NANYANG TECHNOLOGICAL UNIVERSITY

Aircraft Maintenance and ReliabilityN. Satheesh (081854E15) Loke Jun Jie (081726G15)

Table of Contents

1 1.1 1.2 1.3

Introduction .......................................................................................................... 1 Early maintenance philosophy ........................................................................ 2 Redundancies as a safety net ........................................................................... 3 Development of the MSG ............................................................................... 4

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MSG-2 Maintenance approach ......................................................................... 11

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MSG-3 Maintenance approach ......................................................................... 14

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Comparison between MSG-2 and MSG-3 ........................................................ 16

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Development of a maintenance programme. ................................................... 17

5.1 5.2 5.3

MSI Selection ................................................................................................ 19 MSI Analysis Process.................................................................................... 19 Application of MSG-3 ................................................................................... 19

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Conclusion ........................................................................................................... 21

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References............................................................................................................ 22

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Introduction

The Wright flyer (refer to Figure 1(a)) was the first powered heavier than air aircraft which made its first flight on 17 December 1903. During the early days, air travel was never a popular mode of transportation as the aircraft were capable of operating only at low altitudes, were noisy, required frequent refuelling and had an accident rate higher than train travel (Anderson, 2005). Although commercial flights for passengers gained popularity with the introduction of the Douglas DC-3 in 1936, tickets were priced out of the affordability of commoners.

Figure 1: Evolution of aircraft - (a) Wright flyer, (b) B737, (c) Comparison of B747 and B707

It was not till more than 30 years later, when the Boeing 747 (B747) aircraft was introduced into the market in 1969, that air travel became common. This marked the era of the jumbo-jets which had the capacity for as much as thrice as many passengers. The B747 could be configured to carry up to 550 passengers; more than twice that of the B707-320 (219 passengers). Figure 1(c) offers a comparison in the size of the larger B747 with the B707.

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With the advent of these jumbo jets for air travel, came the requirement to make aircraft safer than ever before. In order to do so, the Boeing Company formed the Maintenance Steering Group (MSG) with inputs of representatives from airlines.

1.1 Early maintenance philosophyIn the early days, the typical maintenance programme would be developed by the aircraft manufacturer and provided to the airline. When the aircraft was brought in for maintenance, every component would be examined. These programmes were developed with the assumption that components would fail at a higher frequency as the aircraft aged since they are subjected to mechanical wear and tear. Components which are worn out result in failure and degrade safety. Therefore, to reduce the probability of mechanical failures, the maintenance intervals would have to be reduced so that the components could be maintained before it failed. Maintenance often involved replacement of worn components, leading to the Hard Life concept. Similarly, there was this belief that more frequent maintenance would improve the safety of the aircraft. The determination of maintenance intervals was almost never analysed scientifically, but based only on experience and intuition. Studies based on the data collected showed that several assumptions made were not entirely true. Regardless of the maintenance frequency of aircraft, there would be failures which cannot be entirely eliminated. For instance, frequent stripping and assembly of aircraft components would have a detrimental effect on its reliability associated with the after-installation of equipment (Gdalevitch, 2000). Furthermore, the design of old aircraft provided much less consideration for its maintainability during the design stage. This resulted in maintenance activities which were costly, time consuming and above all, prone to human errors.

Figure 2: Airliners in the 1950s - (a) Douglas DC-6 and (b) Lockheed Constellation

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In the period from 1950 to 1960, the Douglas DC-6 and Lockheed Constellation (Refer to Figure 2) dominated the market for airliners. Through the maintenance of these aircraft, it was found that failure of components could have been prevented, in many cases, through inspections at regular intervals when signs of failure are apparent. Such a concept is known to be On-Condition maintenance.

1.2 Redundancies as a safety netWith the increasing demand for power as the airliners grew in capacity, design of larger aircraft incorporating multiple piston engines became a popular choice. This configuration provided for a higher level of safety since the failure of a single engine would not lead to a complete loss of propulsion. The B747 are capable of remaining airbourne with the failure of an engine. Hence, the early notion that any failure of components/systems degrades the level of safety will no longer be accurate under all circumstances. Jet engines were introduced to provide propulsion in the 1960s. This effectively introduced many new components. The task of avoiding any occurrence of failure became increasingly arduous and not economically practicable since few failures have any significant influence on the safety of the aircraft (Krahenbuhl, 1978). Instead, the stage was set to improve the reliability while ensuring that maintenance costs are kept at a manageable level. The first studies on the reliability of hundreds of components began during this period to prescribe the required form of maintenance.

