Three other teams in addition to Boeing have submitted proposals to NASA under the N+3 research programme, which set the challenge of designing a 2030-era aircraft that can satisfy anticipated commercial air transport needs while meeting specific energy efficiency, environmental and operational goals.

A team led by GE Aviation has proposed a 20-passenger turboprop aircraft aimed at reducing congestion at major hubs. The design anticipates using fuel cells to power the aircraft's electrical systems. Meanwhile, a Massachusetts Institute of Technology team envisages a 180-passenger aircraft termed the "double bubble" D8, which has two fuselages bonded together and three turbofan jet engines mounted on the tail. The engines would have an increased bypass ratio, achieved by minimising expansion of the engine's diameter and reducing the diameter of the jet exhaust.

The final team, led by Northrop Grumman, has submitted a design for a 120-passenger aircraft that it calls the Silent Efficient Low Emissions Commercial Transport (Select). The airframe Northrop Grumman proposes features ceramic composites, nanotechnology and shape memory alloys, and its power would be provided by a high-bypass ratio propulsion system.

NASA will select up to two of the four teams that entered proposals in phase one of the programme to participate in a second, three-year phase aimed at further developing the ideas. Phase two will begin in 2011.

Source: Flight International