AS9103 Key Characteristics: The Complete 2026 Guide

AS9103 key characteristics requirements tell aerospace producers how to manage variation on the features that matter most: the dimensions, material properties and process parameters where variation significantly affects fit, performance, service life or manufacturability. If a customer drawing flags a key characteristic, AS9103 is the standard that explains what you are expected to do about it, and it goes much further than simply inspecting the feature.

This guide to AS9103 key characteristics explains what AS9103 is, what changed in revision B, how it relates to AS9100 and AS9145, and how to build a key characteristic control process that satisfies customers and auditors.

What Is AS9103?

AS9103 is the IAQG standard titled “Variation Management of Key Characteristics,” published in the Americas by SAE. The current revision is AS9103B, revised in August 2022, following the original 2001 issue and revision A in 2012.

The standard is aimed mainly at new parts and products entering production, but it can be applied to parts already in production. It covers production processes that influence variation of key characteristics, and also maintenance and service processes where key characteristics are identified. It applies at every product level from basic material such as castings and forgings up to assemblies, and producers must flow its requirements to their own external providers.

AS9103 is not a certification standard. It becomes mandatory when a customer invokes it through a contract, purchase order or supplier quality requirements.

What Counts as a Key Characteristic

AS9100D defines a key characteristic as an attribute or feature whose variation has a significant effect on product fit, form, function, performance, service life or producibility, and that requires specific actions to control variation. AS9103B adds clarity with related terms:

• Product key characteristic: a feature of the product itself, typically identified by the design authority on the drawing, model or specification.
• Process key characteristic: a process parameter that can be measured and controlled to manage variation of a product characteristic, such as spindle speed, temperature or cure time. These are typically identified by the producer.
• Substitute key characteristic: a characteristic measured in place of one that is difficult or impossible to measure directly.

Key characteristics are not the same as critical items or safety-critical characteristics. A characteristic can be key because variation drives scrap and assembly problems, even with no safety implication.

What Changed in AS9103B

The IAQG’s published summary of the revision describes several shifts in emphasis:

• Alignment with AS9100:2016 and AS9145, including adopting AS9145’s terms “product KC” and “process KC”
• A focus on process KCs, since identifying product KCs is the design authority’s job through design risk analysis
• Control plan requirements in an appendix adapted from AS9145, so AS9103 can be used with or without a full APQP program
• Measurement systems analysis (MSA), statistical process control (SPC) and process capability as core elements, with control charts and capability studies both required rather than one replacing the other
• Variation reduction and ongoing process monitoring as the purpose, with containment of nonconforming product left to AS9100

How AS9103 Key Characteristics Relate to AS9100 and AS9145

Standard	Role	Key characteristic link
AS9100D	Quality management system	Defines key characteristic; requires critical items and KCs to be identified and controlled, and flowed down to providers (8.4.3)
AS9145	Advanced product quality planning (APQP) and production part approval process (PPAP)	Builds KC identification and control plans into new product introduction
AS9103B	Variation management of key characteristics	Detailed method for controlling KC variation in production: control plan, MSA, SPC, capability
AS9102	First article inspection	Verifies that KCs, along with all characteristics, conform on the first production article

In short: AS9100 says control them, AS9145 plans them into the product, AS9103 tells you how to manage their variation, and AS9102 checks them on the first article. Our first article inspection guide explains the AS9102 forms.

The AS9103 Key Characteristics Process, Step by Step

1. Identify the key characteristics. Start with those flagged by the customer or design authority. Then identify process KCs: the process parameters that drive variation in the product KCs.
2. Plan the process. Map the manufacturing flow and determine where each KC is created and where it can be influenced.
3. Create a control plan. For each KC, define the specification, the measurement method, sample size and frequency, the control method (for example an X-bar R chart) and the reaction plan.
4. Validate the measurement system. Run MSA, such as gauge repeatability and reproducibility, to confirm the measurement variation is small relative to tolerance. Data from a poor gauge cannot support SPC.
5. Establish statistical control and capability. Collect data, confirm the process is stable, then calculate capability indices against customer targets.
6. Monitor and react. Run SPC in production with clear out-of-control rules and documented reaction plans.
7. Reduce variation. Where capability is insufficient, use problem-solving and process improvement to reduce variation, and keep 100% inspection or other containment until capability is demonstrated.
8. Flow down. Where an external provider creates or affects a KC, flow down the requirement and verify their control.

