Complex sentence: The Ag Cat was the first aircraft specifically designed by a major aircraft company for agricultural aviation, the first aircraft designed according to the regulations of Civil Aeronautics Manual Part 8, which had been written especially for agricultural aircraft.
Split into simpler sentences: The Ag Cat was the first aircraft specifically designed by a major aircraft company for agricultural aviation. The AG-Cat was the first aircraft designed according to the regulations of Civil Aeronautics Manual Part 8, which had been written especially for agricultural aircraft.