As part of a hierarchical production control system, a policy is proposed for the admittance for new parts to a flexible manufacturing system (FMS) together with two different heuristics for dynamic routing of parts. The heuristics that consider the process plan's flexibility with respect to machines and operations are based upon operating time and machine reliability. To quantify flexibility, it is developed a priority type of the measurement considering machine's reliability that incorporates all the job and machine characteristics that contribute to routing flexibility. HUR which considers machine reliability is applied to drive some simulated systems and compared with the HUS using SPT rule. It is found that HUR outperforms HUS using SPT in terms of makespan and machine utilization.