Development Of Maintenance Programs PDF

DEVELOPMENT OF MAINTENANCE PROGRAMS 1. Maintenance programs in commercial aviation are developed using two basic approaches: the process-oriented approach and the task-oriented approach 2. The differences between these two approaches include: a. Attitude toward maintenance actions....

DEVELOPMENT OF MAINTENANCE PROGRAMS 1. Maintenance programs in commercial aviation are developed using two basic approaches: the process-oriented approach and the task-oriented approach 2. The differences between these two approaches include: a. Attitude toward maintenance actions. b. Manner in which maintenance actions are determined and assigned to components and systems. 3. The commercial aviation industry has shifted to the task-oriented approach for newer airplane models, but older aircraft still use the process-oriented approach. 4. McDonnell-Douglas (now part of Boeing) and Boeing have developed new task- oriented maintenance programs for some older model aircraft, which operators can purchase from the manufacturer. 5. The process-oriented approach to maintenance uses three primary maintenance processes: a. Hard time (HT) - for components or systems with definite life limits. b. On-condition (OC) - for components or systems with detectable wear-out periods. c. Condition monitoring (CM) - for systems and components that cannot utilize HT or OC processes. CM items are operated to failure, and failure rates are tracked for prediction and prevention efforts. 6. The task-oriented approach to maintenance involves predetermined maintenance tasks to prevent in-service failures. Equipment redundancies may be used to allow in- service failures without compromising safety and operation. 7. Reliability programs, more elaborate than the CM process, are employed for components or systems with unpredictable failure rates and no scheduled maintenance tasks. 8. Reliability programs, more elaborate than the CM process, are employed for components or systems with unpredictable failure rates and no scheduled maintenance tasks. Maintenance Steering Group (MSG) Approach 1. Boeing initiated a modern approach to maintenance program development in 1968 with the Boeing 747, marking the start of a new era in aviation 2. Teams were organized, including representatives from Boeing, suppliers, airlines, and the FAA, to develop a more sophisticated maintenance program. 3. Six industry working groups (IWGs) were formed to address various aircraft systems, including structures, mechanical systems, engines and APU, electrical and avionics systems, flight controls and hydraulics, and zonal considerations. 4. Each IWG analyzed their respective systems, considering maintenance significant items (MSIs), failure modes, effects, and causes, using a logic tree to determine maintenance requirements. 5. The approach was called a "bottom-up" approach, focusing on components as likely causes of equipment malfunction. 6. Three maintenance processes were identified: Hard Time (HT), On-Condition (OC), and Condition Monitoring (CM). 7. This maintenance steering group (MSG) approach was successful on the Boeing 747 and was adapted for other aircraft, becoming MSG-2, which was also used for Lockheed L1011 and McDonnell-Douglas DC-10 airplanes. 8. This maintenance steering group (MSG) approach was successful on the Boeing 747 and was adapted for other aircraft, becoming MSG-2, which was also used for Lockheed L-1011 and McDonnell-Douglas DC-10 airplanes. 9. The process involved several steps, including identifying maintenance or structure items, functions, failure modes, and tasks, and assessing their applicability. 10. For structures, initial sampling thresholds were evaluated. 11. A simplified process flow diagram was used to assign maintenance processes to selected tasks based on safety-related factors and the availability of maintenance checks. 12. The frequency of maintenance actions was determined using available data on failure rates, removal rates, etc., for the item in question. Process-Oriented Maintenance 1. Process-oriented maintenance programs in aviation are developed using decision logic procedures created by the Air Transport Association of America (ATA). 2. The MSG-2 process is a bottom-up approach in which each unit on the aircraft (system, component, or appliance) is analyzed and assigned to one of the primary maintenance processes: HT, OC, or CM. 3. Hard time maintenance involves the removal of an item at a predetermined interval, typically specified in flight hours, flight cycles, or calendar time. 4. On-condition maintenance means that the item will be checked at specified intervals (in hours, cycles, or calendar time) to assess its remaining serviceability. 5. Condition monitoring entails monitoring failure rates, removal rates, and other parameters to aid in maintenance planning. 6. The text suggests that each of these maintenance processes will be explained in more detail. Hard Time (HT) Process 1. Hard time is a failure preventive maintenance process that requires removing an item from the vehicle and either completely overhauling it, partially overhauling it (restoring), or discarding it before exceeding a specified interval. 