The extension .SPB refers to files of the type, Flight simulator Mission files.This is a data file that stores the state of the gameplay and the mission information for few of the popular flight simulation games.

The file is usually created by Microsoft ESP which is a toolkit for generating flight simulation maps and stages. The file structure is mostly based on the xml format and is followed in the same pattern by the ESP program. The final result may also be stored in the form of a binary executable file SPB format.