Complex sentence: This Master Plan was completed while General Aviation was booming across the country; a downturn in the economy affected General Aviation in the 1980s and through the early 1990s and the forecast growth did not materialize.
Split into simpler sentences: This Master Plan, however, was completed while General Aviation was booming across the country. A downturn in the general economy affected General Aviation in the 1980s and through the early 1990s and the forecast growth did not materialize.