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1.3 Development of the MSGAs technology advanced, larger aircraft such as the B747 were introduced. The primitive maintenance programmes were no longer acceptable since the jumbo jets not only carried much more passengers, but also had systems which are considerably more complex. The higher performance expected of these aircraft also meant that the safety margins had to be reduced, thus leaving less room for errors. A further motivation for the development of improved maintenance philosophies lies in the concerns of airlines in the maintenance of aircraft. Given that the B747 would be three times the size of existing airliners at the time of its introduction, airlines are concerned that its maintenance would deem the B747 not commercially viable. Despite incorporating the maintainability of the components to have high priority in the design stages, it was deemed insufficient to avoid losses which were the result of maintenance costs. There was a need for another approach in maintaining the jumbojet. The Boeing Company, in 1968, invited representatives from airlines which were interested in acquiring the B747 into its design and maintenance programme groups. To account for the regulatory issues, the Federal Aviation Administration (FAA) representatives were also invited. This formed the philosophy of the MSG approach, which incorporates maintainability right from the design stage of the B747 aircraft. Much of the effort in the development of the MSG approach is credited to pioneers including Bill Mentzer, Tom Matteson, Stan Nowland and Howard Heap, all of whom are from the now-defunct United Airlines. Adaptation of the MSG The MSG approach used on the B747 proved to be successful. Hence, it was adapted, with slight modifications, to other aircraft such as the Concorde, DC-8/9/10, MD80/90 and B737/757/777 and named the MSG-2. European aircraft manufacturers made further modifications to the philosophy, which was then referred to as the EMSG. It was also applied to military aircraft and weapon systems by the U.S. Department of Defense (DOD) in 1975 and named as the Reliability-Centred Maintenance (RCM) approach.

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Maintenance Steering Group 2 (MSG-2)

The MSG-2 approach is process-oriented and focuses on the failure of the component. It analyses each component for the mode of failure and classifies it a primary maintenance process. Age reliability patterns published in Reliability Centred Maintenance (US Department of Defence, 1978) showed that only 11% of the items could possibly benefit from the Hard Time maintenance process in the MSG-2 approach. Despite being costly, overhauls performed at inappropriate intervals can potentially reduce reliability. This led to the development of the On-condition maintenance process. There are components which are not suited for the Hard Time or On Condition maintenance processes. For instance, electronic systems often comprise of components which will not exhibit signs of wear prior to failure, nor can its life expectancy be predicted with any degree of accuracy. Such components would thus be maintained using the Condition Monitoring maintenance process. The Condition Monitoring process utilises reports by on-board data systems, flight crew and ground test equipment to predict the onset of failure. Maintenance Steering Group 3 (MSG-3) A further refinement of the MSG-2 approach in 1979 with inputs from parties such as the FAA, CAA, airlines, manufacturers of engines and aircraft and the U.S. Navy resulted in the development of the MSG-3 approach. The MSG-3 approach, in contrast with the MSG-2 approach, determines the maintenance tasks required to prevent failure of the system and not the individual components. This maintains the inherent level of reliability of the system. The focus is on the consequence of the system failure instead of the failure itself. It represents a new approach towards scheduled maintenance from both the analytical and practical viewpoints. Advantages of the MSG-3 approach are the increased flexibility in the development of the maintenance programme to take into consideration other factors such as economic and operational concerns. Maintenance programmes for modern aircraft such as the B777 and A330/340 have been developed under the MSG-3 maintenance philosophy. Despite the increased complexity of the modern aircraft systems, they are more easily maintained. This can only be attributed to on-board fault diagnoses systems such as the built-in test equipment (BITE). The B777 is one of the most maintainable aircraft and this is possible partially due to its onboard maintenance system (OMS).

