Aerospace structures typically require very close tolerances to be maintained across large assemblies. It is often not possible to produce components accurately enough for them to be fastened together to form the final assembly. Instead an accurate jig is normally used to hold components in their correct positions and any gaps or clashes between components are then shimmed or fettled.
The conventional approach of shimming or fettling within a jig leads to time consuming reworking of components at a late stage of assembly where a high level of capital is being tied up. Measurement assisted determinate assembly (MADA) uses measurements of components to predict gaps and clashes before actual assembly is carried out. It is then possible to rework components allowing part-to-part assembly.
In general large components are measured and smaller bridging components are machined to interface with the less well dimensionally controlled larger components.
