McDonnell Douglas MD-12

The McDonnell Douglas MD-12 was a large wide-body airliner concept planned in the 1990s. It began as a trijet larger than the MD-11, called the MD-12X, and was then stretched into a four-engine design with two full-length passenger decks, similar in size to the Boeing 747 but with greater passenger capacity. The company agreed in October 1991 to offer the MD-12X to airlines and signed a memorandum of understanding with Taiwan Aerospace Corporation to form a joint company. The MD-12 never received an order and was canceled, after which the company studied larger MD-11 derivatives named MD-XX without proceeding.