Most quality audits allow a conversation. An auditor raises a clause, you explain your approach, and if your reasoning is defensible, you pass. Nadcap is not that audit. When the auditor opens AC7108 for welding, AC7109 for NDT, or the chemical processing checklist, the question is binary: does the objective evidence match the criterion as written, or does it not?
Your interpretation of the requirement carries no weight, because the auditor is not interpreting either. The checklist is a contract between the supplier, the prime contractors, and the governing engineering bodies. That is why experienced suppliers treat Nadcap differently from any other audit they host: there is no auditor discretion to lean on.
I learned this early in my aerospace career. A heat treat facility I supported had well-trained staff and one minor deviation in thermocouple calibration interval handling. Under a customer audit we would have closed it with a corrective action commitment. Under AC7102 it was a nonconformance requiring closure before accreditation, which meant a supplemental audit. The finding was small. The consequence was not.
How the Checklists Are Built and Why They Read That Way
Nadcap checklists are not written by a certification body generalising across industries. They are maintained by working groups of prime contractor materials engineers, process engineers, and suppliers — the people who have seen the failure modes firsthand. The heat treat checklist asks about furnace temperature uniformity surveys because uneven furnaces produce parts that pass surface hardness checks while hiding untransformed microstructure beneath.
The NDT checklists ask about personnel certification because an uncertified inspector reading a penetrant indication is not a quality control step at all — it is a false sense of security. Every criterion traces to a real, known failure in aerospace hardware. Understanding which failure a criterion guards against is what separates suppliers who comply from suppliers who conform.
Each checklist has a general section covering quality system expectations for the commodity, then technical sections mirroring the process flow. Chemical processing covers bath composition control, analysis frequency, solution records, rack loading, and current density for anodising. Welding covers welder qualification, filler metal control and storage, joint preparation, and destructive and non-destructive acceptance evidence. Materials testing covers calibration traceability and specimen handling.
Every criterion references an underlying specification — AMS, ASTM, or prime customer specifications — and the auditor verifies against the current revision. If your procedure cites a superseded revision, that is a finding regardless of whether your process is technically sound. Currency of reference documents is among the most common and most avoidable nonconformances I have seen in this scheme.
Self-Audit Discipline: Rehearsing Against the Real Checklist
Suppliers who pass Nadcap comfortably audit themselves with the actual checklist, at the actual frequency, against actual records — as routine, not as a pre-audit scramble. Obtain the current revision, sit down with the process owner and the evidence, and go criterion by criterion. For every comply response you must be able to point to a document, a record, or a demonstration the auditor could verify on the day.
The distinction is strict. We have always done it that way is not evidence. The furnace chart from last Tuesday showing the soak is evidence. A disciplined self-audit uncovers what daily routine hides: a plating lab whose own calibration lapsed while the bath analysis log stayed current, a blacklight intensity check performed at the wrong distance, filler wire in inventory that the weld procedure no longer permits.
None of those examples are exotic. All of them are checklist findings waiting for an auditor with a torch and a file request. Two rules keep the self-audit honest. First, the person doing it must not own the process — fresh eyes read the criterion literally, the way the auditor will. Second, self-audit findings must go through the same corrective action rigour as real findings: root cause, correction, verification of effectiveness.
If you self-audit and quietly fix things without records, you have trained your organisation to hide rather than to learn — and the auditor will eventually find what your self-audit buried. The self-audit is not insurance paperwork. It is the last technical review between your process and the hardware, and it deserves the same seriousness as the audit it rehearses.
What the Auditor Actually Does on the Day
Expect the Nadcap audit to be evidence-heavy and floor-focused. For NDT, the auditor will request current ASNT or NAS-410 certification for every method and every level of responsibility, with vision tests within interval and documented training hours. In heat treat, expect the auditor to trace a specific production lot from work order through furnace load chart, temperature recorder output, and the pyrometry records proving temperature uniformity survey and system accuracy test currency.
In chemical processing, the auditor walks the line: tanks labelled and analysed per the frequency in the process specification, solution make-up records with correct chemical additions, rejected or contaminated baths identified and segregated. Racking configurations matter, because loading parts too densely in an anodising bath changes current distribution — the checklist and the underlying specification both address it.
