Boeing opted to re-engine the 737 rather than build an all-new narrowbody because the production system for a new aircraft was not ready.
Speaking at a press conference to discuss American Airlines' order for 100 re-engined 737s plus 60 options, Boeing Commercial Airplanes chief executive Jim Albaugh said that "while the technology was there" to develop an all-new narrowbody, the "production system is not understood".
He added that after speaking with customers "who want certainty" on delivery schedules, the manufacturer opted to proceed with the re-engined 737.
Boeing now has to complete configuration of the re-engined 737 "over the next several weeks" and secure approval from the board.
The airframer aims to launch the programme "some time this fall", said Albaugh.
The re-engined 737 will be powered by the CFM International Leap-X engine.
Albaugh said that Boeing has had "a number of preliminary discussions" with other carriers about the planned re-engined 737.