Why is there a mismatch between operation times in the planning systems and the times in reality?

Paper in proceeding, 2010

There is often a substantial difference between operation times in reality on the factory shop-floor and in the company’s planning and control system. This difference has several severe consequences for the company’s daily operation in terms of meeting delivery dates and utilizing the available resources in an efficient way, as well as more long term and strategic consequences for the company’s business. Offers to customers and investment decisions are based on the operation times in the planning system. There are three principal causes for the gap: Operation times are not set in a correct way from the outset, extra allowance time to handle temporary disturbances tends to become permanent and accumulate, and the fact that operation times once set in the planning system seldom are updated. The root cause for these three deficiencies is quite likely the management’s unawareness of the situation.