Leeham News and Analysis
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Bjorn’s Corner: Faster aircraft development. Part 25. The Difference between Continuing and Continuous Airworthiness.
By Bjorn Fehrm
January 39, 2026, ©. Leeham News: We have done a series about ideas on how the long development times for large airliners can be shortened, while at the same time describing all the regulatory work that must be done, regardless of work practices.
It’s now time to sum up what we have looked at in terms of speeding up the development of a Part 25 Air Transport airliner in the 200-seat segment. But before we do that, we will look at what an operator of the aircraft we have delivered will have to do to qualify it for operation with its local regulator.
For an operator to operate our aircraft, Continued Airworthiness, as described in last week’s article, is not enough; the Operator must add what can be called Continuing Airworthiness. These words are close but not the same, and there is a substantial difference in what’s behind them.
Pratt & Whitney builds for the future while wrestling with the present
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By Bjorn Fehrm and Charlotte Bailey
January 26, 2026, © Leeham News: Pratt & Whitney (PW) bet big on the geared turbofan to take it back to a sizeable position in the market’s largest airliner segment, the Single-Aisle. It spent more than 20 years to develop the fan gearbox, including functional demonstrator engines that flew on Airbus test aircraft to prove the technology.
The effort was a success; the gearbox in the Pratt & Whitney range of Geared TurboFans, GTFs, has worked perfectly. It achieved what was promised, a low fuel consumption, and has been rock-solid in its function.
Yet PW’s GTFs have had a range of problems since their introduction in 2016. Bent main shafts, combustors that burn through, bearings that fail. And on top, a huge call-back of engines, as a contaminated power metal process has produced compressor and turbine discs that risk failing before their on-engine life expires. The situation has caused over 600 Airbus A320 and A321neos with GTF engines to be grounded for engine replacements, if and when replacement discs are available.
The issues, stemming from the “business as usual” parts of the GTF, have led to write-offs of billions of dollars for PW’s mother RTX and to lost market share to the competing CFM LEAP engine on the Airbus A320/321neo series. But while this clouds the business of yesterday and today, Pratt & Whitney still has the clout to invest in the future. Being part of one of the World’s largest Defence and Aerospace Companies is an important part of the answer.
Figure 1. The Maeve MJ500 with the revolutionary Pratt & Whitney Canada Constant Volume Open Fan engine. Source: Maeve. Read more
Bjorn’s Corner: Faster aircraft development. Part 24. Post certification, Sustainment phase.
By Bjorn Fehrm and Henry Tam.
January 23, 2026, ©. 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 looked at the preparation work around entry into service; now we talk about post-certification work and the support of the new airliner generating revenue flights for the airline customer.
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 23. Preparing for Entry Into Service.
By Bjorn Fehrm and Henry Tam
January 16, 2026, ©. 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 looked at the production preparations and the challenges of the serial production phase. Now we look a the preparation work around entry into service for our new airliner.
Figure 1. A generic new Part 25 airliner development plan. Source: Leeham Co. Click to see better.
Bjorn’s Corner: Faster aircraft development. Part 22. Serial Production.
By Bjorn Fehrm and Henry Tam.
January 9, 2026, ©. 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 completed flight testing of the flight test aircraft and obtained a design Type Certificate (TC). We now examine the production preparations and the serial production 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 20. Flight Testing.
by Bjorn Fehrm and Henry Tam
December 12, 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 completed the articles on Prototype Manufacturing and Ground Vibration Tests (GVT). We now conduct the program’s flight tests with the manufactured test aircraft.
Figure 1. A generic new Part 25 airliner development plan. Source: Leeham Co. Click to see better.
Bjorn’s Corner: Faster aircraft development. Part 19. Flight Test Aircraft Assembly.
December 5, 2025, ©. Leeham News: We do a series on ways to shorten the long development times for large airliners. New projects aim to cut development time and achieve 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 the different approaches to reducing development time.
We will use the Gantt plan in Figure 1 as a base for our discussions. We have exited the Detailed Design phase after conducting Critical Design Reviews, CDRs, and now enter into Prototype Manufacturing. After reviewing the acceptance and testing of the first parts and systems from suppliers, we now discuss putting together the first flight-test aircraft.
Figure 1. A generic new Part 25 airliner development plan. Source: Leeham Co. Click to see better.
** Special thanks to Ron Everlove for helping with this article **
The state of alternative propulsion aircraft? Part 3.
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By Bjorn Fehrm
November 27, 2025, © Leeham News: In our series about alternative propulsion aircraft, last week we looked at the electric motor of an electric aircraft, which drives propellers or fans. It’s a component that is straightforward to develop, but the certification requirements for the aircraft and VTOL industry have slowed progress.
Now we look at the component that causes trouble for all alternative propulsion aircraft, except those that burn hydrogen in gas turbine engines: the batteries. Batteries work well in cars, where the requirement for energy capacity relative to weight is much lower and where energy recovery during braking reduces the energy required from the battery.
Figure 1. The battery-electric aircraft that flies operational trials as we speak, the Beta Technologies Alia CX300. Source: Leeham Co.
Aircraft batteries are a heavy component with very low energy storage capacity. Today’s aircraft battery system has about 60 times lower energy density per kg or lb than aircraft fuel.
The hope over the last decade has been that this relationship should improve. It has, it’s gone from about 70 times to 60 times in the last 10 years. This will improve further, the question is if it will continue at the slow pace of the last 10 years or not?
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.
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.