Engineering change order (ECO)

Once a design is in production, any change (a new part, a drawing update, a firmware version) ripples into purchasing, inventory, tooling, test, documentation and possibly certification. An ECO records what changes, why, which units are affected (from which serial number or date), what happens to existing stock, and who approved it.

Revision control on drawings, BOMs and firmware is the backbone: everyone must be building to the same revision.

Where it bites: informal changes ("just swap that capacitor") lead to mixed builds, untraceable field failures, and certifications that no longer match what ships. Changes to radios, antennas, power supplies or safety-critical parts can require re-testing or new certification.