Under AS9100, rework, repair, and use-as-is are three different ways to disposition nonconforming product. They are not interchangeable, and each has different implications for design authority, risk, documentation, and customer approval.
Rework
Conceptually, rework brings the product back into full conformity with the released design definition (drawings, specifications, bills of material, and approved processes).
Typical characteristics:
- The nonconformance is eliminated and the part fully meets all drawing requirements and specifications afterward.
- No change to design intent or functional performance is accepted.
- Usually follows existing, approved manufacturing or inspection processes, or processes that can be validated and documented as equivalent.
- Normally does not require customer approval if handled strictly within your approved nonconformance procedures and contractual requirements. Some customers still require notification in specific cases.
- Traceability is required through NCR / MRB records, but the as-built configuration matches the released design after rework.
Examples:
- Re-machining a surface that was out of tolerance until the feature meets the print.
- Stripping and reapplying a coating to meet thickness or adhesion requirements.
- Re-running an assembly step using the same work instruction to correct a mis-installed hardware item.
Key risk if misused: Calling something “rework” when the final condition still deviates from the design (even slightly) can create hidden configuration and conformity issues, especially in serialized or safety-critical hardware.
Repair
Conceptually, repair accepts a controlled deviation from the released design and restores functional suitability, but not full design conformity. The product is made usable, but its condition is different from the baseline design definition.
Typical characteristics:
- The final condition remains out of strict design specification but is judged acceptable via engineering analysis and defined repair instructions.
- Usually requires engineering authority (e.g., design engineering) to define and approve the repair.
- Often requires customer or design-organization approval and issuance of a concession or deviation, depending on contracts and regulatory context.
- Repair instructions are usually unique or limited-use processes that must be documented, version-controlled, and tied to specific parts/serials.
- Configuration and traceability records must clearly link the product to the approved repair, including any operational or maintenance limitations.
Examples:
- Blending a nick on a rotating part beyond drawing limits but within an engineering-defined damage tolerance envelope.
- Installing a bushing or oversize fastener to salvage an oversize hole outside drawing requirements.
- Applying localized weld repair and machining in a way not defined in the original drawing or specification.
Key risk if misused: Treating repairs as routine production steps without appropriate engineering analysis, concession/deviation control, and traceability can cause long-term reliability issues and undermine airworthiness evidence.
Use-as-is
Conceptually, use-as-is accepts the nonconforming condition with no physical change, based on engineering assessment that the nonconformance does not adversely impact fit, form, function, safety, or regulatory requirements.
Typical characteristics:
- The product remains as built and does not fully meet design requirements.
- An engineering or authorized body performs a documented assessment to justify that the deviation is acceptable.
- Frequently requires formal deviation or concession and, in many aerospace contracts, customer approval.
- Must be traceable to the specific serial/lot, with clear documentation of the accepted discrepancy.
- May trigger additional inspection, monitoring, or maintenance instructions, depending on consequence of failure.
Examples:
- A minor cosmetic defect on a non-appearance-critical surface where design requirements were conservative, and engineering confirms no impact.
- A slightly undersize chamfer whose deviation is shown by stress or tolerance analysis to be acceptable.
- A non-critical dimension out of tolerance on a non-load-bearing feature that does not affect interfaces or assemblies.
Key risk if misused: Overuse of use-as-is to avoid rework/repair costs can degrade fleet reliability and exposes gaps in design margin understanding, especially if trend data on repeated use-as-is decisions is not analyzed.
How AS9100 treats these dispositions
AS9100 does not redefine basic quality terms, but it requires you to control nonconforming outputs, including how you:
- Identify and segregate nonconforming product.
- Define and enforce authorized dispositions (rework, repair, use-as-is, scrap, etc.).
- Obtain necessary approvals, including customer and design-authority approvals when required.
- Maintain records to demonstrate traceability, risk assessment, and conformity to approved dispositions.
The standard also expects that where the product does not meet requirements specified by the customer or applicable regulations, you will not repair or use-as-is without prior authorization from the applicable authority (e.g., customer, regulatory holder, design organization), in line with contracts and regulatory constraints.
Practical decision boundaries
A simple way to distinguish the three in daily operations is:
- Rework: After action, the product is indistinguishable (by requirements) from fully conforming hardware. No change to specification or drawing is needed.
- Repair: You modify the product so it does not meet the original specification but is made fit for use by an approved engineering change or concession.
- Use-as-is: You do nothing to the product; you accept the deviation based on documented engineering and, where applicable, customer approval.
In a robust QMS, these boundaries are codified in procedures, MRB charters, and training, with clear rules for when customer or design-authority involvement is mandatory.
Dependencies on your environment and systems
How these dispositions actually work in your plant depends heavily on:
- Design authority and contracts: Whether you hold design approval or are a build-to-print supplier strongly affects when you can approve repair or use-as-is versus when customer authorization is required.
- QMS maturity: Weak NCR / MRB processes often blur the line between rework and repair, or treat use-as-is as an informal shortcut instead of a controlled concession.
- System landscape: In brownfield environments with mixed ERP, MES, PLM, and QMS tools, nonconformance dispositions often live in multiple systems. Misalignment can cause:
- ERP showing a part as conforming while PLM or QMS records a repair or use-as-is concession.
- Maintenance and MRO systems not seeing repair-specific limitations because NCR data is not integrated.
- Inconsistent serial-level genealogy, making it hard to answer audit questions about which units were repaired or accepted use-as-is.
Because replacing core QMS, MES, or PLM systems in aerospace can be highly disruptive and expensive, many plants overlay digital workflows on existing tools to standardize how rework, repair, and use-as-is are captured and approved, instead of attempting a full rip-and-replace.
Common pitfalls and controls
Some recurrent issues and mitigating practices include:
- Mislabeling repairs as rework: Control with MRB checklists that explicitly ask whether the final state meets all drawing and specification requirements.
- Informal use-as-is decisions: Require written engineering justification and, where applicable, evidence of customer approval before closing the NCR.
- Poor traceability: Ensure serial/lot tracking links to NCRs and concessions so audit trails can show which units were reworked, repaired, or accepted use-as-is.
- No feedback into design and process improvement: Analyze trends in rework, repair, and use-as-is to feed corrective actions, design changes, and process improvements.
In all cases, the structure and rigor of your dispositions should be proportionate to risk, regulatory expectations, and customer contracts, not just cost and schedule pressure.
