Certification is evidence, not control
AS9100 Rev D provides a framework for controlling external providers, but certification does not prove controls are effective where the work happens. The IAQG is clear that AS9100 does not require flowing down the standard itself to every sub-tier supplier. Instead, each purchasing organisation decides which specific technical and safety requirements to communicate down the chain. In practice, flowing down critical technical requirements can often be the weak link.
Special processes such as heat treatment, non-destructive testing and surface finishing are often sub-contracted to lower tiers where direct oversight is difficult to demonstrate. Formal accreditations like NADCAP do not, by themselves, guarantee approved processes are followed consistently when delivery pressures are high. Similarly, First Article Inspection documentation under AS9102 may be completed, but subsequent changes to tooling, equipment, materials or location can often slip through re-validation unchecked. When drawing revisions and process parameters fall out of synchronisation across tiers, configuration management breaks down.
In short, whilst documentation is necessary, it is not always sufficient evidence of control.
Where the gap develops
In a multi-tier supply chain, the distance between design intent and manufacturing reality increases with every interface. Process transfers, tooling changes, material substitutions and commercial pressures introduce new sources of variation. Delivery incentives and
contractual delay penalties create powerful behavioural drivers at lower tiers, encouraging shops to defer secondary operations, adjust process parameters outside approved limits or avoid escalating non-conformances.
This is a familiar pattern of procedural drift when operational reality diverges from written requirements under the stress of a tight delivery schedule. The risk is magnified where sub-tier machine shops hold quality accreditations but lack deep aerospace experience.
