A simple general model for echelon overhaul and repair

In echelon overhaul and repair, failed or time-expired machines are removed and replaced by overhauled ones. The removed machines are sent to the rear echelon, typically the makerʹs works, to be overhauled to ‘good-as-new’. The paper presents a simple model for determining economic overhaul intervals in the presence of minor and major failures, PM and inspection of accessible and inaccessible components, and then goes on to consider how many machines should, for maximum long-term economy, be owned by the operator. The economic implications of an echelon policy for both the owners and the makers are briefly discussed. It is argued that simple models promply applied are often adequate for comparing competing systems and policies. An example involving gas-turbines in off-shore oil-rigs demonstrates the method generally, and in particular shows that the advantages may be dissipated if the overhaulers take too long to process overhauled machines.