Well Joyce … first off the design of the Boeing 747 was actually designed for cargo and cargo conversion purposes rather than pure passenger deployment. The upper deck on the 747 was to allow a raised cockpit over a full opening nose section, allowing for the loading of massive cargo loads … but that random 747 fact aside, a viable modern double-decker jetliner had been created, just never built, prior to the Airbus A380.
The MD-12 design was 208 feet in length with a wingspan of 213 feet, and a passenger capacity of 430 passengers in a three-class cabin. If the MD-12 were ever put into production, it would have competed directly with Boeing 747-400 that entered service in 1989. The 747-400 (the current generation 747 still in service with airlines today) has a fuselage length of 231 feet 10 inches and a wingspan of 211 feet 5 inches, and a capacity of 416 passengers in three classes.
The MD-12′s intended range was fairly comparable to the 747-400 (the 747-400ER had not yet been designed or released) at 7,170 nautical mile, where as the 747-400′s range is 7,260 nautical miles.
Had the MD-12 been created it is likely it’s range would have been increased to match the 747-400, as well an ER variant and larger capacity variant would have been designed as well.
The engine intended for the MD-12 was the General Electric CF6-80C2, which was the primary engine utilized by the DC-10, and is still a popular engine with airlines, currently in use with Boeing 747, Boeing 767 and Airbus A330 aircraft.
An area in which the MD-12 would have been significantly superior to the 747-400 was its maximum take off weight of 949,000lbs, compared to the 747-400′s 875,000 lb (the current maximum weight of the 747-400ERF cargo aircraft is 910,000lbs). This significant improvement in maximum take off weight would have made the aircraft superior in terms of carrying additional belly cargo with full passenger loads, increasing an airline’s potential in maximizing its revenue per flight.
The MD-12′s intended first flight was 1995, with deliveries intended roll out to airlines in 1997, however once the project was undertaken it was determined that the investment costs into the MD-12 would be to large for the company that was already experiencing financial difficulties.
The design of the MD-12 is remarkably similar to that of the current Airbus A380, however the current aircraft we know as the A380 is quite a bit larger than the MD-12. The A380-800 is 238.6 feet long, a wingspan of 261.6 feet and a 3-class passenger capacity of 525 passengers. In terms of maximum weight…the A380, which had its initial commercial introduction to airlines 3 years after McDonnell Douglas merged with Boeing … beats the MD-12 hands down, with a maximum take off weight of 1,250,000lbs
…so where was I? Oh yes, while there have been many double-decker seaplanes like the Boeing 314; the MD-12 was almost the first full double-decker modern jet aircraft.
On a side note, aircraft designs like the MD-12 and A380 cannot fully realize their cargo potential due to the positioning of the cockpit. The cockpit placement on the MD-12 and A380 design does not allow for the nose to be opened up. A non-opening hinged nose significantly limits the potential for loading vary large payloads into the aircraft and maximizing the full space potential of the main deck cargo area.
Below are three original McDonnell Douglas artist renditions of the MD-12…that never was meant to be.