Why AM Metal Parts Break Traditional Airworthiness Certification

Additively manufactured metal components cannot be certified under existing airworthiness clause structures because the material and the manufacturing process are inseparable — a fundamental incompatibility that invalidates the conventional approach of verifying material allowables and manufacturing method compliance independently. As documented by COMAC’s Beijing Institute of Civil Aviation Technology in their 2025 single-part airworthiness compliance verification patents, AM parts exhibit significant material anisotropy and structural non-uniformity that vary point-by-point within the structure as a function of build parameters.

This material-process coupling renders the conventional approach of independently verifying material allowables (e.g., clauses 23.603/25.603) and manufacturing method clauses (23.605/25.605) inapplicable. The same COMAC patents confirm that establishing material strength properties and design allowables through the conventional statistical coupon database approach would require an extraordinarily large number of test specimens to capture the spatially varying performance of AM parts — an approach that is not economically viable. According to EASA, special manufacturing processes require approved process specifications that guarantee consistent structural soundness, a bar that legacy coupon databases alone cannot meet for AM.

The qualification framework must therefore address surface roughness, internal porosity, residual stress, and microstructural heterogeneity simultaneously. Chinese airworthiness regulation CCAR-25 Article 605 — directly analogous to AS9100’s requirements for special processes — requires that manufacturing methods produce a consistently sound structure and that any process requiring strict control be executed per an approved process specification. This regulatory baseline applies to Western aerospace supply chain qualification contexts with equal force.

The University of Tennessee Research Foundation’s 2025 qualification method directly targets these challenges by combining predicted thermal signature forecasting, representative volume element (RVE)-level measurement of thermal-mechanical-chemical properties using in-situ and ex-situ sensors, and physics-based simulation to predict microstructural heterogeneity — enabling qualification of geometrically complex parts that would otherwise resist conventional test-based approaches.

Proof-Load Testing as a Substitute for Radiographic NDI in AS9100 AM Qualification

The rough surface finish of additively manufactured metal parts causes haze in radiographic X-ray images, making conventional non-destructive inspection unreliable for flight-critical AM components — and proof-load testing, patented by The Boeing Company across multiple jurisdictions, provides the technically viable alternative. The method involves calculating a deterministic proof load that, when applied to a part, will cause fracture if and only if an internal flaw of safety-critical threshold size is present.

“Because the proof load is defined as greater than the maximum fatigue load, any flaw large enough to initiate a fatigue crack will manifest as fracture under the proof load — providing a binary, pass/fail qualification result where radiography cannot.”

Boeing’s US patent filing from 2020 explicitly addresses the scenario of replacing a casting with an AM part in aerospace applications, where qualification for flight use is required. The Chinese counterpart filing provides a worked example involving a flap actuator housing — a flight-critical structural component previously produced as an aluminum casting and subjected to radiographic quality control. The EP filing confirms that the proof load is derived from fracture mechanics parameters: the ratio of fracture toughness to threshold stress intensity factor, scaled by part geometry and operational load direction.

Print orientation is a critical controlled variable in the proof-load framework. Because fracture toughness can vary with build direction in AM metal parts, the proof load magnitude and application direction must be specified relative to the print orientation. Boeing’s Chinese filing notes that if the load application angle changes significantly during routine service, the applied proof load may be insufficient to screen out flaws oriented toward untested load directions — a direct AS9100 risk management concern requiring documented build direction controls. The Indian filing extends the system architecture to include automated processor-based computation of allowable flaw geometry.

Certified Process Data Sets and In-Process Parameter Control for AS9100 Compliance

AS9100-compliant qualification of AM metal parts requires locking the process parameters that govern microstructure formation during the build — and Schubert Additive Solutions GmbH’s 2025 German patent establishes the most detailed public framework for doing so. The certified data set provided by a qualified supplier encapsulates three categories of parameters: plant-specific parameters (machine series, model, type, and manufacturer); component-specific parameters; and process-specific parameters including humidity, pressure, and temperature both external to and within the build chamber.

This tripartite lock on the build environment is directly aligned with AS9100 special process control requirements, which demand documented evidence that the process consistently produces the intended result. The importance of in-process monitoring is further addressed by Kobe Steel’s 2025 US and EP patents, which establish a defect dimension management protocol based on fracture mechanics: an allowable defect dimension is derived from the stress intensity factor limit value and the load stress variation range assumed in design. Any defect detected in the as-built object — or predicted from test specimen builds — is compared against this allowable dimension to determine conformance.

For wire-based AM methods applied to metal parts of unlimited size — relevant to large structural aerospace components — AML3D Limited’s 2021 Korean filing documents open-atmosphere solid free-form fabrication using consumable wire and electric arc processes, generating layer-by-layer models aligned with weld bead geometry. According to ISO standards for welding quality management, the control of bead geometry data constitutes a key traceability record under AS9100, as each layer’s deposition history must be traceable to the final mechanical property map of the part.

