The McDonnell Douglas MD-80 is a twin-engine, medium-range, single-aisle commercial jet airplanes. The MD-80 aircraft was originally part of the DC-9 line when first delivered before being later renamed. The MD-80 series have seating capacity up to 172 passengers. They have a common cabin layout that seats 140 passengers on scheduled flights and 161 or 165 on low-cost or charter flights. The Alaska Airlines flew MD-80 aircraft on the routes more than 92 cities in the United States, Canada and Mexico. Alaska airlines operates a fleet of Boeing 737 and MD-80. The airline ultimately plans to replace all MD-80 aircraft with Boeing 737-800s by the end of 2008. The retired MD-80s will be stored in Mojave Spaceport in Mojave, California or Southern California Logistics Airport in Victorville, California. The MD-80 series was derived from the DC-9 and it was introduced commercially in October 1980 by Swissair. It entered service in 1980. The MD-80 versions have cockpit, avionics and aerodynamic upgrades along with the more powerful, efficient and quieter JT8D-200 series engines. The MD series aircraft also have longer fuselages than their earlier DC-9 counterparts, as well as longer range. The MD-80 series has been used by airlines around the world. The MD-80 series production ended in 1999. Notably, some customers, American Airlines and Alitalia still, as of 2007, refer to the planes in fleet documentation as "Super 80" or "SP80". The MD-80 model is still flown extensively by American Airlines and Delta Airlines on domestic routes.