ERP should usually own enterprise planning, commercial, financial, purchasing, and inventory valuation records. MES should usually own shop-floor execution: electronic travelers, work instructions at point of use, operation status, labor and machine events, inspections, nonconformance capture, and as-built traceability. The split is not universal. In aerospace manufacturing, the important point is to define one system of record for each controlled data object and validate the integrations that move data between systems.
What usually belongs in ERP
ERP is typically the system of record for business planning and financial control. It commonly owns:
- Customer orders, contracts, demand signals, and program-level commitments
- MRP, purchasing, supplier orders, and planned material requirements
- Inventory balances at the enterprise level, inventory valuation, and cost accounting
- High-level routings, work orders, production orders, and planned dates
- Shipping, invoicing, revenue recognition, and financial close processes
Some aerospace ERP environments also hold routing steps, labor standards, inspection flags, or quality codes. That does not automatically mean ERP should control detailed execution. It may simply reflect legacy configuration, prior validation decisions, or integration limitations.
What usually belongs in MES
MES is typically where planned work is executed and where the production record is built. It commonly owns:
- Electronic travelers and operation-level execution status
- Released work instructions, operator prompts, and point-of-use data collection
- As-built genealogy by serial number, lot, batch, part revision, material, tool, and process step
- Labor, machine, test, inspection, and signoff events
- In-process quality checks, defect capture, rework routing, and nonconformance initiation
- Real-time WIP visibility and dispatching constraints
For aerospace, MES often becomes the practical source of execution evidence. That evidence still depends on disciplined configuration management, user access controls, time synchronization, validated workflows, and controlled changes to forms, routings, and instructions.
Where PLM and QMS usually fit
The ERP-versus-MES question is incomplete without PLM and QMS. PLM often owns product definition: CAD, engineering BOM, design revisions, approved specifications, and engineering change records. Depending on the site, PLM, ERP, or MES may own the manufacturing BOM and process plan, but that ownership must be explicit.
QMS often owns CAPA, formal nonconformance disposition, supplier quality workflows, audit records, and quality system procedures. MES may initiate a defect or nonconformance from the shop floor, but the formal disposition may live in QMS. If both systems maintain status, closure rules and audit trails need to be reconciled.
Common boundary decisions
Most aerospace manufacturers need clear rules for a few high-risk objects:
- Part master and revisions: Often sourced from PLM or ERP, then consumed by MES. Revision effectivity must be controlled.
- Work orders: Usually created or released from ERP, then executed in MES.
- Routings and operations: May originate in ERP or PLM, but MES usually controls the executable version used by operators.
- Inventory: ERP usually owns enterprise quantity and valuation. MES may own point-of-use consumption, WIP movement, and material traceability events.
- Quality records: MES often captures in-process evidence. QMS may own formal quality system workflows and dispositions.
- Inspection data: MES may capture results, while FAI packages, customer portals, or specialized inspection systems may also participate.
Brownfield reality
In brownfield aerospace plants, a clean separation is rarely available at the start. Legacy ERP, MES, PLM, QMS, inspection, maintenance, and data collection systems may all hold overlapping records. Full replacement is usually unrealistic because of qualification burden, validation cost, downtime risk, integration complexity, traceability obligations, change control, and long equipment lifecycles.
A safer approach is usually to define the target system-of-record model, then migrate one boundary at a time. That requires interface specifications, reconciliation logic, data ownership, exception handling, and documented change control. Without those controls, the plant may create duplicate records that disagree during production, inspection, shipment, or audit preparation.
Failure modes to avoid
The most common failure is making MES a second ERP or forcing ERP to behave like a shop-floor execution system. Both patterns create avoidable risk.
- Duplicate routings with different revisions in ERP and MES
- Operators using instructions that do not match the released engineering configuration
- Material consumed in MES but not reconciled to ERP inventory
- Nonconformances opened in MES but not visible to the formal QMS workflow
- Manual spreadsheet bridges that become uncontrolled production records
- Unclear ownership of inspection results, signoffs, and electronic records
The correct split is therefore less about software category names and more about controlled authority. ERP should plan and account for the business. MES should control and record execution. PLM should control product definition. QMS should control the quality system. The hard work is proving that the handoffs are complete, traceable, and maintained under change control.