In welding, expect live examination of welder continuity records, storage oven temperatures for low-hydrogen electrodes, and the traceability of a production weld back to the qualified procedure and the welder who ran it. One behaviour I insist on from my teams: never argue the criterion during the audit. If you believe a criterion does not apply to your scope, raise it with the staff engineer through the formal query process before or after — never as a debate at the workstation. Spend the audit hours producing evidence, not advocacy.
Lot traceability the auditor will demand in heat treat
- 01Work orderThe auditor selects an actual production lot, not a showcase one.
- 02Furnace load chartLoad composition and placement matched against the procedure.
- 03Recorder outputSoak time and temperature evidenced by the chart, not by memory.
- 04Pyrometry recordsTemperature uniformity survey and system accuracy test both in currency.
The Cost of a Finding
A Nadcap finding is expensive well beyond the corrective action. Nonconformances must be closed through eAuditNet with root cause and corrective action evidence, and depending on severity and quantity, closure may require a supplemental audit — a separate visit with its own fee schedule and its own scheduling queue. During the gap between a failed audit and reaccreditation, your listing shows the gap, and prime buyers watch that listing. A lapse can stop awards mid-programme.
Then there is customer fallout. When an accredited special process supplier receives a finding, customers who flowed down their process requirements often demand containment on parts processed through the affected process: retrospective review, possible re-inspection or destructive sampling, occasionally scrap. A single furnace calibration gap can cascade into reviewing months of thermal processing records across dozens of part numbers. The direct audit fee is the smallest line on that invoice.
The finding itself is small only until you count the containment, the supplemental audit, and the months of records it forces open.
Nadcap audits recur on a cycle set by your performance history and the commodity. Strong performance earns longer intervals and, in some commodities, reduced-scope audits. Repeated findings bring shorter intervals and deeper scrutiny. Your audit outcome sets the terms of your relationship with the scheme for years. I have watched good facilities earn their way from annual full audits to a lighter touch, and I have watched others spiral into supplemental audits that consumed quality resources for the better part of a year.
Why Nadcap Sits Outside the Management-System World
Nadcap sits deliberately apart from the management-system audit world. Your ISO 9001 registration, your customer audits, even IATF 16949 assessments allow a degree of tailoring and professional judgement about whether your system achieves its intent. Nadcap audits a special process, not a system. The question is not whether your quality management is sound; it is whether this tank, this furnace, this inspector, this procedure, and this record conform to criteria written by engineers who know exactly how hydrogen embrittlement is missed and how a cadmium-plated fastener fails in service when post-plate baking was shortened.
That narrowness is the point. Special processes — heat treat, plating, NDT, welding, materials testing — share a common hazard: you cannot inspect the result into the part. The properties are created by the process or they are not there at all. Penetrant inspection cannot find a defect an unqualified inspector overlooked, and a weld's fusion cannot be verified on every production part.
Management-system audit versus Nadcap audit
System audit (ISO 9001, IATF 16949)
- Judges whether the system achieves its intent
- Reasoned explanation can close a finding
- Auditor exercises professional discretion
- Scope is the whole management system
Nadcap special process audit
- Judges conformity to criteria as written
- Evidence must match the criterion word for word
- Auditor records objective evidence, no interpretation
- Scope is one tank, furnace, inspector, procedure, record
That is why the primes demand the process itself be accredited, repeatedly and without interpretive mercy: it is the only control that genuinely protects the flying hardware. A sound QMS makes a special process more likely to be run well, but it cannot substitute for demonstrating that the specific process, on its specific records, meets engineering criteria written against known failure modes.
Working the Checklist as Engineering Documentation
Treat the checklist as engineering documentation, not compliance paperwork. Read the underlying specifications it references. Understand why each criterion exists and which failure mode it guards against. When that understanding is in place, the self-audit stops feeling like a chore and becomes what it actually is: the last technical review between your process and the parts that keep aeroplanes in the air.
Across two decades in automotive and aerospace quality, I have seen the pattern hold consistently. Suppliers who embrace the checklist as engineering build better processes, not just better audit outcomes, and their performance history earns them the longer audit intervals and lighter scopes the scheme rewards. Suppliers who treat it as paperwork to survive periodically stay on the short cycle.
The practical sequence never changes: verify reference document currency first, because it is the cheapest finding to prevent. Then walk the floor with the checklist in hand, in the shoes of someone who did not write the procedures. Then close what you find with real corrective action, recorded. Do that routinely, and the audit itself becomes confirmation rather than exposure.