NADCAP Explained

In aerospace and defense manufacturing, many of the most critical steps are special processes: operations where the quality of the outcome cannot be fully verified by later inspection without destructive testing, or where inspection alone cannot guarantee conformance. Heat treat, Hot Isostatic Pressing (HIP), welding, chemical processing, coatings, and many forms of NDE fall into this category. That is why primes and major Tier 1s routinely specify Nadcap accreditation (commonly called “NADCAP” in industry) as a gating requirement for production sourcing—especially when parts will fly, carry load, or support mission-critical systems.

This article explains what Nadcap is (and isn’t), the special processes typically covered, why primes require it, how it changes quality risk, how to read a supplier’s scope correctly, and the RFQ language buyers actually use. It also ties Nadcap into real workflows used by successful organizations building hardware with additive manufacturing (AM), powder bed fusion (PBF) such as DMLS / SLM, PM-HIP, CNC machining, and controlled inspection and documentation under AS9100 and related defense/aerospace requirements.

What NADCAP is and what it isn’t

What it is: Nadcap is an industry-managed accreditation program for special processes and products, administered by the Performance Review Institute (PRI). It is not simply a paper exercise; it is a process control audit against detailed checklists developed and maintained by subscribing aerospace and defense companies (the “primes”) along with subject-matter experts. The focus is on how you run the process: parameter control, calibration, operator qualification, equipment maintenance, documentation, and the objective evidence that proves repeatability.

What it isn’t: Nadcap is not a general quality management system certification like AS9100 or ISO 9001. A supplier can be AS9100 certified and still be unacceptable for special processes if they lack Nadcap accreditation where required. Nadcap is also not a product certification, a design approval, or a guarantee that every part will be perfect. It does not replace engineering requirements, customer specifications, or first article inspection (FAI) per AS9102. It also does not automatically cover adjacent steps (for example, Nadcap accreditation for heat treat does not inherently qualify a supplier for NDE, machining, or additive manufacturing).

In practice, procurement and engineering teams use Nadcap as a risk-control mechanism: it provides a common, high-bar audit baseline for special processes that have historically driven escapes, latent defects, and high-cost investigations.

Which processes are typically accredited

Nadcap accreditation is process-specific and often sub-scope-specific (by material family, method, equipment type, and sometimes product form). A supplier may be “Nadcap accredited” for one process while being completely unaccredited for another. The following special process families are frequently relevant to aerospace, defense, and advanced manufacturing supply chains:

Heat treating: Vacuum heat treat, inert atmosphere heat treat, solution/age for precipitation-hardened alloys, and other controlled thermal cycles. For AM hardware, heat treatment is often used for stress relief, microstructure tuning, and property stabilization prior to machining and inspection.

Hot Isostatic Pressing (HIP) and densification-related processing: HIP is commonly used to close internal porosity and improve fatigue performance in castings and in PBF-built components. In PM-HIP (powder metallurgy + HIP), the HIP cycle is the primary densification step and is therefore central to part integrity. HIP is a classic “special process” because internal consolidation quality cannot be fully verified by simple dimensional checks.

Non-destructive testing (NDE/NDT): Penetrant testing (PT), magnetic particle testing (MT), ultrasonic testing (UT), radiographic testing (RT), and related methods. For additive manufacturing, CT scanning is increasingly used for internal feature verification and defect detection; it may be covered via specific NDE scopes depending on method and customer requirements. Nadcap places strong emphasis on procedure compliance, technician qualification, equipment calibration, sensitivity checks, and record retention.

Chemical processing: Cleaning, etching, passivation, anodize, conversion coatings, and other treatments that significantly affect surface condition, corrosion performance, and bonding/coating adhesion. These processes are sensitive to bath chemistry, contamination control, and time/temperature parameters.

Coatings: Thermal spray (e.g., HVOF), plating, and other coating processes. Coating performance is often strongly dependent on surface prep, process controls, thickness verification, adhesion testing, and post-process treatments.

Welding and joining: Fusion welding and other joining methods where the resulting metallurgical condition and defect population cannot be fully verified by simple visual inspection.

Material testing laboratories: Mechanical testing, metallography, chemistry, and related lab services. For qualification programs (including AM parameter development), test lab controls and traceability are critical.

Composites and other special process categories: Depending on the program, composites processing, sealants, and additional categories may be invoked.

Machining (including CNC and 5-axis machining), CMM inspection, and general assembly are typically controlled under the organization’s quality management system (e.g., AS9100) rather than Nadcap—unless a customer flows down a special, program-specific accreditation requirement. In real aerospace supply chains, Nadcap and AS9100 are commonly paired: AS9100 establishes the system baseline, and Nadcap governs specific special processes where escapes are most costly.

Why primes require it

Primes require Nadcap accreditation because it reduces variability and provides a standardized, industry-accepted level of confidence in special process execution. From the prime’s perspective, special processes represent a disproportionate share of risk: latent defects can pass incoming inspection, survive machining, and only show up in service as fatigue cracking, corrosion initiation, bond failure, or other mission-impacting issues.

