American, Delta and United each have dozens of 757s in their respective fleets, although each aircraft's routine maintenance costs can be astronomical. Boeing hoped airlines would order its larger 787-8 Dreamliner or the smaller 737-900, but instead, many airlines — including some loyal Boeing customers — opted for the A321 from Airbus, which is nearly equivalent, in terms of size and range capability, to the 757. Since the end of 757 production, Boeing has lacked a so-called Middle-of-Market (MoM) aircraft in its stable. Airlines have asked Boeing to either create a modern version of the aircraft or launch a clean-sheet design of an all-new plane to act as a replacement for both the 757 and the wide-body 767.
United Airlines' CFO, Andrew Levy, recently said in an interview with Bloomberg, that United had been shown a design for a newly-designed plane, which could potentially fly eight years from now. Boeing's VP Marketing Randy Tinseth offered a few vague hints at what this aircraft may eventually become. "One will be bigger and fly not quite as far, one will be smaller and fly farther," he said. "To some extent you address the single-aisle market, to some extent you address the wide-body market and to some extent you are stimulating growth where no one has been before. And that has been a fascinating part of the whole project."
This "paper plane" (meaning the aircraft exists on paper only at this time) would almost surely be called the 797, and would likely have two aisles in the cabin with seven or eight seats in each row arranged in a 2-3-2 or 2-4-2 configuration. A twin-aisle aircraft allows for more efficient boarding and disembarkation versus a longer, single-aisle plane.
H/T: Bloomberg
