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.

Preliminary Design

After completing the Conceptual Design and receiving the go-ahead from the company, we can kick off activities for the Preliminary Design phase.

Overview of Preliminary Design

The Preliminary Design generates the next level of details for the aircraft.  In order to create these details, suppliers are now getting more involved.  This means that they begin deploying more resources to support the program.

An aircraft OEM also needs to ramp up its team.  The OEM must have sufficient resources to collaborate with suppliers, carry out integration activities, work with certification authorities, and develop solid plans in many domains.  As a result, the spending begins to increase.

Aircraft Design

Defining the certification bases and aircraft integration are some of the main themes for this phase.  We will save certification activities for a future article and focus on aircraft integration for this article.

Interface definition is an excellent example of the challenges associated with integration.  These interfaces include mechanical, electrical, and software interfaces.  The team has started initial interface evaluations during the last phase, and they are expected to be baselined by the end of this phase.

Mechanical interfaces are relatively easy to understand.  For example, to join the wing to the fuselage, structures teams, along with supporting functions, need to conduct analyses to evaluate attachments and attachment points.  There are also other interfaces between the wing and the fuselage to be examined.  Openings to allow wires, fuel lines, hydraulic lines, and pneumatic ducts to pass through must match up as well. These teams must work together to synthesize the information and resolve various challenges, such as eliminating physical interferences or avoiding stay-out zones.  The results are then formally documented to ensure all teams are working with the same assumptions going forward.

Similarly, there are Subject Matter Experts (SMEs) responsible for gathering and negotiating electrical connections for all of the equipment.  There are also SMEs dedicated to gathering and negotiating software inputs and outputs.

During this phase, the development team needs to conduct numerous trade-off studies.  For example, what type of joint should be implemented between the wing and the fuselage?  Would it be a tension joint, shear joint, etc.?  Each solution has its pros and cons in terms of weight, manufacturability, and so on.  The chief engineer needs to make a decision with support from many teams.

Systems and Interior design continue to mature.  On the systems side, engineers continue to follow the rigorous system development process.  The diagram below illustrates the high-level process.  Engineers started the aircraft-level work and began to conduct the system-level work during the Conceptual Design phase.  In this phase, the team needs to refine system-level analyses, validate the aircraft-level work, and drill down to the item-level analyses. The Interior Team also has a tremendous amount of work to do.  We will go into more detail in the next article.

Figure 2. The system development process and its phases. Source: Wikipedia

Test

The test team needs to solidify their plans during the Preliminary design phase.  For instance, the team should have identified the test rigs required to support the program during the Conceptual Design Phase, as this information was necessary for the business case.  It now needs to collaborate with stakeholders, such as structures and systems teams, to refine the scope and the plans.

The cross-functional team must decide on the make-or-buy strategy for rigs.  The team also needs to identify sites for commissioning these rigs.  Depending on the lead time for facilities or equipment, the team may need to begin executing its plans during this phase.

Figure 3. Airbus A350 Iron Bird system test rig. Source: Airbus.

Manufacturing

The manufacturing team has work to do.  It supports the aircraft design, as illustrated in the example of the wing-fuselage joint.  It also has to refine the plan for the manufacturing site.  If it is a greenfield project (i.e., previously undeveloped land), the team may need to initiate some of the preparatory work.  Environmental assessment, site layout, building design, and obtaining permits are only a few examples.  Some of these activities have a very long lead times.

In addition to the site, the team needs to do work to prepare for production.  For instance, they begin to detail the production system, design tools/jigs/fixtures, etc.

Customer Support

The Customer Support team begins to ramp up during this phase.  It deploys experienced maintenance engineers and mechanics to support the design by providing valuable feedback on maintainability and accessibility.  For example, mechanics may work with engineering to move frequently serviced components closer to access panels.  They bring their own lessons learned to help improve the design.

Customer Support has a lot of planning to carry out if infrastructures like training, field support, and spares supply do not exist (e.g., start-ups).   It needs to create a business case for aftermarket products and services, if it hasn’t already done so.

Resources

Ramping up the team could be a challenge for companies of all sizes.  For mature OEMs, they typically move resources from one program to another.  This works when programs are well planned and executed.  If the previous program did not finish on time, external hires will be required to bridge this gap, or the new program needs to be launched at a later time.

For startups, their challenges are even greater.  All resources are essentially new hires.  The company also needs to make sure that there are sufficient resources to cover all functions and disciplines.  As illustrated in this series, an OEM needs more than engineering to execute a program. It must be able to cover all relevant areas.  Furthermore, would these new hires be full-time or part-time resources?  Would they be permanent employees, temporary contractors, or third-party consultants?

Sometimes, a resource is only needed on a part-time basis for this phase, but on a full-time basis starting the next phase.  If the company hires a contractor on a part-time, temporary basis, there is a risk of losing the knowledge when the contractor leaves at the end of this phase.  On the other hand, it is hard to justify a full-time person when they are doing part-time work, especially when there is a funding constraint.  A mature OEM, in this case, might have the opportunity to borrow a resource from another project to do the required work.

As described, a key challenge for an upstart is to ramp up the team in a productive manner.  Growing a team from a few dozen to hundreds of people is no trivial task.  Managers need time to write job descriptions, conduct interviews, and extend offers to candidates.  After a candidate accepts an offer, it may take them weeks, if not months, to show up for their first day.  Managers will then need to onboard this employee and provide training to ensure productivity.  If the company needs to hire a manager to build its team, this process will take even longer.

Since startups typically don’t have a lot of processes written or training materials produced, managers will either need to spend time generating these documents or providing on-the-job training.  Either way, they will need to divert valuable time from program execution to equally important human resources and training activities.  Start-ups should not underestimate the effort and coordination required to execute a proper ramp-up.

Speeding Up the Preliminary Design Phase

Emerging technologies, such as AI, may help offload some of the human resources activities from managers.  For example, it could generate job descriptions for various positions.  Since job descriptions are readily available in the public domain, AI would have a higher success rate than technical analyses, such as the example we reviewed in Part 8 of this series.  Managers will have to review and adjust these job descriptions, but this will certainly eliminate some bottlenecks.

Various project management techniques could also help manage a program better.  For instance, some methodologies encourage disclosure of challenges early rather than sweeping issues under the rug until it is too late.  Nonetheless, a program can only deploy this type of methodology successfully if the leadership team supports it by actions, not just by words.  Sometimes corporate culture changes are required to enable the implementation of these types of initiatives.

On the flip side, leaders need to be smart about speeding up this phase.  This phase creates a significant portion of the foundation for the program.  If the team decides to plow forward without having answers to key questions, identifying key risks, and developing appropriate mitigation plans, rework will be required.

As illustrated in Part 7 of this series, the cost of change increases exponentially after this phase.  A development program will pay heavy interest on technical debts.