Defining Performance Requirements & the Case for Test and Computation

This is Part 2 of a three-part series documenting Ergoseal's FAA Parts Manufacturer Approval process in real time. Part 1 — Inside the Process of Qualifying Aircraft Seals for FAA Approval — covered what PMA is, why qualifying aircraft seals is particularly complex, and why Ergoseal is pursuing the test-and-computation path.

In Part 1 of this series, we outlined the foundation of the FAA PMA process: what approval actually requires, why these seals are more complex to qualify than most people expect, and how we approached the initial phase of reverse-engineering to establish design intent. We also explained why, for this program, testing and computation are the right path.

This installment picks up where that work leaves off — into the phase where design intent becomes engineering requirements, and early analysis and testing begin to shape the validation strategy.

In This Blog:

• From Design Intent to Defined Requirements
• What We Are Defining and Why
• Early Analysis: Building the Engineering Foundation
• Why the Test and Computation Path Requires This Level of Rigor
• What Comes Next

This is where the work gets specific.

From Design Intent to Defined Requirements

Establishing design intent, as we described in Part 1, is about understanding how the seal functions within its system. But understanding is not the same as specification. Before any formal validation can begin, that understanding has to be translated into defined, measurable performance requirements.

For a replacement aircraft seal pursued under test and computation, those requirements have to be derived independently. There are no OEM specifications to work from. Every requirement — temperature range, pressure limits, fluid compatibility, compression set, dynamic performance — has to be established through engineering analysis of the existing certified part and the system environment in which it operates.

This is not a simple reverse-lookup. It requires disciplined judgment about which characteristics are critical to airworthiness and how each one should be defined and tested. Get it wrong at this stage, and you're either over-specifying in ways that make validation unnecessarily difficult or under-specifying in ways that leave real performance risks unaddressed.

Ryan Neris, Ergoseal Design Engineer, describes what that discipline actually requires in practice:

"Defining performance requirements without OEM data demands strong engineering judgment, use of first principles, benchmarking, and conservative assumptions to fill in gaps. It requires careful validation, clear documentation of assumptions, and cross-disciplinary review to avoid blind spots. If done carelessly, the risks include under- or over-design, safety issues, poor system integration, cost overruns, and failures that may only appear late in development."

With those risks clearly defined, the next step is determining exactly what needs to be specified — and why each requirement matters to airworthiness.

What We Are Defining and Why

For the seal program currently underway at Ergoseal, the requirements definition phase focuses on several interconnected areas.

• Temperature performance. Aircraft seals operate across extreme ranges — from subzero conditions at altitude to high temperatures in system operation. Understanding the thermal envelope this seal must function within is foundational to material selection and validation planning.
• Pressure cycling behavior. Seals in active aircraft systems don't hold a static load. They cycle — sometimes thousands of times over a service life. Compression set resistance and long-term sealing integrity under repeated pressure changes are critical characteristics that have to be defined early and validated thoroughly.
• Fluid compatibility. The seal's chemical environment determines material viability. Fluid exposure requirements are being established based on the system this seal operates in, including both primary fluids and any incidental chemical exposure that could degrade performance over time.
• Dimensional and interface requirements. How the seal fits, compresses, and interfaces with surrounding hardware is as important as the material itself. Tolerances, compression rates, and installation conditions are being defined to ensure that the validated design will perform correctly in its installed state.

Neris cites dimensional tolerancing as a requirement that typically requires special attention:

“The priority is always safety, starting with defining acceptable limits within which proper fit, form, and function are controlled and assured. Subsequently, care must be taken to avoid excessively constraining the dimensional tolerances and thereby over-designing the part. Otherwise, the manufacturing process can needlessly introduce waste and result in unnecessary cost and/or lead time overrun, which undermine the value of a purpose-built solution. This process involves a multi-faceted approach incorporating validated internal design guidelines, industry standards, technical documentation review, end-use application data, precise in-house manufacturing and metrology, and diligent conformance to FAA-PMA requirements.”

With requirements taking shape across each of these areas, the next phase shifts from definition to action — and that means early analysis work begins.

Early Analysis: Building the Engineering Foundation

The early analysis phase is not yet formal testing for FAA submission — it is the engineering groundwork that makes eventual testing meaningful.

"In-house expertise in the design and manufacturing of the same product line categories allows early through final analysis work to be efficient and comprehensive," says Neris. "In addition to detailed dimensional and material characterization, nuances in fit and finish are identified for best-fit manufacturing, inspection, and special process methods. Part requirements are carefully specified for not only design function but also reliable manufacture and inspection. The early analysis work sets up the process for success by asking the right questions, gathering all available facts, and ensuring the foundation for execution is firm and valid."

This is a phase that is easy to underestimate from the outside. Early analysis doesn't produce a test report or a compliance matrix. What it produces is confidence — confidence that the requirements are correctly defined, that the design approach is sound, and that the formal validation program being built will demonstrate what it needs to demonstrate.

Skipping or compressing this phase is one of the ways PMA programs run into trouble later. If the requirements aren't right, the testing doesn't prove what you think it proves. If the engineering foundation isn't solid, FAA review will surface the gaps.

Why the Test and Computation Path Requires This Level of Rigor

It's worth being direct about what distinguishes test and computation from other PMA approval paths, and why the front-end work matters so much.

Under identicality — the other primary PMA path — an applicant demonstrates that their replacement part matches the OEM's certified design in every material respect, using the OEM's own design data under a licensing agreement. The design has already been validated through the original certification. The applicant's job is to prove manufacturing equivalence.

Under test and computation, there is no licensed design to reference. Ergoseal is developing its own approved design data from the ground up. That means every performance claim has to be supported by independent engineering analysis and testing. The FAA will review not just the test results, but the basis for the requirements and the rigor of the methodology.

This is a more demanding path. It is also, for programs where OEM data is not accessible, the only path that leads to a legitimate, fully documented approval.

"Building an approved design package from the ground up means fully defining the part through controlled engineering data — requirements, drawings, material specs, analyses, testing, and traceability — so it can be certified and consistently reproduced. It requires rigorous validation, documentation, and configuration control to demonstrate the part will perform safely and reliably in service. That level of rigor matters to aerospace engineers and MRO teams because it reduces uncertainty, ensures regulatory compliance, and gives confidence that the part will integrate properly, last as expected, and not introduce risk into critical systems," says Neris.

That foundation — built requirement by requirement, analysis by analysis — is exactly what the next phase of this program is designed to validate.

What Comes Next

The work in this phase — requirements definition, early analysis, and engineering documentation — is not visible in a finished part or a published approval. But it is the foundation that everything else is built on. When formal testing begins, it will be testing against requirements that have been carefully derived and clearly documented. When the FAA reviews the submission, the engineering basis will be traceable back to this phase.

In Part 3, we'll cover how that formal validation comes together: the testing program, the documentation package, and what the FAA review process looks like for a replacement aircraft seal. We'll also share what we've learned about what separates a PMA submission that moves smoothly through review from one that doesn't.

Questions about PMA seal sourcing or what approval really requires for your program? Contact the Ergoseal engineering team.

About this series: Ergoseal is documenting our FAA PMA process in real time. This three-part series provides aerospace engineers, MROs, and program managers with practical insight into what it takes to qualify a replacement aircraft seal for FAA approval — and why that level of rigor matters to program reliability and supply chain resilience.