m) (K) T p p. (kg/m3) (slug/ft3) (m/s) (ft/s) − −E The pressure variatio