Leeham News and Analysis
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Bjorn’s Corner: Faster aircraft development. Part 17. Critical Design Review, CDR.
By Bjorn Fehrm and Henry Tam
November 21, 2025, ©. Leeham News: We do a series about ideas on how the long development times for large airliners can be shortened. New projects talk 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. We are in the Detailed Design phase, and it’s time to conduct the Critical Design Reviews, CDRs.
Figure 1. A generic new Part 25 airliner development plan. Observe the CDRs. Source: Leeham Co. Click to see better.
The state of alternative propulsion aircraft? Part 2.
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By Bjorn Fehrm
November 20, 2025, © Leeham News: In our series about alternative propulsion aircraft, we started last week by discussing what happened after the trigger by the Airbus E-fan flight in 2014 and the introduction of the Tesla Model S car two years before. The alternative propulsion aircraft projects that followed had a rocky path. They followed the Gartner Hype-curve, Figure 1.
There were hundreds of projects announced, more or less serious. A few of these came to producing hardware, and flew test flights, then stopped. Most stayed as PowerPoint presentations and fancy renderings, promising capabilities that were not possible to realize. The result was that we passed the Peak of Inflated Expectations and entered the Trough of Disillusionment. Investors fled to AI, and projects froze or stopped.
Figure 1. The Gartner Hype-curve. Source: Gartner Inc.
By 2025, we are in the Disillusionment phase. As there are signs we can now enter a phase of real, sustainable progress, it’s timely to take stock of where we are and what progress we can expect over the next decade.
To understand why progress has been so difficult, after explaining that learnings from Cars are not transferable last week, we start by focusing on two components that we find in every alternative propulsion concept, the Electric Motor and the Battery system. Of the two components, the motor is the most straightforward to develop and certify for an aircraft. Still, we have only limited progress so far, and we detail why in today’s article.
The Battery System is the most challenging component for alternative propulsion aircraft, both in development and in use. We will spend next week’s article detailing why and how it has slowed down progress so far, and how this can change going forward.
Bjorn’s Corner: Faster aircraft development. Part 16. Certification Compliance Planning.
By Bjorn Fehrm and Henry Tam
November 14, 2025, ©. Leeham News: We do a series about ideas on how the long development times for large airliners can be shortened. New projects talk 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. We are in the Detailed Design phase and working with the Certification Compliance plan.
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 ***
What’s the status of the alternative propulsion projects for air transport?
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By Bjorn Fehrm
November 13, 2025, © Leeham News: The interest for new and more environmentally friendly aircraft got underway in 2014, when Airbus flew the battery-electric E-fan demonstrator at the Farnborough Air Show in July, Figure 1.
The car revolution to battery-electric cars had taken off two years earlier, when Tesla introduced the Model S sedan with elegant styling and very good performance and economy for a family car (Figure 1).
Figure 1. The battery-electric aircraft demonstrator and the car that started it all. Credit: Airbus and Tesla Inc.
Tesla cars had proven that electric cars could match and even outpace combustion-engine cars in performance and operational costs, though not in driving range. But range was a matter of battery capacity development, and hopes were high for a similar situation and development for aircraft.
As is the case with almost every technological leap, the progression of alternative propulsion aircraft projects followed the Gartner Technology Hype curve (Figure 2).
Figure 2. The Gartner Hype Curve for alternative propulsion aircraft. Credit: Gartner and Leeham Co.
The start was around 2015, passing the Peak of Inflated Expectations around 2020. In the 11 years since 2014, we’ve had hundreds of entrepreneur-driven projects declare they will make environmentally friendly aircraft and airliners a reality.
Nothing useful has come out of these projects, so today, we are passing the Trough of Disillusionment. Investors have stopped funding alternative propulsion startups as these have not produced useful air transport. The result is a mass death of projects, most silently, some more openly.
The core of the remaining projects are run by experienced teams with solid aeronautical knowledge. These are now passing into the Slope of Enlightenment and will make real progress. Given that we are now entering a more productive phase, we take stock of these developments and their programs.
To help the analysis, we use our Aircraft Performance and Cost Model, APCM, to show what the challenges are and how alternative propulsion can address these challenges.
Bjorn’s Corner: Faster aircraft development. Part 14. Detailed Design.
October 31, 2025, ©. Leeham News: We do a series about ideas on how the long development times for large airliners can be shortened. New projects talk 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.
We have exited the Preliminary Design phase through the Preliminary Design Reviews, PDRs, and now enter the Detailed Design phase.
Figure 1. A generic new Part 25 airliner development plan. Source: Leeham Co. Click to see better.
Bjorn’s Corner: Faster aircraft development. Part 13. Preliminary Design Review, PDR.
By Bjorn Fehrm and Henry Tam
October 24, 2025, ©. Leeham News: We do a series about ideas on how the long development times for large airliners can be shortened. New projects talk 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. Today’s topic, the Preliminary Design Reviews, PDRs, are marked in the chart.
Figure 1. A generic new Part 25 airliner development plan with PDR marked in time. Source: Leeham Co. Click to see better.
Bjorn’s Corner: Faster aircraft development. Part 12. Preliminary Design; Requirements Definition.
By Bjorn Fehrm and Henry Tam
October 17, 2025, ©. Leeham News: We do a series about ideas on how the long development times for large airliners can be shortened. New projects talk 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. We added two milestones to our Program Plan, which we will refer to in the articles: Preliminary Design Review and Critical Design Review. Here is their definition according to NASA:
The Preliminary Design Review (PDR) demonstrates that the preliminary design meets all system requirements with acceptable risk and within the cost and schedule constraints, and establishes the basis for proceeding with detailed design. It shows that the correct design options have been selected, interfaces have been identified, and verification methods have been described. The PDR should address and resolve critical, system-wide issues and show that work can begin on detailed design.
The Critical Design Review (CDR) demonstrates that the maturity of the design is appropriate to support proceeding with full-scale fabrication, assembly, integration, and test. CDR determines if the technical effort is on track to complete the system development, meeting mission performance requirements within the identified cost and schedule constraints.
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: Faster aircraft development. Part 11. Interior Preliminary Design.
By Bjorn Fehrm and Henry Tam
October 10, 2025, ©. Leeham News: We do a series about ideas on how the long development times for large airliners can be shortened. New projects talk 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.
Bjorn’s Corner: Faster aircraft development. Part 10. Preliminary design.
By Bjorn Fehrm and Henry Tam
October 3, 2025, ©. Leeham News: We do a series about ideas on how the long development times for large airliners can be shortened. New projects talk 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.
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***