Glossary

Aircraft on Ground (AOG)

Aircraft on Ground (AOG) commonly refers to an aircraft that cannot fly due to a technical, maintenance, or parts issue.

Core Aerospace Operations Execution Aerospace MES, Inventory Accuracy, and AOG Risk Reduction

Aircraft on Ground (AOG) commonly refers to a condition where an aircraft is unable to fly or return to service because of an unscheduled technical, maintenance, inspection, or parts-related issue that must be resolved first.

In aerospace operations, AOG is both an operational status and a priority condition. It is used to signal that restoring the aircraft to an airworthy, serviceable state has become urgent, often triggering expedited maintenance activity, parts sourcing, logistics coordination, engineering review, documentation updates, and approval workflows.

The term includes situations such as unexpected component failure, missing or delayed replacement parts, inspection findings, damage, or unresolved maintenance actions that prevent dispatch. It does not usually refer to routine planned downtime, scheduled heavy maintenance, or normal aircraft parking unless those situations have escalated into an unscheduled inability to return the aircraft to operation.

How the term is used in operations

AOG often appears in MRO, fleet maintenance, supply chain, and manufacturing support workflows as a high-priority event. Organizations may use the term to classify:

an aircraft currently grounded
an urgent maintenance work order or service request
a critical parts shortage tied to a grounded aircraft
an expedited logistics or supplier response
a priority escalation across maintenance, planning, and procurement teams

For example, an ERP, MES, or MRO system may flag an order as AOG when a required serialized part, repair action, or release record is blocking return to service.

Common confusion

AOG is often confused with general downtime or backlog. The difference is urgency and operational consequence. A machine outage in a factory is not usually called AOG unless the term is being used informally by analogy. In aviation, AOG specifically relates to an aircraft that is grounded or at immediate risk of being grounded.

AOG can also refer to the urgent response process around the event, not only the grounded condition itself. For example, teams may say they are handling an AOG shipment or an AOG order, meaning the shipment or order supports a grounded aircraft.

Manufacturing and supply chain relevance

In regulated aerospace environments, AOG events often expose dependencies across maintenance records, part traceability, inventory accuracy, supplier responsiveness, and document control. Because the issue is time-sensitive, organizations commonly need fast visibility into part availability, configuration, lineage, open nonconformances, and current work status across connected systems.

In most MES, a WIP location represents where work is being performed on an in-process unit or batch, while an inventory location represents where material is stored and available for future use or shipment. The distinction affects traceability, costing, and system integrations, and can blur in brownfield plants or poorly modeled routings.

How does better kitting visibility allow for lower safety stock?

Better kitting visibility does not magically remove the need for safety stock, but it can justify lowering buffers in a controlled way. When you can reliably see kit status, shortages, and consumption in near real time, you reduce uncertainty and response time, which are major drivers of safety stock. This only works if data quality, integration, and planning discipline are strong, and it must be adjusted gradually under change control.

What metrics indicate that WIP visibility is improving?

Improved WIP visibility shows up as more complete, timely, and trustworthy data about where work is, what state it is in, and what is blocking it. In regulated, brownfield plants, the most reliable indicators combine data quality (coverage, latency, accuracy) with flow stability, fewer surprises, and reduced manual reconciliation effort.

How do you measure success for a MES pilot focused on inventory accuracy?

Success in an MES inventory‑accuracy pilot is not just a higher percentage on a KPI slide. You need a clean pre‑pilot baseline, statistically sound stock checks, clear scoping of what the MES actually controls, reconciliation with ERP/MRP, and evidence that accuracy gains are stable, auditable, and achievable in day‑to‑day operations under real constraints.

Related Glossary

Service Bulletin

A formal notice issued by a manufacturer describing a known issue, update, or required service action for equipment or systems.

Scope Definition

A documented description of the boundaries, objectives, and inclusions of a project, system, or process in industrial operations.

Baseline

A defined reference point of approved data, configuration, or performance used to compare, control, and track changes in industrial operations.