AbstractAvailability measures are given for a repairable system under minimal repair with constant repair times. A new policy and an existing replacement policy for this type of system are discussed. Each involves replacement at the first failure after timeT, withTrepresenting total operating time in the existing model and total elapsed time (i.e. operating time + repair time) in the new model. Optimal values ofTare found for both policies over a wide range of parameter values. These results indicate that the new and administratively easier policy produces only marginally smaller optimal availability values than the existing policy.