NASA report from Aug 01, 1988 reports a linear aircraft model flying over a flat, nonrotating earth "Derivation and definition of a linear aircraft model"

"A linear aircraft model for a rigid aircraft of constant mass flying over a FLAT, NONROTATING earth is derived and defined. The derivation makes no assumptions of reference trajectory or vehicle symmetry. The linear system equations are derived and evaluated along a general trajectory and include both aircraft dynamics and observation variables. "
Last page of the report

Why would an aircraft fly over a flat, nonrotating earth??? Well, cuz it is FLAT and NONROTATING?!

I've attached 2 links of the Document, one containing 108 pages and one 102, one from NASA Technical Report Server and the other from the official site.
https://ntrs.nasa.gov/search.jsp?R=19890005752
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890005752.pdf
https://www.nasa.gov/centers/dryden/pdf/88104main_H-1391.pdf

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