Bjorn’s Corner: New aircraft technologies. Part 34. Design for Certification

October 13, 2023, ©. Leeham News: We are discussing the Detailed design phase of an airliner development program. We have discussed program management methods, development techniques, tools for Detailed design, that improved production methods are as important as improved technology, and that the interaction with the suppliers is key.

But another consideration that affects detail design is the influence of the Certification process. Certification has a major influence on the program work in every step of the aircraft program.


Figure 1. The online version of the FAA 14 CFR Part 25 Airliner Airworthiness regulations. Source: US CFR.


The design and later production and operation of a new airliner are influenced in a major way by the need to adhere to the certification rules of the country where it’s registered and operated. Each country has its own regulator at which the operator must seek authorization for the design, production, and operation of the aircraft.

In practice, we have a few leading regulators like the US FAA and EU EASA, on which local regulators are encouraged by ICAO to base their certification rules, with local adaptations. An airliner OEM must seek certification in each jurisdiction where it wants to sell and operate the aircraft.

As the achievement of global (FAA and/or EASA) and local certification is so important, a new airliner program is adapted to the certification process and its needs.

Here is a summary of what’s needed and must be done;

  • At the start of the project, during the preliminary design phase, the applicable certification rules must be researched for every part of the aircraft. If new technology is used that doesn’t have existing certification rules, a special condition is applied for, that shall achieve “equivalent safety.” The agreement with the regulator or regulators on applicable certification rules for the project is an important program milestone.
  • The next step is to agree on the “Means of Compliance, MoC.” It’s how the project shall demonstrate that it meets the certification rules. It can be by analysis, like the number and type of structural strength simulations needed for a certain part of the aircraft, or structural tests on test articles to verify conformity.
  • Once the applicable rules and means of compliance are agreed on, the project work is aligned to produce the evidence that has been agreed upon in means of compliance. For detail design, it governs what is done and how it’s done. It’s not sufficient to design a part to internal standards and documentation requirements; it must fulfill the certification requirements and generate the means of compliance data and reports needed.
  • Only when design and later testing have generated all the thousand reports defined in means of compliance can an aircraft project achieve design certification. As we talk about thousands of detailed analysis reports or tests, it’s understandable that the certification of a civil airliner is not a fast process. However, the process has generated an exceptionally high safety level for today’s airliners and their operation.

As the certification part of an airliner project is of critical importance, the OEMs establish special certification line organizations that maintain and develop the knowledge around certification in the jurisdictions where the company’s airliners are sold and operated. A new airliner program then creates its own certification organization that draws its personnel from the company’s line organization.

It’s not only the design certification that affects the airliner Detail design. If the designers want to use a novel technology like thermoplastic composites instead of the established thermoset method, it has to ensure that the method and its design and production rules and processes are mature enough so that they can be accepted by the regulator, not only for the OEM’s home jurisdiction but in every country it intends to sell and operate the aircraft.

I have several times discussed new and improved methods for the production of, for instance, carbon composite parts, only to be informed, “Yes, it’s all interesting and what we want to use, but we have not achieved acceptance for the design “allowables” (i.e., design rules), so this method can’t be used for the project.”

You could say, “Certification rules a project like nothing else.”

14 Comments on “Bjorn’s Corner: New aircraft technologies. Part 34. Design for Certification

  1. The aircraft manufacturer then references to all its design standards, materials properties standards, standard parts and process standards that need to be followed by themselves and all its suppliers as part of their way to control their design and its quality. Then comes all the other manuals the operator and Part-145 MRO shops needs to follow. Don’t even touch the software standards and electronics. In summary, it is massive.

  2. Bjorn,
    I have often heard that once a certification basis has been agreed with regulator(s), it is frozen for 5 years; passed this time it shall be re-discussed, ence motivating every OEM target to develop in this time frame.

    Do you (or any body else) confirm?

