First Article Inspection
First article inspection is the complete verification of the first good part to come from a new setup, against every requirement the drawing carries, before the production run is allowed to begin. It is the moment a shop proves that its process — the program, the tooling, the material, the setups and the machine — actually makes the part the drawing demands, rather than discovering that it does not halfway through a run of hundreds. The principle is as old as machining itself: check the first part so the rest need not be scrap. Industry has given it an acronym and, in regulated sectors, a rigorous form — but at its heart FAI is the discipline of proving the process once, completely, before trusting it many times. This entry sets out what a first article inspection covers, how it is run, and where it sits between the machine and the production lot.
What the inspection verifies
A first article inspection is deliberately exhaustive, and it is the opposite of the sampling that follows it. Where production inspection checks a fraction of parts against a handful of critical sizes, the first article checks one part against everything: every dimension on the drawing, every tolerance, every surface finish call-out, every thread, every note that imposes a measurable requirement. It verifies the material is the called grade, that heat treatment or coating was applied and certified if the drawing asks for it, and that special processes were done by approved means. Nothing is assumed from the setup that made the part; the part itself must answer for the whole process. This is what distinguishes the first article from a routine measurement: not a check of one feature but an audit of the complete part, characteristic by characteristic, against the drawing that is its contract.
Ballooning and the report
Because the first article must account for every characteristic without missing or double-counting any, the drawing is first ballooned: each dimension, GD&T frame, surface finish symbol and note is numbered in turn, so a part with forty dimensions, a dozen geometric call-outs and several finish requirements carries sixty or more balloons. The balloons map one-to-one onto the rows of the inspection report, each row listing the characteristic, its nominal value and tolerance, the value actually measured, the method that measured it, and its pass or fail verdict. The report is thus the drawing rendered as evidence — a reader can follow any balloon from the print to its measured value and its judgement. In aerospace and defence the format is standardised by the AS9102 forms, which carry the part and revision identity, the material and process certifications, and the full characteristic accountability in three linked sheets; in a general job shop the same logic holds in whatever report form the shop uses.
How the features are measured
The instruments that take the readings follow the features and their tolerances, exactly as the entries on measuring a feature and surface finish describe. Ordinary sizes are taken with callipers, micrometers and gauges; bores with bore gauges and pins; surfaces with a profilometer; and the form, position and profile call-outs of GD&T — the true positions, flatnesses, perpendicularities — are measured on a coordinate measuring machine, whose touch probe records points on the part and compares them to the nominal geometry. The CMM is the reference for the tolerances and geometry that hand tools cannot judge, and its feature labels are matched to the drawing’s balloons so the measured report reconciles with the print. Tight tolerances and geometric call-outs demand it; the looser ordinary sizes do not — the first article uses the full ladder of instruments, each applied where it can answer honestly.
When a first article is required
The trigger for a full first article is any change that could alter whether the part meets its drawing, and the classic list runs to nearly every meaningful event in a part’s life. A new part demands one, since nothing has yet proved the process. A design change that affects fit, form or function demands one, as does a change of process — a different machine, a different method, a revised CNC program. A change of source triggers it: new material, new supplier, new location, new tooling or inspection tooling. Even the passage of time can trigger it, for a job not run in years, on the grounds that the process that once worked cannot be assumed still to hold. Where only a single characteristic changed, many systems allow a partial or delta inspection that re-verifies just the affected balloons, keeping the proof while sparing the cost of re-measuring everything the change did not touch.
What it proves — and what it does not
The honest reading of a clean first article is that the process, on the day it was proven, made a part that met its drawing in every respect — and no more. It does not prove the process is in statistical control, that the same setup will hold across a long run, or that parts made later cannot drift as tools wear and machines warm; those are the concerns of accuracy and repeatability, process capability and the sampling that production calls for. FAI is a gate, not a guarantee. Its value is the gate itself: the error caught on the first article — a wrong offset, a misread revision, a material of the wrong grade — costs the rework of one part and a correction of the process, where the same error caught after a hundred parts costs a hundred parts’ scrap and the very rework that a clean process would have avoided. It is why the discipline belongs in every shop that runs more than one of a part: the first piece is the cheap place to learn what the process makes, and first article inspection is how a shop chooses to learn it there rather than in the middle of the run. In the end it is the quiet contract of CNC machining — the proof, offered before the run begins, that the process has already made the part right once.