Certification does not begin when the part is finished. It begins when the first design decision is made. Engineers who treat FAA AC 20-107B, EASA CS-23/CS-25, or customer-specific DDP requirements as a final checklist rather than a design input create rework cycles that are expensive, slow, and largely preventable. The composite structures that reach certification on schedule are the ones where compliance thinking was embedded from concept through production.

A note on scope: as a Built-to-Print supplier without Design Organisation Approval (DOA) or Production Organisation Approval (POA), COTESA does not hold or share the certification basis for a program. That responsibility remains fully with the OEM’s design organisation. What COTESA contributes is the process data, traceability, and manufacturing evidence the OEM’s DOA depends on to substantiate that basis — and the earlier that contribution starts, the fewer surprises the OEM’s certification program encounters downstream.

Why Does Certification Thinking Have to Start at the Concept Phase?

The short answer: because every structural decision downstream locks in the evidence requirements upstream.

Under FAA Advisory Circular AC 20-107B and the equivalent EASA Composite Material Fabrication Approval framework, certification of a composite structure requires a “building block” approach. That means coupon-level tests inform element tests, element tests inform sub-component tests, and sub-component tests inform full-scale structural validation. If your fiber orientation, ply schedule, or joint geometry changes midway through development, a substantial portion of that test pyramid must be rebuilt.

What the Building Block Approach Actually Demands

The building block approach, as defined in CMH-17 (Composite Materials Handbook, Volume 3), requires that material allowables be established at the coupon level under the full range of environmental conditions the structure will see in service: temperature, moisture absorption, and combined loading. B-basis allowables, which provide a statistical floor that 90% of test population values will exceed at 95% confidence, are the standard for primary structure. A-basis values apply where a single failure path would be catastrophic.

If the design intent changes after allowables testing is complete, the allowables may no longer be applicable. That is not a paperwork problem. It is a test program restart.

How Early Supplier Alignment Protects the Concept Phase

OEM engineering teams frequently develop composite structure concepts in isolation and bring suppliers in at detail design. This is a pattern that consistently produces surprises. A supplier manufacturing complex CFRP assemblies at production scale carries process knowledge about cure cycle sensitivity, tooling-induced residual stresses, and ply drop behavior that belongs in the concept conversation, not the design review.

Manufacturability constraints are design inputs that the OEM’s certification basis depends on — not production footnotes to be resolved later. A laminate that can only be produced consistently within a narrow autoclave cure window has narrower process latitude. Narrower process latitude means tighter Special Process Specifications (SPS) and more stringent incoming material qualification under BMS (Boeing Material Specifications) or equivalent OEM standards.

What Are the Most Common Structural Challenges in Certified Composite Assemblies?

Three categories account for the majority of certification delays in composite structural programs: load path discontinuities, joint validation complexity, and barely visible impact damage (BVID) substantiation.

Load Path Discontinuities at Joints and Transitions

Carbon fiber composites carry load efficiently in the fiber direction and comparatively poorly out-of-plane. Where load paths transfer between composite members, or between composite and metallic structure, the out-of-plane loading component becomes the design driver. Fastened joints in CFRP introduce bearing and bypass loads that must be substantiated through tests under CS-25.305 (ultimate loads) and demonstrated through fatigue analysis consistent with the aircraft damage tolerance requirements of CS-25.571.

Bolted joints in carbon fiber also require careful attention to galvanic compatibility. Direct contact between carbon fiber and aluminum under wet conditions creates a galvanic couple that accelerates corrosion in the metallic component. Composite-to-titanium joints, though heavier, are the common solution for primary structure interfaces.

Why Fastener Hole Quality Drives More Certification Risk Than Most Programs Anticipate

Hole quality in CFRP is a function of drill bit geometry, feed rate, spindle speed, and backup material. Delamination at exit holes is a documented failure mode under FAA DER review. NADCAP-accredited special processes for drilling and fastener installation exist precisely because this is a repeatable source of structural degradation that is largely invisible to visual inspection. Ultrasonic C-scan inspection per ASTM E2700 is the standard method for detecting delamination in the laminate surrounding fastener holes in primary structure.

BVID: The Damage Tolerance Requirement That Surprises Programs Late

AC 20-107B requires that primary composite structures demonstrate residual strength after BVID, defined as the damage produced by an impact with sufficient energy to cause damage that is not reliably detectable by scheduled inspection methods. The threshold is typically established at 6.7 J (60 in-lb), though OEM structural substantiation documents may use higher values depending on skin thickness and accessibility.

The residual strength requirement after BVID is that the structure must sustain limit load, not ultimate load. That distinction matters. It means the certification basis allows some degradation, but that degradation must be characterized through tests, documented in the structural repair manual (SRM), and tied to inspection intervals in the maintenance planning document (MPD).

Programs that do not account for BVID test article requirements in their schedule routinely discover this gap at the CDR stage. Test article lead time plus test execution plus data reduction is typically 9 to 14 months. It is not a parallel path with design work.

How Do You Manage Tolerances and Quality Assurance for Certification Credit?

Composite part tolerances carry certification implications that metallic tolerances do not. In metals, a dimensional deviation from nominal is primarily a fit and function issue. In composites, it can also be a material property issue.

