Back in 2001, a new word appeared in the aerospace heat-treatment lexicon in Europe: Nadcap. For suppliers, this was a venture into the unknown. Nadcap meant an audit, but it was often considered as “just another quality audit.” By 2004, however, the very mention of Nadcap seemed to fill people with fear and foreboding. My impression today is that this attitude has changed. A Nadcap accreditation is now seen as the “gold standard” in aerospace heat treatment.


Nadcap audits are hard because they are detailed and performed by technical experts. But there are no unrealistic expectations. Nadcap audits check that work is done in conformance with customer requirements, which is exactly what should be happening anyway.

In my view, Nadcap audits in Europe have led to a gradual improvement in documentation, equipment and best practices for heat treatment.

Two Audits 15 Years Apart: Much has Changed

In my early days of auditing, Nadcap had only just arrived in Europe, and most companies were experiencing this new special-process audit for the first time. It was normal to write more than 25 nonconformances during a four-day audit.

The worst company I ever visited received 49 nonconformances over five days. Everything I looked at had errors, mistakes, missing information or was just plain wrong. They had ISO 9001 but had never had anyone take a really close look at their heat-treatment process. Many charts were illegible. Records often stopped before parts were taken out of the furnaces, hence no times could be confirmed. Heat-treatment times and temperatures were seen as “recommendations” – even when they were on instruction sheets signed by the customer.

At that time, their furnace testing was to BS 2M54, but it was sporadic and inconsistent. As long as a furnace passed a test, it was considered acceptable even if the test was late. All decisions were made by the only person on site who knew anything about heat treatment (the metallurgist).

This was a company that would willingly accept aerospace work with the instruction “please heat treat” with no further details, such as confirmation of quantities, the material or whether the parts were to be made hard or soft. Such details were confirmed by telephone, but there were no records of any calls or discussions. Operators would do as they saw fit. No one challenged them because the supervisors were equally ignorant of requirements. Training was on-the-job, delivered by workmates and evaluated by the supervisors. It was a hard audit to conduct, demonstrated by the fact that the closing meeting took four hours.

Today, the average number of nonconformances in a Nadcap audit is less than seven. A few weeks ago, I did another audit on a similar-sized operation. There were no (zero) nonconformances. Every chart was clear and legible. All work had clear and explicit instructions. At Goods Inwards, all incoming work was triaged against customer requirements (aerospace, medical, oil and gas, commercial) where different levels of control were applied and different equipment could be used. Everyone understood what they were doing and, crucially, why they were doing it. The equipment was managed in accordance with customer requirements. In most cases, this meant applying AMS 2750 for pyrometry. It was a joy to audit this company, and in stark contrast to my experiences of old, the closing meeting took only 10 minutes.

What has changed over the last 15 years?

Nadcap audits are in essence very simple. Auditors check what the customer asked for, what the operators were told to do and what was actually done. If anything goes wrong, we need to see how that was handled. Nadcap enforces knowledge and understanding of the rules by simply identifying where the practices differed from the requirements.

To a casual visitor, the biggest and most visual change is the almost complete conversion to electronic recording. The introduction of digital chart recorders, where data is logged in real-time and can be transferred to remote servers, has been a revolution. Operators and the Quality team can check every process without the need for the large layout tables on which we used to unroll the (often illegible) charts. Real-time logging has made furnace oversight easier. This use of electronics extends to control systems.

Controllers have become more sophisticated but are still limited by the heating systems to which they are attached. Programmable systems have become better as manufacturers have responded to the need for the programs (which you could liken to heat-treatment recipes) to be managed as if they were secure instructions.

The way in which companies create instructions and procedures has also improved. They now understand that simply cutting and pasting sections from their customer specifications does not generate a robust work instruction.

Nadcap has been clear that all activities require instructions (procedures, SOPs) that state how things are actually done, not simply what is to be done. In Europe we had a good basis for this in the process-data-card or instruction-sheet approach. These systems have developed and are now often computerized. The real changes have been in the breadth and detail of instructions for related activities such as hardness testing, conductivity testing and, of course, pyrometry.

In 2004, every major customer had their own standard for the management of thermal-processing equipment. Some were so different from others that they were essentially incompatible. The rollout of Nadcap introduced Europe to the U.S. pyrometry standard AMS 2750. Since then it has been adopted as the baseline requirement by almost every aerospace customer and is now also being used by the automotive, nuclear, medical and offshore markets.

Awareness of AMS 2750 has risen as has the level of understanding of the users. The standard itself is complex rather than difficult and is relatively easy to understand once you take the time to properly study it.

Because of the standard’s importance and complexity, the Performance Review Institute (the organization that administers Nadcap) developed a training course on it through their professional-development program, eQuaLearn, more than 10 years ago. To date in Europe, more than 1,700 people have received training in the content and intent of AMS 2750.

The results of this training show in audits. While errors in pyrometry are still the single most-common group of issues found, the nature of them has changed. Ten years ago, one issue was that furnaces did not meet the uniformity requirements, but the tests were misapplied or the results were misinterpreted. Today, auditors are more likely to find mistakes in calculations or in the details of the methods. I honestly think that the awareness of the rules and requirements has never been better.

Better awareness of the rules also reflects in better equipment. If equipment is failing a pyrometry test, then it needs to be fixed. Nadcap has been rigid in applying the requirements, from AMS 2750 and from customers, for preventive maintenance. I no longer see holes in brickwork, furnace doors that do not close, quench tanks with faulty (noisy) pumps, or vacuum furnaces with flaking inner walls or blocked cooling channels.

The last major difference between the industry of 15 years ago and now is its approach to training. For heat treatment, it has resulted in more formal training systems with meaningful periodic evaluations. In the early days of Nadcap, I would find operators who only knew how to move parts from A to B. Now operators generally understand how the furnace works, know what to look for as “not normal” and have some understanding of basic metallurgy. Almost all companies that I visit recognize that there is a severe shortage of metallurgists and engineers who understand heat treatment. Many of them are now arranging internal training and development to ensure that decisions are made by persons who are documented as competent and knowledgeable.

Almost lost in these changes are the creeping improvements that come from a gradual rationalization or (in some cases) tightening of specifications. Better control of the processes, which is at the heart of the Nadcap program, has allowed both the removal of some requirements and the tightening of others. The end result, in my opinion, is that heat-treatment operations for aerospace in Europe are better managed, better controlled and are delivering fewer defective parts.


For more information: Contact Adrien Boespflug, marketing and communications coordinator. E-mail:; tel: +44 (0) 870 350 5022