Mark Hammar When implementing your aerospace Quality Management System (QMS) you will very likely come across the concept of key characteristics in your customer requirements, even before you review the requirements of AS9100 Rev D. This concept, and the necessity to manage the key characteristics of a product, are deeply ingrained in the fabric of aerospace quality management; however, not everyone understands the terms and requirements well.
Here is a bit about what key characteristics are and what you need to do about them.
What are key characteristics?
The term “key characteristics” shows up a lot in the terms and definitions of AS9100 Rev D, with most of these special terms relating in some way to key characteristics; so, what is a key characteristic? A key characteristic is a feature or attribute that, when it varies from the ideal, has a significant effect on the ability of your product to meet requirements, and also requires specific action to control variation. These key characteristics can then become critical items, leading to special requirements as per the definitions in AS9100 Rev D. So, how exactly do we determine key characteristics, then?
There are two criteria, as defined above, which must be met for a key characteristic:
- Does the attribute or feature significantly affect the product usability? – This usability includes form, fit, function, performance, service life, or producibility. So, are there any features that can affect this significantly – a particular dimension that absolutely must be within the exact tolerance or it will not fit, an electronic parameter that must be within a certain range, or an important attribute of your process that must stay within a certain boundary?
- Do you require specific actions to control the variation? – If there is no way that the feature or attribute can vary from the nominal design and become non-conforming, then it is not a key characteristic that needs to be addressed. For instance, if a machine needs to maintain a certain pressure, which needs to be checked and adjusted routinely, this would be a key characteristic of the process.
If you answer yes to both of these questions, then you have a key characteristic to deal with. Below are the steps you need to take.
To find out more about the special aerospace definitions in AS9100 Rev D, see this article: Five special aerospace terms in AS9100 Rev D.
What steps need to be taken?
There are a few basic steps to take when dealing with variation management of key characteristics as defined throughout AS9100 Rev D:
- Identify the key characteristics – These characteristics may be identified by the customer, or may come from the design process (clause 8.3.5). Remember, they need to meet both criteria above, so don’t go overboard identifying everything as a key characteristic.
- Identify the actions needed to control the variation of the key characteristics – Plan what actions will need to take place in your processes to ensure the key characteristics will remain within their designated variation (clause 8.1f). This may involve identifying critical items or special requirements that need to be controlled.
- Identify the controls to put in place to ensure the actions – Plan the controls to be put in place within your processes (clause 8.1f), such as additional inspection of a key characteristic or additional maintenance of tooling to avoid wear.
- Include this information for external providers, if necessary – If a key characteristic will be under the control of an external provider (clause 8.4.3h), the information on the key characteristic, including the controls that need to be in place, must be included in the information to the provider.
- Put production and service controls in place – What controls from step 3 and monitoring do you need in place to track the variation and acceptability of the key characteristics in your processes? Implement these within your processes, such as in your process documentation or training, so that these controls are carried out.
Once these controls are in place, you then need to use them as part of your QMS processes, correcting any nonconformities and taking corrective action where necessary as you would with any other controls. These five steps ensure that you identify what controls need to be in place within your QMS processes, and then update your processes accordingly.
If you have key characteristics that have been identified by your customer, or during your design process, you may want to investigate a more detailed key characteristics management process. AS9103, Variation Management of Key Characteristics, is a supporting standard that gives a best practice for managing this activity. For more on the standards that support AS9100 Rev D, see this article:How Do AS9101, AS9102, & AS9103 Relate to AS9100 Rev D?
Variation of key characteristics: Critical to your business
While your products and services may not include any key characteristics, many within the aerospace industry do. When this is the case, it is critical that these characteristics are identified, controlled, and monitored so that their variation does not affect the safety or performance of the product or service affected. So, if you do have a product or service with a key characteristic, think of this as one risk management activity that can benefit your ability to successfully provide the products and services that your customers need.
Read this free white paper: Clause-by-clause explanation of AS9100 Rev D to understand product requirements.
