using equations, determine the temperature, pressure, and density of the air for an aircraft flying at 19.5 km. is this aircraft subsonic or supersonic? start from sea-level (sl) values: means you will have to go from sl to 11 km (one set of equations), then from 11 km to 19.5 (another set of equations). this is a two-step problem. for this problem, you should use the corresponding equations and not tables. if you solve the problem using tables and linear interpolation, you will get it wrong.