key characteristics

Key characteristics commonly refer to specific product or process features that have a significant impact on fit, form, function, safety, performance, or regulatory compliance, and therefore require defined control and verification. They are usually identified during design and process planning and then tracked through manufacturing, inspection, and change control.

What key characteristics include

In regulated and industrial manufacturing environments, key characteristics typically include:

• Dimensions or tolerances that are critical to assembly or performance (for example, hole location for a structural fastener pattern)
• Material properties that affect strength, durability, or safety (for example, heat treat hardness, coating thickness)
• Functional parameters that influence system operation (for example, flow rate, torque, electrical resistance)
• Process parameters that must be controlled to consistently achieve product requirements (for example, weld current, curing time, oven temperature)

Key characteristics are usually called out in design documentation, control plans, or quality plans and are linked to specific inspection or monitoring activities.

Key characteristics in aerospace and AS9102 / FAI

In aerospace and other highly regulated sectors, key characteristics are often tied to formal first article inspection (FAI) and ongoing production controls:

• Design authorities may flag certain characteristics as critical or key on drawings or models.
• During FAI (for example under AS9102), these characteristics must be clearly ballooned, referenced on characteristic reports, and verified with objective evidence.
• Manufacturing and quality systems may require specific inspection frequencies, measurement methods, gage controls, or capability studies (for example, Cpk) for these characteristics.
• Changes affecting key characteristics often trigger additional review, risk assessment, or repeated FAI.

How key characteristics are used operationally

Operationally, identifying key characteristics helps organizations focus limited inspection and process-control resources on the most important features:

• Design and planning: Engineering and quality teams determine which features are key, document them, and define how they will be controlled and measured.
• Work instructions and routings: Digital or paper travelers, work instructions, and control plans highlight key characteristics, including required tools, methods, and acceptance criteria.
• Inspection and data collection: MES, SPC, or inspection systems capture results for key characteristics, often with tighter rules for data integrity, sampling plans, and reaction plans.
• Change management: Any design, process, or supplier changes that might affect key characteristics typically go through formal review and approval, and may require revalidation.

Common confusion

• Key characteristics vs. critical characteristics: Some organizations treat these as equivalent terms; others use a hierarchy where “critical” is reserved for safety-of-flight or life-critical features, and “key” is a broader set of high-impact features. Usage is organization- and standard-specific.
• Key characteristics vs. all drawing characteristics: Not every dimension or note on a drawing is a key characteristic. Key characteristics are the subset that have been explicitly designated as requiring special control.
• Product vs. process characteristics: Product key characteristics describe the physical or functional outcome, while process key characteristics describe the process variables that must be held within limits to consistently achieve that outcome.

Relation to the provided context

In an AS9102-compliant workflow, key characteristics are typically:

• Identified from approved design data and highlighted during drawing or model ballooning.
• Explicitly listed and inspected in FAI documentation, with traceable measurement results.
• Subject to defined controls in the quality management system, including how nonconformances and changes are handled.