Three practical reasons Nadcap shows up in purchase orders and sourcing approvals:

1) Special processes are not fully verifiable by inspection. You can measure dimensions with a CMM and verify geometry, but you cannot “CMM” a flawed heat treat, an improperly controlled HIP cycle, or a penetrant process with expired materials. Because verification is incomplete, process control becomes the product. Nadcap is designed to audit that control.

2) It streamlines supplier qualification and oversight. Without Nadcap, each prime would need to maintain deep audit capability for every special process across thousands of suppliers. Nadcap provides a common audit framework and shared oversight, allowing primes to rely on accredited suppliers while focusing internal resources on program-specific technical risks.

3) It supports regulatory and contractual compliance flows. While Nadcap is not itself a government regulation, many defense and aerospace contracts require robust supplier control, traceability, and objective evidence. Nadcap fits into that ecosystem alongside AS9100, ITAR controls (where applicable), DFARS-related obligations, and customer-specific quality clauses.

For additive manufacturing programs, primes are also trying to control a newer risk profile: build-to-build variability, powder control, post-processing effects, and inspection methodology maturity. When AM parts move from prototype to production, the supply chain often tightens around accredited special processes (HIP, heat treat, NDE, coatings) to reduce uncertainty—even if the AM process itself is controlled through internal qualification, customer audits, and documented process parameters rather than Nadcap.

How NADCAP affects quality risk

Nadcap affects quality risk by forcing discipline around the parts of manufacturing that are most likely to create latent nonconformities. It does this through detailed checklist requirements and “objective evidence” expectations: documented procedures, controlled parameters, calibrated instrumentation, trained personnel, and records that prove each job met requirements.

To make this practical, consider a common advanced manufacturing flow: PBF (DMLS/SLM) + HIP + heat treat + 5-axis machining + NDE + final inspection.

Step 1: Material control and traceability begin before a build. Even though Nadcap is not an AM accreditation, primes expect aerospace-grade traceability: powder lot/batch documentation, material specifications, storage controls, and contamination controls. These records ultimately support the Certificates of Conformance (CoC) and certification pack that accompany the shipped hardware.

Step 2: Post-build handling and special process planning. After the PBF build, parts may undergo stress relief, support removal, surface conditioning, and preparation for HIP. A high-performing supplier plans this as a controlled route, not a series of ad hoc steps. Travelers (routers) identify each operation, the applicable spec, acceptance criteria, and hold points.

Step 3: HIP as a risk reducer—if controlled correctly. HIP can significantly improve fatigue performance by reducing internal porosity, but only when parameters (temperature, pressure, soak time, ramp rates, atmosphere, thermocouple placement/verification, load configuration) are controlled and recorded. Nadcap expectations in special processes generally push suppliers toward rigorous recordkeeping: cycle charts, equipment calibration status, load diagrams, part identification through the furnace/HIP cycle, and clear links to the job traveler.

Step 4: Heat treat and microstructure control. Whether the intent is stress relief, solution and age, anneal, or another cycle, the risk is the same: an uncontrolled thermal history creates unacceptable properties. Nadcap-driven controls commonly include furnace uniformity and calibration discipline, instrument calibration traceability, documented procedures, defined quench media controls (when applicable), and verification that processing met spec requirements.

Step 5: NDE/NDT provides verification, but it is also a special process. Many quality escapes come from NDE method misuse: wrong technique, wrong sensitivity, expired consumables, incomplete coverage, or unqualified personnel. Nadcap expectations drive repeatability: procedure adherence, technician qualification records, equipment performance checks, and complete reporting. For AM parts with internal channels or complex lattices, CT scanning can be a powerful complement—when resolution, artifact control, and acceptance criteria are clearly defined.

Step 6: Machining and dimensional inspection close the loop. CNC and 5-axis machining turn near-net parts into final geometry; CMM inspection verifies dimensions. These steps are often where nonconformances are detected, but they cannot “fix” an upstream special process defect. Nadcap’s main risk-reduction value is upstream: it reduces the odds that a part reaches machining with an invisible metallurgical defect.

Step 7: The certification pack becomes part of deliverable quality. Aerospace buyers frequently evaluate suppliers on the quality of documentation: material certs, process certifications, NDE reports, calibration references, inspection results, and the final CoC. Nadcap-accredited suppliers tend to have stronger documentation discipline because audits demand objective evidence and record control.

Another risk angle is supplier-to-supplier consistency. When a program uses multiple approved special processors (e.g., two HIP houses), Nadcap helps reduce variation between them. It does not eliminate all variation, but it enforces baseline controls that make process capability more predictable and corrective actions more robust.

How to interpret a supplier’s scope

One of the most common sourcing mistakes is treating Nadcap as a binary attribute: “They have it” vs. “They don’t.” Engineering and procurement teams should instead read Nadcap like a technical capability statement: Does the supplier have the right accreditation, for the right process, on the right equipment, for the right materials, and in date?