Common Problems With AS9103 Key Characteristics Control

• Inspecting instead of controlling. Measuring every part and sorting bad ones is containment, not variation management.
• SPC without MSA. Control charts built on an unvalidated gauge mislead everyone.
• Charts nobody reacts to. Out-of-control signals with no documented reaction undermine the whole system.
• Control plans that do not match the router. The shop floor should run the plan that the quality team wrote.
• No flow-down. A KC created at a special process supplier is still your responsibility.
• Uncontrolled changes. Changing a process KC parameter without review can shift capability; link this to configuration and change control.

What Auditors and Customers Look For

• A procedure for identifying and controlling key characteristics
• Control plans for each part number with KCs
• MSA records for the gauges used on KCs
• Control charts and capability studies, with evidence of reaction to signals
• Flow-down of KC requirements on purchase orders
• KC verification in first article inspection reports

Building the Supporting Quality System

AS9103 sits on top of a working AS9100 system. As of October 2026, AS9100D remains the certifiable revision, and the IAQG’s planned successor, IA9100, has not been published. The AS 9100 Toolkit provides 38 editable templates aligned to AS9100D, including production control, first article inspection and configuration management documents that support key characteristic control. For the full picture of the AS9100 family, see our guide to aerospace quality management, and for related change control, read our AS9100 configuration management guide.

Getting Started With AS9103 Key Characteristics

If a customer has just invoked AS9103 key characteristics requirements for the first time, a phased start keeps the work manageable:

1. Inventory: list every part number with customer-identified KCs and confirm the current drawing revision.
2. Prioritize: start with high-volume parts and those with recent nonconformities on KC features.
3. Gauges first: complete MSA on the gauges used for those KCs before collecting SPC data.
4. Pilot one part: build the control plan, collect data, calculate capability and agree reaction rules.
5. Roll out: apply the template to remaining parts and flow requirements to suppliers.
6. Review: report KC capability at management review and track improvement actions.

Training matters as much as forms. Operators need to understand what a control chart signal means and what to do, and engineers need practical MSA and capability skills. Record that training as competence evidence. Done well, AS9103 key characteristics control reduces scrap and rework, which usually pays back the effort.

Writing a Control Plan for AS9103 Key Characteristics

The control plan is the working document that ties everything together. For each key characteristic, a usable control plan records:

• Part number, revision and operation number where the characteristic is produced
• Characteristic description, specification and tolerance
• Whether it is a product KC or process KC, and any linked substitute characteristic
• Measurement method, gauge identification and MSA status
• Sample size and frequency
• Control method, such as the type of control chart
• Reaction plan when a point falls outside control limits or a trend appears
• Responsible role for measurement and for reaction

Keep control plans under document control and link them to the router or traveler, so a change to the process triggers a review of the plan. That link is often what auditors check first.

Frequently Asked Questions

Is AS9103 mandatory for AS9100 certification?

No. AS9100 requires key characteristics to be identified and controlled when they exist. AS9103 becomes mandatory when a customer invokes it in a contract or supplier requirements.

Who identifies key characteristics?

The design authority, usually the customer, identifies product key characteristics on the design data. The producer typically identifies process key characteristics that influence them.

What capability index do customers require?

AS9103B does not set one universal value. Customers define capability targets in their own requirements, and you should confirm them before production.

Are AS9103 key characteristics checked during AS9100 audits?

Where customers invoke AS9103 or flag key characteristics, AS9100 auditors may sample control plans, SPC records and flow-down to verify that the requirements are being met.

Do process key characteristics need customer approval?

Requirements vary by customer. Some expect process KCs and control plans to be submitted for review, especially when AS9145 PPAP applies; others only expect them to be available on request. Check your customers’ supplier requirements.