There is only one file type that uses the .NAS extension:
Nastran Input File
Input file used by MSC Nastran, a structural analysis program; contains input bulk data definitions referenced by MSC Nastran to analyze the stress and strain of component and system level models of structures; data appears in the FORTRAN programming language, which was originally developed by IBM, and stands for Formula Translating System; includes information such as the name of the bulk data, the number of grids, and the node locations of the elements that make up the models.
NOTE: The NAS file is similar to the .BDF and .DAT files, which are used to input data by MSC Nastran.
Updated: July 15, 2014