Recent forecasts have been that airline passenger traffic will almost triple by the year 2015 even if growth is less than the air transport industry's average of 5.5% over the last twenty years. This will lead to further increases in air traffic control system and airport congestion, forcing airlines to use larger aircraft than hitherto. Design teams on both sides of the Atlantic are working on concepts for ultra-high capacity airliners (UHCA) to satisfy the anticipated need. However, larger aircraft present major problems: taxiway and runway width limits, gate limits, passenger handling, emergency evacuation, community noise and aircraft separation due to wake vortices. Several different feasibility studies (occupying approximately 1,500 manhours each) have been carried out at the Royal Military College of Science into the design of UHCAs of broadly classical design. Each of the designs has been aimed at providing 600-700 tri-class seat/1000 economy seat transport aircraft. The topics of configuration, passenger cabin layout, and size constraints are addressed.