Aging U.S. Air Force fleets have deterioration problems, resulting in increased maintenance workloads. Programmed depot maintenance (PDM) is significant, requiring 2,000 to 50,000 labor hours and material. Rand developed the PDM Capacity Assessment Tool (PDMCAT), applied it to the KC135 PDM process, with three alternative forecasts of future workload and two fleetsize scenarios, to inform aircraft availability and resource allocation decisions.