The core purpose of the FAI is to 'use one part to represent all'—that is, using the first production part as a sample to verify whether the supplier's process capability, measuring equipment, and quality control records can be consistently replicated in subsequent batches. For OEM buyers and Tier-1 suppliers, passing the FAI means the process is frozen and mass production can begin; failing it means the process is not yet under control and requires rework or resubmission. When reviewing an FAI, buyers should treat it as evidence of the supplier's process maturity, not merely a dimensional report.

In practice, the most common deficiency in FAIs is not dimensional nonconformance but 'traceability breaks'—for example, missing material certificates, expired calibration dates on measuring equipment, unstated drawing revisions, or critical characteristics only sampled rather than fully inspected. Another common issue is 'data without judgments,' where buyers must interpret pass/fail themselves, increasing communication costs. When receiving an FAI, buyers should first check traceability completeness, then review dimensional data, and finally look at sign-offs—this quickly filters out suppliers that lack mass production capability.

Buyers can request an FAI template from the supplier during the quotation stage and specify the format (e.g., AS9102 or a custom template). If the buyer has their own FAI template, it should be provided in the RFQ to avoid rework after the supplier submits in their own format. For CNC machined parts, critical characteristics (KPCs) typically include dimensional tolerances, geometric dimensioning and tolerancing (GD&T), and surface roughness; these items must be listed individually in the FAI and cannot be omitted.