Every aerospace shipment worth accepting arrives with a certificate of conformance, and almost every quality escape investigation ends up reading one. For such a routine document, the CofC is widely misunderstood. Buyers over-trust it, treating it as proof of test results it never contained, or under-trust it, dismissing it as paperwork theater. Both mistakes are avoidable. A certificate of conformance does one specific job, does it well, and does nothing else. This article covers what the document attests, what it does not, and how to put it to work at receiving.
Key takeaways
- ✓A certificate of conformance is a signed attestation that the product supplied conforms to the purchase order and the specifications it references.
- ✓It carries identity and traceability: part number, quantity, lot or batch, and the chain of custody back toward the manufacturer.
- ✓It is not a material test report and not dimensional inspection data: it certifies conformance, it does not demonstrate it.
- ✓AS9120 distributors do not alter product, so their job is to pass manufacturer certificates through with lot linkage intact.
- ✓Documentation requirements belong on the purchase order: the time to ask for material certs or test reports is before the buy, not after delivery.
What a CofC Actually Attests
A certificate of conformance is a declaration by the supplier, signed by an authorized representative, that the goods supplied conform to the requirements of your purchase order and the specifications, standards, and drawings it invokes. Read that carefully: the anchor is your purchase order. The certificate typically states the part number and, where applicable, the revision, the quantity, the lot or batch identity, the governing specification, and the identity of the party making the attestation.
Its second job is traceability. In a distribution chain, the CofC is one link in a chain of custody that should run from the manufacturer, through each distributor that handled the product, to your dock. Each party certifies what it did and points backward to the party before it. When the chain is intact, you can answer the question every auditor eventually asks: how do you know this part is what its label says it is?
What a CofC Is Not
A CofC is a statement of conformance, not a package of evidence. Specifically:
- It is not a material test report. A CofC contains no chemistry, no mechanical test results, no heat treat data. If your drawing requires proof of material properties, that proof lives in a mill or material certificate, which is a separate document.
- It is not dimensional inspection data. The certificate does not tell you that anyone measured the parts in your box, and it is no substitute for your own receiving inspection.
- It is not automatic airworthiness. Conformance to the purchase order is only as good as the purchase order. A certificate cannot repair requirements that were never flowed down in the first place.
None of this makes the CofC weak. It makes it specific. The signature converts a shipment from anonymous hardware into a formal, attributable claim, and attributable claims are what quality systems, audits, and recourse are built on.
How AS9120 Distributors Pass Certificates Through
A stocking distributor certified to AS9120 does not manufacture, alter, or repair product, and that shapes what its certificates mean. The distributor's CofC attests to what a distributor controls: that the product supplied is the product received from the source shown, in the quantity and lot stated, stored and handled properly, with the manufacturer's documentation preserved and passed through. When a lot is split across customers, AS9120 controls require the split inventory to stay linked to the original certificates.
That is the real content of the certification: an audited system for not breaking chains. For the fuller picture of what the standard covers, and how it differs from a manufacturer's AS9100, see our guide to AS9120 vs AS9100.
What Buyers Should Check at Receiving
- Identity match. Part number, revision where applicable, and quantity on the certificate should match the purchase order, the packing slip, and the markings or labeling on the product itself.
- Lot linkage. The lot or batch on the certificate should match the labeling, and the chain should reach back toward a named manufacturer rather than dead-ending at a distributor.
- Specification and revision. If your purchase order invoked a specific revision, the paperwork should support it.
- Document integrity. Inconsistent fonts, altered dates, vague source names, and certificates photocopied through too many generations are the classic red flags. Our article on AS6081 counterfeit prevention covers what those flags mean and what to do about them.
When to Ask for More Than a CofC
Some buys need more than an attestation. Ask for material certificates when the drawing requires raw material traceability. Ask for test reports when properties such as strength or hardness must be demonstrated rather than certified. Ask for first article or dimensional data when the contract or the application demands it. The critical habit is timing: these requirements belong on the purchase order, agreed before the buy. Requesting a mill certificate after delivery, for product that was quoted without one, is a much harder conversation.
At Instaparts, every shipment includes a certificate of conformance with full AS9120 traceability, and documentation requirements can be raised at quote time. Browse the parts catalog and put the paperwork question to us before the PO, where it belongs.