1990 CE
All domestic flight of 6 hours or less become smoke-free

According to federal law, all domestic airline flights of six hours or less are now to be smokefree (the ban takes effect on February 25th). The law affects all but 28 of the 16,000 domestic flights in the U.S., making almost every domestic flight smoke-free. In addition, smoking is also banned on interstate buses.

Source: Smokefree Transportation Chronology (2005). Americans for nonsmokers' rights.