2. The hard time interval can be specified by various factors, including calendar time, engine or airplane check interval (e.g., engine change, "C" check), landing or operating cycles, flight hours, block hours, specified flights (e.g., over water, terminating), or in conjunction with another process like On-Condition (OC). 3. When Hard Time (HT) is specified, a component is removed from the vehicle and overhauled, restored, or discarded before exceeding the specified time interval. This restoration ensures reasonable assurance of satisfactory operation until the next scheduled removal. 4. Ideally, hard time is applied to components that consistently fail at a specific number of operating hours. This allows replacement before the component's failure, maximizing its useful life. 5. Hard time is also applied to items with a direct adverse effect on safety and to items subject to reliability degradation with age but without a maintenance check for that condition. 6. Components with safety concerns are not eligible for condition monitoring due to safety issues. 7. Some items, like rubber products, cannot be periodically checked for condition (no OC check), making hard time the appropriate maintenance process. 8. Examples of items controlled by hard time include structural inspection, landing gear overhaul, and replacement of life-limited engine parts. Mechanical linkages, actuators, hydraulic pumps, motors, generators, and similar items with defined wear-out cycles can also be identified as hard time items, depending on the operator's choice, as long as they are not safety-related. On-Condition (OC) Process 1. On-Condition (OC) is a failure preventive maintenance process that involves periodic inspection or testing of an item against appropriate physical standards (wear or deterioration limits) to determine its serviceability. 2. If an item fails an OC check, it must be overhauled or restored, at least by replacing out- of-tolerance parts, to ensure reasonable assurance of satisfactory operation for at least one additional OC check interval. If it cannot be restored, it should be discarded. 3. OC is applicable to components, equipment, or systems where continued airworthiness can be determined through measurements, tests, or other means without requiring a tear- down inspection. 4. OC checks must be performed within prescribed time limits and should provide meaningful determination of suitability for continued operation during the next check interval. 5. OC checks should measure or evaluate the wear and/or deterioration condition of the item and should not be mere maintenance tasks like servicing, adjustment, or a simple go/no-go determination. 6. Periodic data collection is part of the OC process, revealing the physical condition of a component, system, or engine. Analysis and evaluation of OC data help ascertain continued airworthiness, deterioration, and failure imminence. 7. OC data is directed to individual components, systems, or engines by serial number and can be used to predict decreasing life expectancy and failure imminence. 8. Examples of OC checks include tire tread and brake linings, scheduled borescope inspections of engines, engine oil analysis, and in-flight engine performance analysis (engine condition monitoring or ECM). 9. Many commercial airplane operators, especially in the United States, use the OC process to control engine overhaul based on engine data collected through ECM programs. 10. The key points to remember about the OC process are that it can maximize the life of components and engines if satisfactory checks ensure serviceability until the next OC check, and its applicability is limited by the need for satisfactory condition measurements or relevant failure prediction data. 11. Examples of components suitable for the on-condition process include brake wear indicator pins, control cables, linkages, control rods, pulleys, rollers, tracks, and jack screws, which are checked for wear, tension, diameter, play, or backlash. Condition Monitoring (CM) Process 1. CM is applied when neither the Hard Time (HT) nor the On-Condition (OC) process can be used for maintenance. 2. CM involves monitoring the failure rates, removals, etc., of individual components or systems that do not have a definite lifetime or noticeable wear-out period. 3. CM is not a failure preventive process like HT and OC, and there are no maintenance tasks to evaluate the life expectancy of CM items. These items are operated until they fail, and their replacement is an unscheduled maintenance action. 4. CM items must meet certain conditions, including having no direct adverse effect on safety when they fail, no hidden functions affecting safety, and inclusion in the operator's CM or reliability program for data collection and analysis. 5. CM items typically exhibit a random failure pattern and have no predictable life expectancy. 6. CM is most appropriate for complex systems like avionics and electronics components and for items where failure prediction or replacement doesn't improve life expectancy. 