When reviewing a supplier’s Nadcap status, focus on the following:

Accredited process family and method. “Nadcap accredited” must tie to the process you are buying: heat treat is not HIP; penetrant testing is not ultrasonic; chemical processing is not coating. If you are buying PM-HIP hardware, the HIP step is central—verify the HIP accreditation aligns with your material system and part class.

Scope details by material and technique. Many scopes are limited. For example, a heat treater may be accredited for certain alloy families or furnace types. An NDE provider may be accredited for specific methods and technique sheets. A coating provider may have limitations on coating types, materials, or part size. Do not assume your part fits their accredited envelope.

Equipment and location. Accreditation typically applies to a specific facility and defined equipment set. If a supplier quotes work “at another location” or “on a different furnace/HIP vessel,” that can be a red flag unless those assets are included in the accredited scope.

Expiration and audit cadence. Nadcap accreditations have validity periods and are maintained via periodic audits. Confirm the accreditation is current through the planned production window—not just current on the day of RFQ.

Objective evidence maturity. Even with accreditation, strong suppliers can quickly provide the evidence buyers need: certification packs, sample travelers, redacted cycle charts, calibration summaries, and a clear explanation of how they control job identification through the process. Weak suppliers often struggle here, which becomes a schedule and risk problem during PPAP-like readiness activities, FAI, or source inspection.

How it interfaces with AS9100 and program clauses. Nadcap does not replace AS9100. Buyers should confirm both: the supplier’s QMS (AS9100) and the special process accreditation(s) relevant to the part. For defense programs, also ensure the supplier can support controlled technical data handling (ITAR where applicable), required material traceability, and DFARS-related flowdowns if they appear on the contract.

Procurement teams should treat scope review as a collaborative check with engineering and quality. If a drawing calls out a specific spec revision for heat treat or NDE, verify the supplier’s accredited procedures and capability match that requirement before award.

RFQ language buyers use

Buyers and program teams typically encode Nadcap requirements directly into RFQs and purchase orders with clear flowdowns. The goal is to prevent ambiguity later (during FAI, source inspection, or receiving). Below are common, practical patterns—written in the style often seen in aerospace/defense sourcing documents. These examples should be tailored to your program’s specifications, part criticality, and customer clauses.

Accreditation gating requirement: “Supplier shall maintain Nadcap accreditation for all special processes performed, as applicable to this RFQ/PO. Accreditation shall be current at time of processing and shipment. Sub-tier special processors shall also be Nadcap accredited for the applicable process.”

Process-specific scope callout (heat treat): “Heat treatment shall be performed by a Nadcap-accredited heat treat facility within an approved scope for the specified alloy and process type. Supplier shall provide furnace charts/cycle records, quench media records (if applicable), and a Certificate of Conformance referencing the applicable specification and revision.”

Process-specific scope callout (HIP / PM-HIP): “HIP densification shall be performed by a Nadcap-accredited facility. Supplier shall provide HIP cycle records (time/temperature/pressure), load identification, and traceability from part serial/lot to HIP run. For PM-HIP components, supplier shall maintain traceability from powder lot through HIP consolidation and subsequent post-processing.”

NDE callout with reporting expectations: “NDE shall be performed by a Nadcap-accredited NDT facility for the specified method(s) (PT/MT/UT/RT/CT as applicable). Reports shall include procedure/technique identification, acceptance criteria, inspector identification/qualification, equipment identification, and results traceable to part serial/lot.”

Sub-tier control language: “If supplier subcontracts any special process, supplier remains responsible for compliance to all flowed-down requirements, including Nadcap accreditation, record retention, and delivery of complete certification packages.”

Certification package definition (what engineering and receiving actually need): “A complete certification pack is required with shipment and shall include: material certifications (heat/lot), process certifications (HIP/heat treat/coating/NDE as applicable), inspection results (CMM/FAI when required), and a final CoC. Records shall be traceable to part number, revision, lot/serial, and purchase order.”

AM + post-processing integration language: “For additively manufactured hardware (PBF/DMLS/SLM), supplier shall document build identification, powder lot traceability, post-processing route (including HIP and heat treat), and inspection plan. Any special process steps shall be performed by Nadcap-accredited sources when required by customer or drawing.”

Right-to-audit and quality escape response: “Supplier shall notify buyer within 24 hours of any suspected special process nonconformance impacting delivered product. Supplier shall support root cause and corrective action, provide objective evidence, and make records available for review. Buyer reserves right of access to applicable records and facilities, including sub-tier special processors.”

From a practical standpoint, strong RFQs also define what “acceptable evidence” looks like. If your receiving inspection expects furnace charts, specify that up front. If your program requires source inspection or government witness, define hold points early. These are not just administrative details; they directly affect schedule, cost, and the probability of late-stage surprises.

Finally, Nadcap requirements should be aligned with part criticality. Over-specifying accreditation for low-risk hardware can inflate cost and constrain supply. Under-specifying for critical hardware can create program-threatening escapes. The best organizations calibrate Nadcap flowdowns to the technical risk profile of the part and the maturity of the supply chain—especially when new technologies like additive manufacturing and PM-HIP are involved.