The Boeing 737 Next Generation is unable to fit the criteria of a jet airliner.
Initial competition came from the smaller trijet widebodies: the Lockheed L-1011 (introduced in 1972), McDonnell Douglas DC-10 (1971) and later MD-11 (1990)
 The cost of the changes from previous 747 models, in particular the new wing for the 747-500X and -600X, was estimated to be more than US$5 billion

