Reliability-Centered Maintenance: A Success Story for the Engine Repair Process
Editors Note: To serve the interests of our readers, we try to include articles that reflect the perspectives of all levels of management and technical expertise. Many of our articles deal with very specific technical issues, provide tutorials on statistical methods, or deal with advances in the reliability, maintainability, and supportability disciplines. The following article illustrates that top-level leaders view reliability not as an end in itself but as the means of achieving some bottom-line goal, such as safety or mission success. In this case, the bottom line is force readiness. It is important for all of us who consider ourselves reliability practitioners to never forget that reliability is important only insofar as it serves the bottom line.
The RAC thanks General Babbitt and his staff for providing us with this article, written as General Babbitt was busily preparing for his retirement.
Military logistics is the profession of ensuring readiness. Todays logistics priorities will determine future success or failure. Our approach to solving the challenge of readiness is largely determined by the political and economic environment. The 1990s clearly demonstrated that predicting where the next conflict will erupt is guesswork at best. When that decade began, the world was recovering from the end of the Cold War. East Germany had announced the end of border restrictions, and the Berlin Wall - the Cold Wars most enduring icon - soon collapsed. Nobody suspected that a major theater war in the Persian Gulf was less than one year away.
The message is clear: be ready for anything. As professional logisticians, we cannot afford to be caught with our guard down. In times of peace and prosperity, we must assume that another Gulf War or Kosovo is just around the corner. Todays Air Force must get to the fight quickly and sustain operations with few people and limited resources in locations where little or no support is available.
To prepare ourselves for the events that may lie just around the corner, we can and must take steps today that will ensure readiness tomorrow. The first step is to focus on the logistics processes that maintain overall readiness. One of the most recent adaptations of this process-first approach resides in the world of aircraft engines. Engine availability - once cited as a reason for low readiness - has become a success story that every echelon of logistics can emulate. Additionally, these process improvements have been beneficial in maximizing engine system reliability and have led to reduced operations and support costs.
Engine Readiness Challenges
Engine maintenance is a complex and challenging business. It is the cornerstone of our ability to deploy aircraft on a moments notice anywhere in the world. The key to success is maintaining enough engines to sustain combat sorties and compensate for scheduled maintenance - commonly known as the war readiness engine (WRE) level.
Recently, however, the Air Force faced several challenges in maintaining WRE levels. First, the 1990s witnessed a spare parts shortfall that limited our ability to perform some scheduled maintenance. As a result, the Air Force temporarily expanded use limits of many engine components to ensure availability for flying operations. Although this was not our preferred long-term solution to engine readiness, it did maintain readiness.
Second, the operations tempo increased sharply, placing an even heavier burden on a smaller, less experienced engine maintenance workforce. To maintain an acceptable level of engine readiness using limited available resources, the Air Force migrated to performing On-Condition Maintenance (OCM). This meant that only acute maintenance issues could be resolved while engines were in the shop.
Although OCM provided engines, it didnt result in a reliable level of system performance to maintain our time on wing (TOW) standards. Although it solved the instant budget issue, it inevitably lead to a larger bill later on. The solution to realizing the inherent engine reliability and operating at the lowest real cost was found in something that had been a part of Air Force policy since 1985: Reliability-Centered Maintenance (RCM). Unfortunately, the circumstances of the day forced its abandonment.
Maximizing Engine System Reliability
Using the RCM principles of repairing what is broken on an engine during unscheduled maintenance and what will likely fail before a desired TOW time is essential to maximizing engine system reliability. With these principles, the Air Force realized several engine-related success stories (see Figures 1 through 3).
In 1998 RAF Lakenheaths F100-PW-229 engine availability was unusually low. Forty-four broken engines were sitting in the shop awaiting maintenance or parts, creating 22 engine holes for the flying squadrons. That represented over a third of the 126 engines assigned to Lakenheath. The wings ability to support a major theater war was in jeopardy.
A team made up of experts from Lakenheath, the engine depot maintenance facility at San Antonio Air Logistics Center, and Pratt & Whitney (the F100 series engine manufacturer), looked to RCM for a solution. Once maintenance efforts were focused on repairing or replacing components that would likely fail before the next scheduled removal, reliability numbers improved. For example, unscheduled engine removals (UER) for Lakenheath decreased from over 3 per 1,000 engine flight hours (EFH) to just over 1 per 1,000 EFH (Figure 1). At Cannon Air Force Base, another test site, reliability of the F110-GE-100 engine also increased significantly. In a demonstration involving 44 engines, UERs were reduced from more than 3 per 1,000 EFH to 1.5 (Figure 2). These test cases showed that performing predictable, scheduled maintenance maximizes engine reliability and reduces operating cost.
Figure 1: Unscheduled Engine Removals at RAF Lakenheath (Click to Zoom)
Figure 2: Unscheduled Engine Removals at Cannon AFB (Click to Zoom)
Figure 3: Unscheduled Engine Removals at Luke AFB (Click to Zoom)
Additionally, an RCM demonstration involving 39 F100-PW220 engines at Luke Air Force Base produced similar improvements in reliability. UERs at Luke fell from nearly 3 per 1,000 EFH to about 1.4 (Figure 3).
Financial Benefits for RCM
Simply put, reliable engines are cheaper to maintain. As the mean time between removal (MTBR) rate of engines increases, the cost per engine flight hour decreases. A MTBR rate of 1,000 EFH equates to about $600 per engine flight hour for a fighter engine. However, if the MTBR is reduced to 200 hours, the cost per flight hour increases to nearly $1,500 per hour. F100-229 Unscheduled Removals at RAFL
Additionally, an average unscheduled engine shop visit costs about $30,000 for material, labor, and support at Luke Air Force Base (excluding the costs of module overhaul, if required). For each unscheduled engine removal prevented, a level of cost avoidance is achieved. Following the Luke Air Force Base UER data to its logical conclusion, the Air Force avoided about
$480,000 in UER costs. As reliability is maximized in engines, the Air Force should experience significant reduction in engine operating costs. This lesson is pertinent to all echelons of logistics, not just engines. The Air Force is now developing plans to implement these improved engine-build standards throughout the major commands.
This RCM example tells a story of successful process improvement. The Air Force approached engine reliability from a longrange perspective and clearly demonstrated why RCM was the best solution. The RCM teams ability to succeed was a direct result of their ability to show an impact on readiness and do it on a nearly cost neutral basis. In the future, up-front investments of any kind must target readiness if theyre going to receive adequate support. The success of the Air Forces return to RCMbased engine maintenance, despite its initial costs, highlights a theme thats relevant throughout the acquisition and sustainment process - appropriate proactive maintenance can both reduce operating costs today and improved readiness tomorrow.