🔥 NADCAP
NADCAP and Milling: Where Special-Process Accreditation Meets Machined Parts
Here is the honest truth most directories will not tell you: NADCAP does not have a milling accreditation, because milling is not one of the special processes NADCAP was created to govern. The pairing matters anyway, because nearly every milled aerospace part passes through NADCAP-accredited operations before and after the cutter touches it. This page explains the real relationship between machining and NADCAP, and how a buyer should use it.
NADCAPAS9100ISO 9001
Why milling itself is not a NADCAP commodity
NADCAP, the National Aerospace and Defense Contractors Accreditation Program, is administered by the Performance Review Institute (PRI) on behalf of the prime contractors who form its industry-managed governance. It accredits special processes, defined as processes whose results cannot be fully verified by subsequent inspection of the product and whose proper outcome depends on tight control of the process itself. The NADCAP commodities include Heat Treating, Chemical Processing (anodize, chem film, passivation, plating), Coatings, Nondestructive Testing, Welding, Surface Enhancement (shot peen), Materials Testing Laboratories, Composites, and more.
Milling is conspicuously absent from that list, and for a defensible reason. A milled feature can be fully verified after the fact: you measure the dimension, the profile, the position, the surface finish, and you know whether the process produced a conforming part. Special processes cannot be verified that way, you cannot non-destructively confirm that a heat-treat cycle achieved the right metallurgical structure throughout the part, so the process must be controlled and the controller accredited. That distinction is exactly why NADCAP exists and exactly why milling sits outside it.
The practical implication: a shop advertising a NADCAP-accredited milling line is, at best, describing accreditation for a special process it performs in-house alongside milling, and at worst misrepresenting its credentials. When you see NADCAP attached to a machining supplier, the right question is which commodity is accredited, anodize? penetrant inspection? heat treat?, not an assumption that the milling is somehow NADCAP-blessed.
Where NADCAP actually attaches to a milled part
The accreditation matters because a milled aerospace component rarely ships as bare metal off the cutter. A typical 7075-T7351 aluminum structural fitting is milled, then deburred, then anodized or chem-filmed (NADCAP Chemical Processing), possibly penetrant-inspected for cracks (NADCAP NDT), and sometimes shot-peened for fatigue life (NADCAP Surface Enhancement). A titanium fitting may be milled, stress-relieved or solution-treated (NADCAP Heat Treating), and inspected. The milling is verifiable; every one of those surrounding special processes is not, so each must be performed by a NADCAP-accredited source.
This is where AS9100 and NADCAP interlock. AS9100 clause 8.4 makes the milling shop responsible for controlling externally provided special processes. The industry's accepted mechanism for demonstrating that control is to route those processes to NADCAP-accredited processors, because the primes recognize NADCAP accreditation as evidence the special process is under control. So a competent AS9100 milling supplier maintains an approved-supplier list populated with NADCAP-accredited anodize, heat-treat, and NDT vendors, and flows the customer's process specifications, often a prime's own spec like a Boeing BAC or a Lockheed STM, down to them.
For a buyer, the verification target is therefore split. Verify the milling shop's AS9100 (and ISO 9001 underneath it) for the machining quality system, and separately verify NADCAP accreditation on whoever performs each special process in the routing. If the milling shop self-performs anodize or NDT, its own NADCAP accreditation for that specific commodity is what you check. If it subcontracts, you confirm the named subcontractor's NADCAP status for the exact commodity and that the controlling specification was flowed down correctly.
Verifying NADCAP via eAuditNet and reading the accreditation correctly
NADCAP accreditation is verifiable through eAuditNet, the PRI-operated database that is the authoritative public record of who is accredited, for which commodities, and to what status. Unlike many quality registries, eAuditNet is specifically structured around commodity codes, so you can confirm that a supplier holds, for example, Chemical Processing accreditation rather than just a generic NADCAP claim. Always check the specific commodity, not the mere presence of a listing, because a shop accredited for Heat Treating is not thereby accredited for NDT.
NADCAP accreditation is also far more granular and harder-won than a typical ISO certificate. Audits are conducted against detailed audit criteria checklists specific to each commodity and subscope, are technically deep, and frequently surface nonconformances that must be closed before accreditation is granted or renewed. Accreditation cycles are typically annual at first and can extend with strong performance, but lapses are common because the bar is high. A red flag is an expired accreditation or one whose subscope does not cover the exact process your part needs, for instance, a plating accreditation that covers cadmium but not the hard-chrome your drawing calls out.
The scope-mismatch trap is the one that bites buyers. A processor may be NADCAP accredited for the commodity in general but not for the specific subprocess, alloy, or customer specification your part requires. eAuditNet shows the subscopes; read them. And because primes often require their own approval on top of NADCAP, confirm whether your customer's prime contractor has additional source-approval requirements that NADCAP alone does not satisfy. NADCAP is necessary and respected, but on many programs it is one layer beneath a prime's own special-process approval.
