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Article Excerpt
We describe a series of projects at the US Coast Guard (USCG) Aircraft Repair and Supply Center (ARSC) that demonstrates the value of OR methodologies for efficient supply chain management. These projects provided critical decision support for planning various repair and maintenance activities at ARSC. The establishment of an OR cell within ARSC, with several new employees and interns hired for this purpose, demonstrates the sustainability of these OR initiatives. The projects have created a strong emphasis on data-driven planning at ARSC. Their quantifiable benefits include reductions in inventory by 20-70 percent for 41 critical parts; repair-cost savings of 10 percent by using maintenance information for component repair planning; a successful planning of the conversion/upgrade of the H65 aircraft, thus enhancing the safety and capability for Coast Guard missions; and a 50-percent increase in throughput of the H60 Program Depot Maintenance (PDM) line, resulting in a reduction in deferred depot maintenance from a peak of $23.6 M to $6.5 M. OR techniques have clearly been successful in transforming the culture at USCG's ARSC from a "data rich and knowledge poor" decision-support culture to an "OR ingrained" decision-making environment.
Key words: government: defense; inventory: applications, maintenance policies; military; cost effectiveness; reliability, availability.
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Today, the US Coast Guard (USCG) can truly claim to be "OR ingrained." Most of its project proposals require the submission of careful data analysis, model building, and optimization as backup material to the project proposal. This was not always true. While USCG has a reputation for outstanding operational success, its aeronautical engineering program, the Aircraft Repair and Supply Center (ARSC), needed to improve its efficiency. This paper describes a unique partnership between USCG and faculty and students at Purdue University to develop an analysis-based decision-making system that made these efficiencies possible.
US Coast Guard Missions
USCG, one of the nation's five armed services, is a military, multimission, maritime service within the Department of Homeland Security. Its core objectives are to protect the public, the environment, and US economic and security interests in any maritime region in which those interests may be at risk; these include international waters and America's coasts, ports, and inland waterways (http://www.uscg.mil). It has five fundamental responsibilities: (1) maritime safety, (2) maritime security, (3) maritime mobility, (4) national defense, and (5) protection of natural resources. USCG uses a variety of platforms to conduct its missions, including cutters and small boats on the water and fixed and rotary-wing (helicopters) aircraft in the air.
Its inventory includes approximately 200 aircraft; the number in operation fluctuates because of maintenance schedules. Major aviation missions include search and rescue, law enforcement, environmental response, ice operations, and air interdiction. Fixed-wing aircraft, such as the Lockheed Martin C-130 Hercules turboprop and the Dassault HU-25 Falcon jet, operate from large and medium air stations. Rotary-wing aircraft, which include the Eurocopter HH-65 Dolphin and the Sikorsky HH-60 Jayhawk helicopters, can operate from flight-deck equipped cutters, air stations, and air facilities. All aircraft are permanently assigned to a land-based air station, but can routinely deploy throughout the world as needed.
[FIGURE 1 OMITTED]
There are 26 air stations that are located throughout the US coast and are home to flight and maintenance crews, the aircraft, and thus services provided by USCG (Figure 1).
The nature of the missions varies based on the location of the air stations. In addition to routine missions, occasional events of national significance (e.g., Hurricanes Katrina and Andrew) create surges in demand for USCG services. These surge operations involve large-scale deployment of USCG aircraft; for example, over 18 HH-60 aircraft (about half of the HH-60 operational fleet) were involved in responding to Hurricane Katrina.
Logistics Network for Aircraft
USCG has over 200 aircraft, which it must keep airworthy, and thus available for flight crews to execute missions; this is crucial to its operational readiness, as is operating within budget constraints. ARSC operates as USCG's aviation logistics center, providing one-stop shopping for all aviation logistics support. It provides air stations with depot-level maintenance, supply, engineering, and information services to support the missions (http://www.uscg.mil/ hq/arsc).
As missions are defined and executed, they trigger a series of tasks involving the dispatching of aircraft from air stations to complete these tasks; this use results in aging of installed parts and component failures. In most cases, the air stations replace broken parts on the aircraft and send these broken parts back to ARSC to evaluate and repair locally or through outsourcing. In some cases, severe aircraft damage may require relocating the entire aircraft to ARSC for more complex repairs. Because the air stations are located in different climate regions, ranging from Miami, Florida to Sitka, Alaska, the impact of aircraft use on wear varies across air stations. ARSC, the main repair facility, thus receives broken parts, aircraft for overhaul, and requests for parts replenishment. It uses a combination of working-parts inventory, in-house repair, outsourced work, and contracts with suppliers to manage the repair process. ARSC also manages modifications of aircraft that undergo design changes, upgrades, and maintenance over time.
The ARSC repair and overhaul process follows a centralized control policy; a single facility in Elizabeth City, North Carolina serves as the focal point. ARSC owns the entire aircraft and parts inventory although it may deploy some inventory across air stations. In addition, ARSC provides information services that enable total asset visibility of parts anywhere in the system and the sharing of that inventory through parts-pooling. Thus, both components and aircraft may be moved across air stations to maintain mission coverage.
While individual air stations perform parts replacement and inspection, they depend on ARSC for individual component repair or overhaul and replacement, as well as for aircraft upgrades. Because aircraft and parts are shared across the network of air stations, a broken part received from one air station may well be sent to another--thus generating a mixing of parts and aircraft across the system.
Certain life-limited parts, such as mechanical gearboxes and engines, require overhaul at predefined intervals. In addition, to preserve the useful life of the aircraft, it also needs an overhaul periodically, principally to address any latent structural damage from fleet use and repair, and prevent corrosion damage from the salt water-laden operating environment. When ARSC receives parts, it may route them through different paths depending on decisions that the item manager (the person responsible for managing the item-level inventory) makes. If the entire aircraft comes to ARSC for an overhaul or an upgrade, it undergoes a program depot maintenance (PDM) process, which we describe in the Program Depot Maintenance (PDM) Process section, or a modification process. If a subassembly is returned, it may sit in inventory before being allocated for repair, or it may be sent immediately for repair. ARSC may perform some portion of the repair, send some (e.g., anodine metal treatment) to a supplier, and perform the final steps itself. ARSC selects the optimal combination of repair resources by evaluating performance and budget availability factors and executes contracts for repair services. ARSC tracked many of the parts using serial numbers; this stems from the need to manage life-limited or flight-safety critical parts. During its life cycle, a part may undergo design upgrades to improve its performance, provided that the aircraft manufacturer and USCG's configuration control board approve the upgrade. There may also be decisions regarding the extent of repair versus scrapping a part, such as a component or subassembly (e.g., bearing or gear), that is beyond economical repair or its service life. After some predetermined life limit, ARSC retires parts from its system and destroys them to prevent their reentry into the parts system. Tracking of...
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