7. CM systems consist of data collection and analysis procedures to make judgments about the safe condition of the vehicle. Data sources include reports by flight crews, on- board data systems, ground equipment checks, and various maintenance data. 8. CM can also be used on HT and OC components to verify or adjust their intervals based on data collected over time. 9. CM data can indicate whether components are being monitored under the most appropriate process. 10. CM primarily monitors the failure or removal statistics of units rather than their actual condition, which is the focus of the OC process. Task-Oriented Maintenance 1. Task-oriented maintenance programs in aviation are developed using decision logic procedures created by the Air Transport Association of America. 2. The MSG-3 process is a modification and improvement upon the MSG-2 approach. 3. MSG-3 is a top-down consequence of failure approach, focusing on failure analysis at the highest management level of airplane systems, rather than at the component level as in MSG-2. 4. MSG-3 logic is used to identify suitable scheduled maintenance tasks with the goal of preventing failures and maintaining the inherent level of reliability of the system.v 5. Three categories of tasks are developed by the MSG-3 approach: a. Airframe system tasks b. Structural item tasks c. Zonal tasks Maintenance Tasks for Structural Items Sources of Structural Deterioration: 1. Environmental Deterioration: Physical deterioration of an item's strength or resistance to failure due to chemical interaction with its climate or environment. Environmental deterioration may be time-dependent. 2. Accidental Damage: Physical deterioration of an item caused by contact or impact with an external object or influence not part of the airplane. It can also result from human error during manufacture, operation, or maintenance. 3. Fatigue Damage: The initiation and propagation of cracks due to cyclic loading. Types of Structural Inspection Techniques: 1. General Visual Inspection: A visual examination aimed at detecting obvious unsatisfactory conditions or discrepancies. It may require removal of fillets, opening or removal of access doors or panels, and the use of work stands and ladders for access. 2. Detailed Inspection: An intensive visual inspection of a specified detail, assembly, or installation. It searches for evidence of irregularity using adequate lighting and, when necessary, inspection aids like mirrors, hand lenses, etc. Surface cleaning and detailed access procedures may be required. 3. Special Detailed Inspection: An intensive examination of a specific location. It includes special techniques such as nondestructive inspections (NDIs) like dye penetrant, high- powered magnification, magnetic particle, eddy current, etc. Disassembly of some units may also be necessary for this type of inspection. Zonal Maintenance Tasks Zonal Maintenance Program: 1. The zonal maintenance program ensures that all systems, wiring, mechanical controls, components, and installations within a specified zone on the aircraft receive adequate surveillance to determine their security of installation and general condition. 2. Type certificate (TC) and supplement type certificate (STC) holders use MSG-3 logic to develop maintenance and inspection series for zonal maintenance. Each zone analyzed is assigned a numerical reference. 3. Due to aging aircraft, the FAA has established specific damage tolerance criteria based on inspections in an aircraft operator's continued airworthiness program. 4. AC 120-93 provides detailed guidelines for damage tolerance inspection (DTI) for repairs and alterations affecting the fatigue-critical structure of the aircraft. It includes the area to be inspected, inspection methods and techniques, and inspection procedures. Inspection Level Techniques for Zonal Maintenance: 1. General Visual Inspection: A visual examination technique that covers multiple tasks generated against items in the system's maintenance program. It may involve tasks such as general visual inspections of multiple components within a zone. 2. Detailed Visual Inspection: An intensive visual inspection technique focused on a specific detail, assembly, or installation within a zone. This inspection method searches for evidence of irregularities and may require specialized lighting and inspection aids, like mirrors or hand lenses. Current MSG Process—MSG-3 1. The MSG-3 process was introduced in 1980 as a modification of MSG-2 by the Air Transport Association of America (ATA). 2. MSG-3 built upon the existing framework of MSG-2, which had been validated by a decade of reliable aircraft operation. 3. The MSG-3 process provides a more straightforward and linear progression through decision logic. 4. It is a top-down approach or consequence of failure approach, focusing on how the failure affects aircraft operation rather than individual components. 5. Failures under MSG-3 are categorized into two basic categories: safety-related and economic. 