Frequently Asked Questions
A milling shop can hold NADCAP accreditation, but not for milling itself, because milling is not a NADCAP commodity. NADCAP accredits special processes whose results cannot be fully verified by inspecting the finished part, such as heat treating, chemical processing, nondestructive testing, welding, coatings, and surface enhancement. Milled features are fully verifiable by dimensional and surface measurement, so they fall outside NADCAP's scope by design. What can happen, and often does at vertically integrated shops, is that a machining supplier also self-performs a special process, say in-house anodize or penetrant inspection, and holds NADCAP accreditation for that specific commodity. In that case the accreditation is genuine but it covers the special process, not the cutting. When a supplier markets NADCAP alongside milling, ask precisely which commodity is accredited and confirm it in eAuditNet. If the answer is a vague claim that the milling is NADCAP accredited, that is either a misunderstanding or a misrepresentation, and you should treat the supplier's grasp of aerospace requirements with caution.
Most of the operations that follow milling on an aerospace part are NADCAP commodities. Chemical Processing covers anodizing, chem film or chromate conversion, passivation of stainless, and electroplating like cadmium, nickel, or hard chrome. Heat Treating covers solution treatment, aging, stress relief, and annealing, which titanium and many aluminum and steel parts require. Nondestructive Testing covers fluorescent penetrant, magnetic particle, ultrasonic, and radiographic inspection used to find cracks and inclusions. Surface Enhancement covers shot peening for fatigue life. Coatings covers thermal spray and other applied coatings, and Welding covers fusion and resistance welding where the milled part is joined. A single 7075 aluminum fitting might be milled, deburred, penetrant inspected, then anodized, touching two NADCAP commodities. A titanium part might be milled, stress relieved, and inspected, touching two more. The milling itself needs no NADCAP, but each of these downstream steps must be performed by a source accredited for that specific commodity and subscope, which is the control your AS9100 milling supplier is responsible for managing under clause 8.4.
Use eAuditNet, the Performance Review Institute database that is the authoritative public record of NADCAP accreditations. Search the supplier and confirm not just that a listing exists but that it holds the specific commodity your part needs, Chemical Processing, Heat Treating, NDT, and so on, because accreditation in one commodity does not extend to others. Then read the subscope, which is where buyers get caught: a processor may be accredited for Chemical Processing generally but not for the specific finish, alloy, or customer specification your drawing calls out, such as hard chrome versus cadmium, or a particular Boeing or Lockheed process spec. Confirm the accreditation is current, since NADCAP cycles are demanding and lapses are common, and an expired accreditation means the process is no longer under recognized control. If the milling shop subcontracts the special process, verify the named subcontractor in eAuditNet and confirm the controlling specification was flowed down. Finally, check whether your prime contractor requires its own source approval on top of NADCAP, because on many programs NADCAP is necessary but not sufficient.
No, they are complementary and cover different things. AS9100 is the aerospace quality management system standard that governs how the milling shop runs, its document control, calibration, inspection, nonconformance handling, first-article inspection, and crucially its control of externally provided processes under clause 8.4. NADCAP is special-process accreditation that demonstrates a specific process like anodize or heat treat is technically under control. A milling supplier needs AS9100 for the machining quality system; it does not need NADCAP for the milling because milling is not a NADCAP commodity. Where the two connect is that AS9100 makes the milling shop responsible for ensuring outsourced special processes are controlled, and the industry-accepted way to show that control is to route those processes to NADCAP-accredited sources. So a strong aerospace milling supplier holds AS9100 itself and works exclusively with NADCAP-accredited processors for the special processes its parts require. Verifying one does not verify the other: check AS9100 in OASIS for the machining quality system, and check NADCAP in eAuditNet for each special process in the routing.
The NADCAP-accredited processing steps are usually a larger driver of cost and lead time than the milling itself on aerospace parts. NADCAP processors charge a premium because the accreditation is expensive to obtain and maintain, audits are deep and frequent, and the process controls and documentation are extensive. Each routed step, anodize, heat treat, penetrant inspection, shot peen, adds its own lot charge, queue time, and transit time between the machine shop and the processor, and these steps are typically serial rather than parallel, so they stack. A part needing milling plus two NADCAP processes can spend more calendar time in finishing and inspection queues than on the spindle. The cost premium and schedule stretch are inherent to the assurance NADCAP provides and are not something a buyer should try to engineer away on flight hardware. The optimization levers are consolidating processes where the drawing allows, choosing milling suppliers with strong NADCAP-accredited subcontractor relationships and short queues, and locking the routing early so re-sourcing a lapsed or scope-mismatched processor does not blow the schedule late in the program.
Last updated: July 2026
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