the mcdonnell douglas md-80 series, the second generation of the dc-9, began airline service in 1980. it was a lengthened dc-9-50 with a higher maximum take-off weight (mtow) and higher fuel capacity, as well as next-generation pratt and whitney jt8d-200 series engines and an improved wing design. 1,191 md-80s were delivered from 1980 to 1999.