TIMWOODS Waste #2: Inventory – The Cost of Holding Too Much or Too Little

How much excess stock is sitting in your hangars, warehouses, or systems — and how much time, cost, and risk does it tie up before it’s actually needed?

Inventory waste occurs when airlines hold more materials, components, or information than necessary, or when resources wait idle between processes. This type of waste often goes unnoticed, yet it ties up capital, occupies valuable space, and can slow operations. Some inventory, however, is necessary for critical repairs or compliance, and Lean aims to reduce only unnecessary or idle stock.

In Lean, waste refers to any activity or resource that does not add value to the customer or the process. For an introduction to the TIMWOODS types of waste, see our previous article.

Understanding Inventory Waste

Inventory waste in aviation appears whenever stock exceeds demand or waits unnecessarily before use. Examples include:

• Excess materials or components sitting unused: Items stored longer than needed tie up space, require handling, and do not add value until used.

• Equipment or tools stored but not immediately required: Idle tools or machinery consume space, may need maintenance, and do not contribute to productivity.

• Records or information stored unnecessarily: Paper or digital files kept longer than necessary slow access, create clutter, and increase management effort.

• Work in progress (WIP) waiting due to large batches: Partially completed work or items sitting idle between steps tie up space, equipment, and personnel. This applies only to avoidable waiting, not mandatory scheduled maintenance dictated by regulations. Reducing batch sizes can help detect discrepancies earlier while maintaining operational efficiency.

The Hidden Cost of Excess Inventory

It might seem that bulk purchasing or storing large quantities protects against shortages. However, excess inventory has hidden downsides:

• Delayed defect detection: Issues may remain unnoticed in large batches.

• Accumulating inefficiencies: Large batches can create a “death spiral” where delays, quality issues, and inefficiencies slow overall progress.

• Resource drain: Storing, handling, and monitoring surplus items require ongoing effort and costs without adding operational value.

A batch is optimal if it improves the system rather than just a single stage. Some batching is necessary, but it should be carefully balanced to avoid overstocking while maintaining operational flow.

Inventory Waste and Lean Strategies in Aviation

Lean principles encourage Just-in-Time (JIT) inventory, an approach where materials or tasks are supplied only when needed — neither too early nor too late — to reduce excess and improve efficiency.

Pull strategies

Work and materials are triggered by actual demand, such as urgent repairs, unscheduled maintenance, or rectifying defects. This ensures resources are used efficiently and reduces idle inventory.

Push strategies

Some tasks must be planned in advance, such as scheduled maintenance, preventive component replacements, or aircraft modifications. Spare parts and materials are stocked based on forecasts to ensure aircraft are ready for planned flights and comply with safety regulations.

Airlines therefore use a hybrid approach. Pull strategies manage immediate operational needs, while push strategies ensure planned and regulatory activities are completed. Predictive maintenance, accurate planning, and supplier coordination help balance inventory levels, minimizing unnecessary stock while ensuring critical materials are available for repairs and operational reliability is maintained.

Reducing Inventory Waste in Practice

Airlines can minimize inventory waste with practical approaches:

• Implement JIT and demand-driven ordering: Stock materials and spare parts only when needed, reducing excess inventory and storage costs.

• Digitize maintenance and operational records: Reduce physical storage and improve access to information, eliminating idle inventory in the form of unnecessary records.

• Optimize batch sizes: Limit work-in-progress waiting between steps by balancing batch sizes, ensuring resources aren’t tied up unnecessarily.

• Collaborate with suppliers: Improve delivery reliability and flexibility to avoid overstocking while ensuring materials arrive when required.

• Maintain visibility of inventory: Keep a clear overview of spare parts, tools, and equipment to minimize excess stock while ensuring essential items are available for operational use.

Reflection

Consider your organization:

• How often do components or information sit idle before they are needed?

• Are there items in storage that could be eliminated or managed digitally?

• Could batch sizes or ordering policies be adjusted to improve system-wide efficiency rather than local convenience?

Inventory waste is a silent but costly part of airline operations. By adopting Lean strategies such as JIT, optimized batch sizes, and digital workflows, airlines can reduce storage costs, improve operational efficiency, and ensure critical resources are available when truly needed.

Learn to identify and reduce waste with Lean principles →