They should be marked in a clear, traceable, and consistent way that matches the governing drawing, specification, or customer requirement and is carried through to the related entry on Form 3.
In practice, that usually means the key characteristic is explicitly identified in the characteristic accountability used for the FAI, then documented on Form 3 with the same characteristic reference, the design requirement, the inspection result, and the applicable measurement method or evidence. If your organization uses balloon numbers, flag symbols, or a dedicated notation for key characteristics, that convention should stay consistent across the drawing review, ballooned print, inspection plan, and Form 3 record.
What matters most is not a specific visual style on its own, but whether an auditor, customer, quality engineer, or downstream reviewer can reliably answer these questions from the record:
- Which requirement was designated as a key characteristic?
- Where is that requirement located in the source design data?
- Which Form 3 line item corresponds to it?
- What result was recorded?
- What objective evidence supports the result?
A practical approach is to ensure each key characteristic entry on Form 3 is:
- linked to the exact drawing or specification characteristic number
- visibly identified using your approved internal convention if one exists
- recorded with the required result and units
- supported by traceable inspection evidence, including gage, CMM, test report, or other controlled source as applicable
- aligned to the correct revision of the design record and planning data
If a customer, prime, or internal quality procedure requires a specific identifier, column use, annotation method, or supplemental form, follow that requirement. There is no safe universal shortcut here. AS9102 execution often varies by customer flowdown, software configuration, and how the organization controls ballooning and inspection planning.
Common failure modes
- Marking a characteristic as key on the print but not clearly carrying that designation into Form 3
- Using inconsistent numbering between the ballooned drawing and Form 3
- Recording a result without showing the key characteristic designation in a retrievable way
- Relying on tribal knowledge or color coding in a spreadsheet that is lost when the record is exported or printed
- Mixing revision levels between drawing, inspection plan, and FAI package
- Assuming FAI software will infer the designation correctly without validation
In brownfield environments, this often breaks at the handoff points between PLM, ERP, MES, QMS, and standalone FAI or ballooning tools. If the designation for key characteristics is managed in one system but Form 3 is produced in another, mapping and synchronization need to be checked carefully. Full replacement of legacy tools is often not realistic because of validation cost, qualification burden, downtime risk, and long-established evidence chains. Controlled coexistence is usually safer than a forced rip-and-replace approach.
If your procedure does not define exactly how key characteristics must appear on Form 3, the right next step is to define and approve a standard method under document control, then validate that the method is followed consistently across programs and systems.
So the short answer is: mark them using your approved, traceable convention and document them on Form 3 so the designation, requirement, result, and evidence are unambiguous. If that linkage is not clear, the record is weak even if the measurement itself is correct.