The McDonnell Douglas DC-9 (initially the Douglas DC-9) is a single-aisle airliner designed by the Douglas Aircraft Company.After introducing its heavy DC-8 in 1959, Douglas approved the smaller, all-new DC-9 for shorter flights on April 8, 1963.The DC-9-10 first flew on February 25, 1965 and gained its type certificate on November 23, to enter service with Delta Air Lines on December 8.With five seats across in economy, it had two rear-mounted Pratt & Whitney JT8D turbofans under a T-tail for a cleaner wing, a two-person flight deck and built-in airstairs.