Technical notes

Delta FAI: from a design change to a reviewable inspection scope

Use the changed model as evidence for a review, not as the entire inspection decision.

Reviewed 1 October 2026

Establish the earlier baseline

Keep the approved design revision and its inspection record together. Record why the new review was requested. A CAD edit, tooling change or manufacturing change may trigger different questions; some of those questions cannot be answered from model geometry.

Identify the affected requirements

Compare the current and previous models, then review their characteristics. Check changed nominal values and tolerances, datum references and the relationship between a requirement and the edited geometry. Treat missing PMI or ambiguous correspondence as unresolved rather than silently carrying a previous result forward.

Build the proposed re-inspection list

Create a characteristic-level list with the source reference, reason for review and proposed action. Include requirements discovered outside the model, such as process notes or customer instructions. Retain a separate list of unresolved items so they are not lost when filtering the main result.

Confirm the formal inspection scope

Delta FAI is a useful working term, but the contract and applicable first-article inspection requirements control the scope. The responsible quality team determines when partial or complete work is required. A geometry-change list does not make that determination automatically.

Keep preparation and acceptance separate

PartDatum FAI can help prepare the model-derived list and supported exports. Measured results, inspection method, nonconformance handling and approvals still need to be completed. Retain the comparison evidence with the final record so another reviewer can understand both the decision and its limits.

Sources and further reading