Leeham News and Analysis
There's more to real news than a news release.
Perspective on Boeing’s 737 replacement
By Scott Hamilton
Sept. 30, 2025, © Leeham News: The Wall Street Journal billed the story as an exclusive, and it did contain details previously unreported.
But the fact that Boeing is working on a 737 replacement isn’t new, even if Boeing has been super-quiet about it. The breadcrumbs have been dropped into public sight all along, and within aviation circles, more has been discussed as well.
Under former CEO David Calhoun, he and other executives discussed the 737 replacement in the form of the transonic truss brace wing (TTBW) single-aisle concept. The very wide, thin wing had about 35 feet of folding wing (as opposed to the folding wing tips on the 777X).
Boeing and Airbus are designing future wings with long folds to allow much greater wingspan than today’s wings. The future folding wings will have a much long fold than the Boeing 777X. Credit: Leeham News.
What Boeing didn’t say publicly, but which was known within aviation circles, was that Boeing was also designing a conventional wing-and-tube 737 replacement in parallel. Boeing always has a Plan A and a Plan B under study, so this was no surprise. But a former 737 program engineer told LNA that Boeing needed a Plan B in this case to serve as a baseline against which the TTBW could be compared for efficiency.
When Calhoun’s successor, Kelly Ortberg, killed the TTBW, Boeing said research and development on the wing would continue. Of course, it would be a replacement for a 737. Why else continue this very specific R&D? Not inconsequentially, Airbus has long been designing a folding wing “Wing of Tomorrow” for the A320 replacement.
Furthermore, the underlying research into the TTBW’s fuselage and systems may be applied to a new airplane, just as elements of the Sonic Cruiser made their way into the 787 in the early 2000s.
Bjorn’s Corner: Faster aircraft development. Part 9. Conceptual phase Certification work.
By Bjorn Fehrm and Henry Tam
September 26, 2025, ©. Leeham News: We do a series about ideas on how the long development times for large airliners can be shortened. New project talks about cutting development time and reaching certification and production faster than previous projects..
The series will discuss the typical development cycles for an FAA Part 25 aircraft, called a transport category aircraft, and what different ideas there are to reduce the development times.
We will use the Gantt plan in Figure 1 as a base for our discussions.
Figure 1. A generic new Part 25 airliner development plan. Source: Leeham Co. Click to see better.
*** Special thanks to Andrew Telesca for helping with this article***
Bjorn’s Corner: Air Transport’s route to 2050. Part 5.
By Bjorn Fehrm
January 17, 2025, ©. Leeham News: We do a Corner series about the state of developments to replace or improve hydrocarbon propulsion concepts for Air Transport. We try to understand why the development has been slow.
We have covered why the technical progress of battery-based aircraft has been slow. Now we look at what type of missions it can do this decade and beyond and why the limitations.
Figure 1. The Diamond eDA40 electric trainer. Source: Diamond. Read more
Bjorn’s Corner: New aircraft technologies. Part 40. The initial production crisis
By Bjorn Fehrm
December 01, 2023, ©. Leeham News: We are discussing the different phases of an airliner development program. After covering Conceptual, Preliminary, and Detailed design, the manufacturing of prototypes, and their roles in flight tests, we now look at Production.
Last week, we explained why the focus on the production phase has increased for recent and future projects. Now we go deeper into why the production phase and how it runs is so important.
Figure 1. The development plan for a new airliner. Source: Leeham Co.
The Small Airliner Problem, Part 3
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By Bjorn Fehrm
May 4, 2023, © Leeham News: In our series about the viability of the business plans for small airliners (nine to 50 seats), we have covered how energy and fuel consumption scales with the size of the airliner.
The cost factor we examine today is the maintenance cost for keeping an airliner fit for purpose and safe.
We use the Leeham aircraft performance and cost model to get the data for the maintenance costs for airliners going from nine to 200 seats.
Figure 1. The Cessna Sky Courier is a new 19-seat small airliner with conventional propulsion. Source: Textron Aviation.
Summary:
- The maintenance costs of an airliner scale differently from the energy and fuel consumption we studied last week.
- We discuss the scaling metrics for the airframe maintenance costs and how these differ from what drives engine maintenance costs.
Bjorn’s Corner: New aircraft technologies. Part 10. Engine choice
By Bjorn Fehrm.
April 28, 2023, ©. Leeham News: This is a summary of the article New aircraft technologies. Part 10P. Engine choice. The article discusses the engine architecture choices that must be made when developing the next-generation airliners.
Figure 1. The Pratt & Whitney high bypass geared turbofan technologies. Source: Pratt & Whitney.
Boeing’s Renton plant may close from 2033: Analysis
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Introduction
Aug. 10, 2020, © Leeham News: With Boeing likely to consolidate 787 production in Charleston (SC), reflecting a rate of 6/mo, the future of assembly in Puget Sound rears its head again.
LNA outlined Aug. 3 why Everett is the ideal location to assemble the Next Boeing Airplane (NBA).
Boeing’s product line also requires a new airplane in the 100-150 seat sector. Airbus’ A220-100/300 and, nominally, the A320neo (but not the A319neo) fill this sector. (The A320neo was originally designed as a 150-seat airplane. It now is commonly configured in the 150-180 seat size.)
Airbus has a design for an A220-500, which could replace the A320.
Boeing’s Renton (WA) 737/757 plant footprint in 1990. Source: Google Earth.
Boeing needs an efficient competitor to the current A220 plus a replacement for the 737-7 and, eventually, the -8.
And it probably won’t be assembled at the Boeing 737 plant in Renton.
Summary
- Boeing-Embraer JV was to focus on 100-150 seat airplane.
- Canceled deal could be revived.
- Or Boeing could choose a new partner.
- Moonshot would be two roughly concurrent new airplane programs.