    • It is actually the date of application that freezes the requirements and then the applicant has 5 years from the date of application to get the transport category aircraft type certified (refer to 14 CFR 21.17). If the type certificate is not issued within 5 years of the application then approval of a longer period typically requires that the certification basis be updated to include later amendments.
      It should be emphasized that the certification basis may include special conditions, exemptions and equivalent level of safety findings which are project specific and therefore only get formalized after the application has been submitted.
      The applicant may elect to comply with later amendments; this can be convenient if type certification within the 5 years is in doubt or there will be derivatives for which the applicant will want to use the same certification basis.

  3. Sometimes, “certification rules a project like nothing else.” But not always. In the real world, certification engineers and other finders of compliance are subject to pressures from cost, delivery, and testing, just like anyone else.

    One way to shelter the internal certification organization from “undue influence,” is to move it outside the direct chain of command of the project.

    Leadership also matters.

    One key cultural factor is whether the program has a strong problem-solving culture with good lateral communication between product development, design, certification, and testing organizations. If negative information is seen as an opportunity to solve problems upstream, you will get better outcomes than you will from a culture that suppresses negative information.

    • Stan:

      Very well put. While I worked on the client side, working with contractors (assuming you could) was very critial to a good outcome.

      If both sides were knowledgeable and good relationships the outcome was vastly better.

      Mutual respect is truly important.

  4. Back when it was called the MH90 your departing leader really beat me up over this when I said they had ten years to certify. He said they had all the time they wanted because they were in Japan certifying to FAA rules. Several posters corrected me, saying that FAA limit was five years. Shortly thereafter the project was canceled and reborn as Spacejet/Spicejet etc.

  5. The 787 battery saga was an excellent example of how things could and did go terribly wrong.

    Boeing made a huge mistake (or stupidity in arrogance) when they decided to create their own standards that were a joke.

    The FAA should never have gone along with it.

    After the failures it was turned over to the Radio Technical Committee to come up with standards and they did a great job.

    The in depth report on the debacle is great reading from a how not to do it standpoint. Has a lot in common with the Maconda debacle.

    • “The FAA should never have gone along with it.”

      Lol. That’s the easiest path to follow. Was there any political will to give FAA the right budget to run?? Politicians: don’t stand in the way of innovators; let the (industry) experts decide; remove red tapes etc

    • Trans…
      I always thought the 787 battery was controlled by a Boeing SCD Drawing. The Specification Control Document defines what the deliverable is, but is very light on how to execute. It was Boeing sort of copying the FAA’s TSO (Technical Standard Order) process where the FAA designates what the component must do, but doesn’t define how to get there. FAA TSO-C173 applies to permanently installed batteries providing power for aircraft equipment including emergency and standby systems and electrical power to start aircraft engines or auxiliary power units and defines the performance and other characteristics the battery need’s to conform to, When the battery manufacturer was given the SCD drawing, it also was given the responsibility to get the FAA TSO approval. Boeing then installs the component as a yellow tagged item. RTCA DO293 was included in the TSO by reference, and its inclusion in the TSO predated the 787 fire. This was the section of the TSO that covered Metallic batteries as opposed to lead/acid chemistry. If Boeing erred here, and I’m not sure they did, it was in trying to mimic the FAA TSO process thru the use of its SCD system, As always, hindsight provides amazing clarity. Also remember that when the 787 program was stood up as the 787 division, Boeing was more interested in staffing it in Catia/Enovia operators out of allied industries than moving aircraft veteran managers from BCAC to lead the new program. Somebody in the C suite made a bad call on choosing computer wizards over airplane guys and the Tupperware Disaster wasn’t a big surprises to those of us who avoided it like the plague.

      • ‘the Tupperware Disaster wasn’t a big surprises to those of us who avoided it like the plague.’

        Is that what you guys called the 787 in-house? If it is, I am going to hijack the term now, when referring to the program…

        …(and blame the BA insider)

  6. You could say, “Certification rules a project like nothing else.”

    …and who rules the certificators?

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