6. Maintenance tasks resulting from MSG-3 may include hard time, on-condition, and condition monitoring tasks, although they are not referred to by those terms. 7. MSG-3 allows flexibility in developing the overall maintenance program based on a logical analysis. 8. The MSG-3 process includes level I and level II analyses to determine maintenance tasks and intervals. 9. For evident failures, they are separated into safety-related and operationally related failures, with further categorization based on economic significance. 10. Hidden failures are categorized into safety-related and non-safety-related items. 11. If progression through the process ends up in a specific block for certain categories, it may lead to equipment redesign, especially for safety-related items. 12. Mechanics do not have the option of redesign unless indicated by the reliability program. 13. Working groups responsible for analysis receive information about systems, components, theory of operation, modes, failure modes, and relevant data. 14. They run through the logic diagrams, determine if failures are evident or hidden, assess safety and operational impact, and decide on maintenance tasks and intervals. 15. ATA's Technical Information and Communication Committee (TICC) incorporated ATA Spec 100 and ATA Spec 2100 into iSpec 2200, which is used in aerospace for standards in maintenance, technical documentation, and electronic exchange of aviation information. 16. iSpec 2200 aims to minimize costs among operators and manufacturers while improving information quality for operational needs. Maintenance Program Documents 1. The MSG-3 analysis results in the original maintenance program for a new model aircraft and is used by new operators of that model. 2. The selected maintenance tasks from the MSG process are published in the Maintenance Review Board Report (MRBR), an FAA-approved document. 3. The MRBR contains the initial scheduled maintenance program for U.S. certificated operators and is used by them to establish their FAA-approved maintenance program. 4. The MRBR includes the systems and power plant maintenance program, structural inspection program, zonal inspection program, aircraft zone diagrams, glossary, and a list of abbreviations and acronyms. 5. In addition to the MRBR, the manufacturer publishes its own document for maintenance planning, known by different names such as Maintenance Planning Data (MPD), On Aircraft Maintenance Planning (OAMP), or Maintenance Planning Document (MPD). 6. The MPD/OAMP document contains all maintenance task information from the MRBR and additional tasks suggested by the airframe manufacturer. 7. It sorts tasks in various ways to aid in planning, often grouping them by letter check and by hours, cycles, and calendar time. 8. Manufacturer's documents also include diagrams showing the location and numbering of access doors and panels, aircraft dimensions, and other information for maintenance program development and planning. 9. Man-hour requirements for each task are provided in these documents, but they are estimates and do not include time for activities like opening/closing doors, troubleshooting, or correcting discrepancies found during the task. 10. Maintenance intervals are defined to specify when maintenance tasks should be performed. Maintenance Intervals Defined 1. Aircraft maintenance work intervals depend on the aircraft manufacturer's standards and the operator's discretion, with various maintenance checks being named and defined in the MSG-3 process. 2. Maintenance checks are typically driven by Total Air Time (TAT) and Total Landing Cycles (CYC). 3. Airlines and aircraft operators are required to prepare a Continuous Airworthiness Maintenance Program (CAMP) under FAA oversight, outlining routine and detailed inspections commonly referred to as checks. 4. Standard intervals include Daily Checks, 48-Hour Checks, Hourly Limit Checks, Operating Cycle Limit Checks, and Letter Checks (A, B, C, D checks). 5. Daily Checks involve tasks like checking the oil level and addressing time-deferred maintenance items. 6. Hourly Limit Checks are determined by MSG analysis and assigned by the number of hours a unit or system has been operating. 7. 48-Hour Checks replace daily checks for most aircraft models and are performed every 48 hours, including more detailed tasks like wheel and brake inspection. 8. Operating Cycle Limit Checks are scheduled based on the number of operating cycles endured by specific airplane systems. 9. Letter Checks (A, B, C, D) were used in older aircraft models, while newer models like the Boeing 777 have eliminated letter checks in favor of scheduling tasks by hours or cycles for greater flexibility. 10. Operators may change basic maintenance intervals to address organizational needs, and this can be based on in-service experience, with proof of change typically collected through condition monitoring or reliability programs. 11. Maintenance intervals may need adjustments as aircraft age, with some intervals shortened and others lengthened to adapt to changing requirements. Maintenance is considered a dynamic process.