A 2-MACHINE REPAIR MODEL WITH VARIABLE REPAIR RATE

A two-unit cold standby production system with one repairman is consid ered. After inspection of a failed unit the repairman chooses either a slow or a fast repair rate to carry out the corresponding amount of w ork. At system breakdown the repairman has an additional opportunity t o switch to the fast rate. If there are no fixed costs associated with system breakdowns, then the policy which minimizes long-run average c osts is shown to be a two-dimensional control limit rule. If fixed cos ts are incurred every time the system breaks down, then the optimal po licy is not necessarily of control limit type. This is illustrated by a counterexample. Furthermore, we present several performance measures for this maintenance system controlled by a two-dimensional control l imit rule.