Cure Cycle Traceability and Its Role in Certification Documentation

Every primary composite structure part produced for a certified aircraft must be accompanied by traceability data linking the physical part to its cure cycle records. The cure cycle records must demonstrate that the time-temperature profile remained within the bounds of the qualified process specification throughout the cure. Autoclave or oven chart data, thermocouple placement records, and vacuum bag integrity data are all retained as objective evidence.

Under EN 9100:2018, which COTESA holds, the quality management system framework requires this traceability as a baseline. The certification authority, whether FAA, EASA, or a delegated DER, will ask for it during conformity inspection. Parts without adequate cure traceability cannot be installed on a certificated aircraft, regardless of their dimensional and mechanical compliance.

NDT as a Production Conformance Tool, Not a Defect Sorter

Non-destructive testing in composite production is sometimes treated as a final filter that catches bad parts before shipment. That is the wrong model. Ultrasonic inspection per ASTM E664 or pulse-echo methods qualified under the OEM’s NDT process specification is a conformance verification against the allowable defect limits defined in the engineering drawing. Those limits are linked back to the building block test program.

If the NDT program is not calibrated to the defect sizes that were accounted for in the structural allowables, the NDT results do not provide the certification credit they appear to. The alignment between design-allowable defect size and NDT detection threshold must be documented and maintained across all production tooling changes.

Does Early Supplier Collaboration Actually Reduce Program Risk, or Is That Just a Sales Pitch?

This is a fair objection. The claim that suppliers should be involved earlier is made frequently and often without specifics. Here is what the data and documented industry patterns actually show.

Objection 1: “We don’t have enough design detail to involve suppliers at the concept phase.”

The misconception here is that suppliers need a completed design to contribute. They do not. What concept-phase collaboration requires is a statement of the structural envelope: load magnitudes, operating temperature range, material family, and manufacturing method candidates. From that, a supplier with NADCAP composites accreditation and an ISO/IEC 17025-accredited material testing laboratory can provide process capability data and flag constraints before they become drawing requirements.

The value is not design input in the certification sense. It is risk input. Knowing at concept phase that a particular ply schedule requires a cure temperature that exceeds what your autoclave can hold uniformly across a large tool is actionable. Knowing it in the first article is not.

Objection 2: “Supplier process qualification takes too long to start early.”

Supplier qualification under AS9100 and NADCAP does take time. But the timeline is predictable and can run parallel to early design development if started when the material and process selection is made, not after design freeze. Programs that wait for design freeze before initiating supplier qualification consistently slip their first article inspection dates by 6 to 12 months.

Customer-specific approvals, including Airbus SQIP and Boeing D6-82479 supplier quality requirements, have defined documentation packages. Starting that documentation early, against a preliminary material and process specification, compresses the qualification timeline at the back end.

Objection 3: “We’ll handle certification compliance internally.”

OEM engineering teams are accountable for the certification basis and the means of compliance — that responsibility is not, and cannot be, delegated to a Built-to-Print supplier without DOA or POA. That division of responsibility is exactly the point. The compliance evidence the OEM’s certification basis relies on is built from supplier process data, material traceability records, and NDT conformance documentation. A supplier that does not understand the certification requirements embedded in the drawing notes and SPS references cannot reliably produce that evidence. Handling compliance internally does not eliminate the supplier’s role in generating the underlying evidence. It just makes the interface between OEM and supplier less deliberate — which is where documentation gaps and late-stage surprises tend to originate.

What Does a Certification-Ready Manufacturing Posture Actually Look Like in Practice?

The operational difference between a supplier that accelerates certification and one that complicates it comes down to three things: process discipline, documentation architecture, and how NDT findings are handled in real time.

Process discipline means that the special processes applied to primary structure, layup, cure, bonding, and fastener installation, are performed to a written and qualified SPS that has been reviewed and accepted by the OEM’s quality organization. Any deviation from the SPS during production triggers a nonconformance record and an engineering disposition. There are no informal workarounds.

Documentation architecture means that the part traveler, cure records, material certification, and NDT report are linked by part serial number and retrievable as a package. This is not optional for certificated parts. It is the difference between a part that can be installed and a part that cannot.

NDT findings in production are not inherently disqualifying. Composites produced to aerospace tolerances regularly contain porosity, minor delaminations, and other indications that fall within drawing limits. The question is whether the finding was properly characterized, compared against the applicable accept/reject criteria, and documented with the disposition rationale. A supplier whose NDT process generates clean documentation on indications that are within limits is more valuable to a certification program than one who ships parts with no findings and no records.

Talk to an Engineer

Certification in composite structures is not a phase. It is a design condition that runs from concept to delivery. Engineers who embed compliance thinking early, who align their supplier relationships around process qualification and documentation architecture, and who treat the building block test program as a design constraint rather than a downstream obligation, are the ones whose programs reach certification on schedule.

COTESA supports aerospace programs from early development through serial production, with NADCAP Composites Merit Status, NADCAP Non-Destructive Testing accreditation, and an ISO/IEC 17025-accredited material testing laboratory. If your program is in early development or approaching a supplier qualification decision, talk to the COTESA engineering team about how we structure production and documentation to support your certification path.