Iterative Qualification Loops and the AS9100 Audit Trail for AM Parts

COMAC’s Beijing Institute of Civil Aviation Technology has developed an iterative, multi-round verification architecture that is directly aligned with the AS9100 first-article qualification concept for AM parts — and uniquely suited to generating the documented audit trail that AS9100 Clause 8.5.1 demands for special processes. The qualification campaign is divided into sequential rounds of test-specimen verification followed by finished-part verification.

In each round: a new manufacturing plan (process parameter set) is defined; specimens are produced and tested against the verification plan; if the first preset condition (specimen-level acceptance criteria) is not met, a new manufacturing plan is generated and the specimen round repeats; once the specimen-level condition is met, finished parts are produced and verified; if the second preset condition (finished-part acceptance criteria) is not met, the process returns to the specimen stage. This architecture provides a documented audit trail of each manufacturing plan attempted, rejected, or approved — precisely what AS9100 Clause 8.5.1 requires for special processes.

The University of Tennessee Research Foundation’s qualification method complements this iterative architecture by adding predictive capability. Using RVE-level thermal, mechanical, and chemical characterisation — combining in-situ sensors placed adjacent to the build with ex-situ post-build measurements — it validates physics-based simulation models and forecasts microstructural heterogeneity before physical test articles are committed. In an AS9100 context, this creates a model-based qualification evidence package that can accompany design authority documentation, reducing the number of physical iteration cycles required. As NIST has noted in its AM standards roadmap, physics-based qualification evidence is increasingly recognised as a complement to physical testing for complex geometries.

The process standards establishment method by COMAC’s engine division adds the regulatory perspective from CCAR-33 — analogous to FAR Part 33 and EASA CS-E for engine certification — which requires that materials used have suitability and durability established on the basis of experience or test, and must conform to approved standards guaranteeing that strength and other design properties are achieved. This establishes the regulatory floor that any AS9100-compliant AM qualification programme must exceed, as confirmed by FAA guidance on additive manufacturing for aviation applications.

Key Patent Holders and the Strategic Shift in AM Qualification Approaches

The patent dataset — spanning approximately 30 sources across the US, EPO, Germany, China, South Korea, and India — reveals a clear concentration of flight-critical AM qualification intellectual property among five organisations, each pursuing a distinct technical approach that reflects their position in the aerospace supply chain.

The Boeing Company is the most prolific assignee in the dataset, holding active patents in the US, EP, IN, CN, and BR jurisdictions covering proof-load flaw detection for AM parts. Boeing’s approach is notable for being specifically designed to enable replacement of cast metal parts with AM equivalents in structural aerospace roles — a commercially significant capability given the cost and lead-time advantages of AM over casting for low-volume flight hardware.

COMAC’s Beijing Institute of Civil Aviation Technology holds two active CN patents (2025) focused on the single-part airworthiness compliance verification architecture — a regulatory-first approach that directly confronts the decoupled material/process assumption underlying existing airworthiness regulations. This positions COMAC as a standard-setter for AM qualification frameworks applicable to civil aircraft certification under both CCAR and, by analogy, FAR/EASA CS frameworks.

Kobe Steel (Kabushiki Kaisha Kobe Seiko Sho) appears with two pending patents (US and EP, 2025) on fracture-mechanics-based quality management for AM objects, representing a supplier-side approach to generating the objective quality evidence required by AS9100 customer flow-down requirements. University of Tennessee Research Foundation holds a pending US patent (2025) on sensor-fusion and simulation-based metallic AM qualification, targeting complex geometries. Schubert Additive Solutions GmbH holds an active DE patent (2025) on the certified data set architecture for locking process and machine parameters as a qualification artefact.

“The overall trend is a shift from purely empirical coupon-based qualification toward hybrid physics-simulation plus in-situ sensor plus proof-test architectures — driven by the economic infeasibility of purely statistical material allowable databases for AM parts.”

This shift is driven by two compounding pressures: the economic infeasibility of purely statistical material allowable databases for AM parts (which would require an extraordinarily large number of test specimens), and the technical infeasibility of conventional radiographic NDI for AM metal surface conditions. According to WIPO‘s global innovation indicators, aerospace manufacturing consistently ranks among the highest-intensity sectors for quality management and process certification patent activity — a trend this dataset confirms is accelerating specifically around AM qualification methods.

The convergence of these five organisations’ approaches — proof-load testing, certified data sets, fracture-mechanics defect management, sensor-fusion simulation, and iterative compliance loops — maps directly onto the five pillars of AS9100’s special process control requirements. Together they constitute an emerging de facto qualification framework that, while not yet codified in a single standard, is being built patent-by-patent into the aerospace manufacturing supply chain. For IP professionals and R&D leaders monitoring this space, PatSnap’s IP intelligence platform provides real-time visibility into these filing activities across all relevant jurisdictions.