# Key Characteristics (AS9103)

> Source: https://netray.co/glossary/key-characteristics
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Glossary

## Short answer

Key characteristics are the features of a material, part or process whose variation has a significant influence on product fit, form, function, performance, service life or manufacturability, and which therefore get special control under AS9103 variation management.

## Aliases

- KC
- key characteristic
- AS9103
- variation management
- critical characteristics

## Category

manufacturing

## Full Definition

Not every dimension on a drawing deserves the same attention. Designers identify key characteristics (KCs) where variation matters most, such as a bore diameter that controls a bearing fit or a seal surface finish. Critical items related to safety are managed separately under stricter rules, and customers define how each is flagged on drawings.

AS9103 is the aerospace standard for variation management of key characteristics. It describes how to identify KCs, determine the process capability needed, plan controls, monitor with statistical methods, and react when the process shifts. Suppliers typically demonstrate capability with metrics such as Cp and Cpk, and customers set acceptance targets in the contract or the quality requirements flowed down.

KCs link several tools. The design FMEA and process FMEA help decide what is key, the control plan defines how each is measured, SPC charts show whether the process remains stable, and the first article inspection report under AS9102 identifies each KC as characteristic accountability. The more consistently these are tied together, the easier audits become.

In ERP and QMS terms, KCs show up as inspection plan characteristics with a KC flag, frequency rules, gauges and specification limits. Results are collected at in-process or final inspection, and failures create a nonconformance linked to lot and serial. ERP quality modules in SyteLine, Infor LN, SAP QM and others can hold the plan, while charting often lives in SPC software.

## Why It Matters

- Customers contractually require evidence of capability on KCs, and failure to show it can restrict approval of the part.
- Focused control on key features is cheaper than inspecting every feature at the same level.
- A shifting process is detected early by SPC, before it produces nonconforming parts.
- KC data supports root cause investigation and supplier corrective action.

## In Practice

Example: a drawing marks bore diameter 25.000 +0.013 mm as a KC with a required Cpk of at least 1.33. The inspection plan samples five pieces per lot and records readings. Over ten lots the Cpk comes out near 1.1, which is below target, so the team investigates tool wear and adds a compensation step. The gotcha is calculating Cpk from too few samples or from data that mixes machines, which hides the real behaviour.

## Faq

### What is AS9103?

**Answer:** AS9103 is the aerospace standard for variation management of key characteristics. It sets out how to identify them, assess process capability, control and monitor them.

### What Cpk is required for key characteristics?

**Answer:** It is set by the customer or contract rather than by the standard. A value of 1.33 is commonly seen, but always use the requirement in your purchase order or quality flow-down.

### Is a key characteristic the same as a critical item?

**Answer:** No. Critical items are tied to safety or flight-critical risk and carry stricter controls. Key characteristics cover features with significant influence on fit, function or performance.

## Search terms

key characteristics aerospace, AS9103 variation management, key characteristic Cpk, KC vs critical characteristic, key characteristics drawing, variation management key characteristics, KC control plan, AS9103 requirements

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