How do you decide whether a change requires partial or delta FAI?

There is no universal rule that fits every program or customer. The decision between a partial FAI and a delta FAI is driven by three things: the governing standard (AS9102 or equivalent), customer / contractual requirements, and your internal FAI and change-control procedures. Within those boundaries, the basic logic is to trace what changed and reverify only the characteristics and process elements affected by that change.

Start from the governing requirements

Before deciding scope, confirm:

• Which revision of AS9102 (or other standard) applies.
• Customer-specific FAI or PPAP-like requirements, including any mandated triggers for full vs partial FAI.
• Contract or PO language that may override your internal practice (for example, requiring full FAI when drawing revisions change, regardless of impact).
• Your internal FAI procedure and how it defines initial, partial, and delta FAI, including required approvals.

If there is a conflict, customer and contractual requirements typically take precedence over internal practice, as long as they do not contradict the base standard.

When a partial FAI is typically required

A partial FAI is generally used when the form, fit, or function could be affected, but not all characteristics or operations are impacted. Typical triggers (subject to customer rules) include:

• Drawing, model, or specification revision that changes some, but not all, features.
• Process flow or work instruction changes that impact a subset of characteristics, operations, or setups.
• Significant NC/CAPA-driven changes where corrective actions modify methods, tooling, or parameters relevant to specific features.
• Tooling, fixture, or program changes that could influence dimensions, orientation, or repeatability for targeted features.
• Material or source changes that may affect mechanical, thermal, or surface performance for certain characteristics only.

In a partial FAI you:

• Use the current FAI format (e.g., AS9102 forms) for the part.
• Identify only the characteristics and records impacted by the change.
• Reverify and document those items, referencing the baseline (initial) FAI for unchanged characteristics.

Unchanged characteristics are typically not re-measured but must still be traceable back to a previously accepted FAI package.

When a delta FAI is typically sufficient

In practice, many organizations use the term “delta FAI” for an even narrower scope than a formal partial FAI. This is usually appropriate when:

• The change is extremely localized (e.g., a single dimension, tolerance, or note clarified without impacting related features).
• A previously nonconforming characteristic has been corrected with no changes to the rest of the design or process.
• A minor CNC program tweak, offset change, or fixture adjustment affects one or a few dimensions only.
• Minor gage or method change affects how one characteristic is measured, not its underlying process capability.

In a delta FAI you typically:

• Document only the specific characteristics that changed or were corrected.
• Reference the last accepted (initial or partial) FAI package as the baseline.
• Show clear traceability from the change record (ECO, deviation close-out, CAPA) to the updated characteristic results.

Some customers do not formally distinguish between “partial” and “delta” and expect any reduced-scope activity to follow their partial FAI rules. In those cases, treat delta FAI as a subcategory of partial FAI and align with their terminology to avoid audit issues.

Risk- and impact-based decision process

Most robust procedures use a structured impact assessment to decide whether you need full, partial, or delta FAI. A practical approach is:

1. Identify the change driver
   Examples: drawing revision, model update, new material, process change, machine move, NC/CAPA, new supplier, or significant lapse in production.
2. Map the change to affected items
   Using ECN/ECR, PLM, or configuration management, determine which of the following are touched:
   • Design characteristics (dimensions, GD&T, material specs, surface requirements).
   • Manufacturing operations, routings, or setups.
   • Tooling, fixtures, programs, or inspection methods.
   • Suppliers or special processes (heat treat, plating, NDT).
3. Assess potential impact to form, fit, function, or safety
   If there is any plausible impact, err toward at least a partial FAI unless the customer has explicitly waived it.
4. Define the FAI scope
   Based on the mapping:
   • Full FAI: major design change, new part number, new manufacturing site, or fundamentally different process path.
   • Partial FAI: multiple affected features, operations, or materials, but the part number and core design intent remain the same.
   • Delta FAI: tightly localized change or correction affecting one or a very small number of characteristics.
5. Document the rationale
   Record why you chose partial vs delta (risk, impact analysis, customer requirements) and get appropriate approvals. This is often what auditors ask to see.

Brownfield and system coexistence considerations

In mixed PLM/MES/QMS environments, the main risk is missing impacted characteristics because design, routing, and inspection data are spread across systems. To make reliable partial/delta FAI decisions, you need:

• Good configuration control so that the FAI is clearly tied to a specific drawing/model revision, routing, and work instruction set.
• Traceable ballooning and characteristic lists that link drawing items to operations, tools, and inspection plans, even if those live in different systems.
• Clear integration or at least stable reference IDs so that when an ECO hits the PLM, affected characteristics in MES or inspection software can be reliably identified.
• Robust change control so process or tooling changes outside PLM (for example, on the shop floor or at suppliers) still trigger a formal FAI impact review.

Trying to replace all core systems at once to “fix” FAI is usually impractical in aerospace-grade or similarly regulated environments due to validation, downtime, and integration risk. A more realistic approach is to tighten FAI and change-control linkages between existing PLM, QMS, and MES systems and then selectively digitize FAI forms and ballooning.

Common pitfalls in deciding partial vs delta FAI

Typical failure modes to watch for include:

• Treating all changes as paperwork-only and skipping the impact analysis, which can lead to missed FAIs and audit findings.
• Informal “delta” checks done on the shop floor without documentation or linkage back to the formal FAI package.
• Under-scoping partial FAI, for example updating one dimension but ignoring related datums, patterns, or GD&T that are indirectly affected.
• Over-reliance on tribal knowledge where a single engineer decides scope without a documented method or peer review.
• Ignoring supplier changes (special processes, raw material mills, outside machining) that should trigger partial FAI at the supplier or at incoming inspection.

Practical guideline to distinguish partial vs delta FAI

Within the constraints of your customer and internal procedures, a practical rule-of-thumb is:

• If the change affects multiple features, operations, or process steps, treat it as a partial FAI.
• If the change is constrained to one or a very small number of characteristics, with no ripple effects, a delta FAI is usually sufficient.
• If you are unsure about impact, or the part is safety-critical, default to the more conservative scope or obtain written customer concurrence on the chosen approach.

Ultimately, the decision must be backed by a documented impact assessment, consistent with AS9102 and customer-specific expectations, and traceable in your QMS.