6 Big Losses

Loss categories for systematic root cause analysis

The concept of the 6 Big Losses is used to systematically break down production losses. It subdivides the three main OEE loss areas—availability, performance, and quality—into more specific categories, creating a solid foundation for root cause analysis and targeted improvement measures.

Availability Losses

Availability losses are divided into:

• Planned Downtime Includes planned maintenance, setup/changeovers, or breaks.

• Unplanned Downtime Caused by technical malfunctions, missing personnel, or missing materials.

The distinction between planned and unplanned often leads to discussion in practice. You can learn more about this in our guide, Defining Downtime Reasons.

Performance Losses

These are subdivided as follows:

• Reduced Production Speed The machine runs below the maximum possible speed (Maximum Demonstrated Speed, MDS).

• Micro Stops Originally defined as very short downtimes under 30 seconds—typically relevant in discrete manufacturing.

Micro stops do not occur in continuous processes due to process inertia. Therefore, this category is excluded—turning the "6 Big Losses" into 5 Big Losses.

Quality Losses

Here we differentiate between:

• Startup Scrap Losses occurring during production startup—such as at the beginning of a shift or after a changeover. This also includes material losses due to quality sampling.

• Ongoing Scrap Defective products during steady-state production, e.g., parts out of tolerance or material rejected by quality control.

Even if scrap is later reworked or approved for special release—it still counts as a quality loss in OEE.

Overview

The 6 (or 5) Big Losses for continuous manufacturing processes at a glance:

These categories can be further subdivided with specific reasons and root causes. Assigning concrete reasons supports the analysis phase by helping to understand the causes of losses—so the right improvement actions can be identified.