One of the main fears of most reliability and maintenance engineers is that, at the time of actual need, the required spare part will not be available. This is commonly referred to as a stock out. Thus the goal of many reliability and maintenance engineers is to eliminate spare parts stock outs and remove this influence on total downtime. So how do you eliminate all stock outs?

The short answer is that you can't do this without tying up massive amounts of money that would be better used elsewhere. Even then, I am not sure that you could guarantee eliminating all stock outs. This would possibly require holding multiple units of every part in your plant. That's not viable. That's the truth.

What you can do is accept stock outs in areas where they have little or no impact or where a viable supply alternative exists. Then work to eliminate stock outs for items that really matter. To achieve this you need a considered evaluation and analysis of the likely demand, the data on hand, and the factors that influence these two. Of course we cannot predict all failures, so there is no certainty. However, by being disciplined in your review of the items that matter, and accepting stock outs for those that don't, you will achieve far better service levels from your spare parts inventories.

Phillip Slater is a leading authority on materials and spare parts management. He is a qualified engineer, an experienced operations and maintenance manager, a seasoned management consultant, and the author of four operations management books, including Smart Inventory Solutions, now in its second edition. www.PhillipSlater.com

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