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Figure 3- Overview of evolution of maintenance program

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Maintenance philosophies of the B777

Figure 4: Boeing 777 aircraft and its technologically advanced glass cockpit

The B777 aircraft (refer to Figure 4) is designed for maintainability and reliability as it would be definite that the cost of maintaining the aircraft would be more than its initial purchase cost. Having the maintainability factor as a priority from its design stages is therefore essential. Maintainability ensures that maintenance could be performed with relative ease while reliability reduced the occurrence of failures and thus, the number of unscheduled maintenance. Despite the increased complexity of systems, the B777 aircraft is known to be maintained with relative ease and at lower costs. In the design of the B777, systems are more technologically advanced than earlier airliners. Many of the mechanical components made way for digital systems. The disadvantage with the increased use of electronics lies in the challenge to prevent failures of digital systems. While mechanical components show signs of wear, digital electronic components would simply fail without noticeable signs which can be picked up during inspection. This also includes the integrated circuit (IC) chips on circuit boards and software which are embedded in systems. Furthermore, maintenance performed at regular intervals would not be able to prevent the failures and this renders the Hard Time approach not useful. Although it is conclusive that the transition of aircraft design towards digital avionics systems had improved the reliability of systems, there was still a pressing need to solve the problem of relatively high unscheduled removal. For instance, the ratio of unscheduled removal rate of components to the number of removals due to confirmed failures (MTBUR/MTBF) is typically 0.33 to 0.5 (Knezevic, 1999). A high MTBUR/MTBF ratio is desirable as that represents higher reliability. Despite the

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increased system complexity, the ratio is maintained due to a corresponding increase in functionality and better software. In the viewpoint of safety as well as the operational economics, it is undesirable to perform unscheduled maintenance. Airlines need to operate the aircraft for as many hours as possible daily with a reasonable load factor and maintain an excellent ontime departures record to remain profitable. Unscheduled maintenance not only reduces the availability of the aircraft, but also leads to compensation costs for the passengers if the delay is extensive. The flight schedule may also be disrupted if there is no spare aircraft available. A comparison of the service schedule reliability shown in Figure 5 shows the superior reliability of the B777 aircraft. Since the maintainability of the B777 has been considered during its design stages, it is not surprising that its reliability is much better than the older MD-11 aircraft.

Figure 5: Comparison of service schedule reliability

Improving reliability and availability Reliability of the systems critical to flight is accomplished by numerous back-ups. Critical systems are often backed up by triple redundancies and this increases the availability of the aircraft by allowing the corrective action to rectify the failure of a system to be deferred in accordance to the minimum equipment list (MEL). Fault rectification of the failed system can then be carried out during an overnight stopover or at a convenient location where spares are available. The availability of an aircraft is dependent upon its maintainability. Maintenance may be required, for instance, between flights. Such transit checks on the B777 aircraft can be accomplished within a short period of time as computers are able to detect faults and maintenance areas can be easily accessed. The faults detected by the computers

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may be displayed to the mechanics in the form of maintenance messages. This allows the mechanic to identify the fault accurately in an expeditious manner. It also reduces maintenance costs by preventing the replacement of functioning components. Incorporating technology in maintenance One of the features which improve the maintainability of the B777 aircraft is the incorporation of BITE. The BITE reduces the number of hidden failures in systems. With the shift of systems towards a glass cockpit system, much more electronics are incorporated in aircraft systems. Though electronic components may be easier to repair than mechanical systems, its failure is often not evident and difficult to diagnose. Unlike mechanical devices, electronics do not suffer the effects of wear and tear. The BITE would thus allow faults to be detected easily. The BITE was designed into components for the purpose of simplifying maintenance. This is especially useful in digital avionics since the BITE software can directly interpret the signals for possible faults. BITE can record the symptoms of a fault and even has the ability to diagnose it. The event can then be displayed to the flight crew or maintenance personnel in the form of a code. With the introduction of the BITE, impending system failures may be detected and the probability of not diagnosing or misdiagnosing a failure is reduced. In addition to the accuracy in failure diagnosis, it also allows the maintenance to be accomplished within a shorter timeframe. If the failure is detected in-flight and reported by the flight crew, there is also a possibility that the line maintenance personnel can prepare for the necessary maintenance before the aircraft arrives at the gate. The Aircraft Information Management System (AIMS) was also introduced in the B777 aircraft design with the intent to enhance functionality and performance and reduce the airlines cost of ownership. It allows for the integrated modular avionics (IMA) concept, whereby common hardware are integrated to form a functional system instead of a single system itself. This essentially calls for a common standard, the ARINC 629, whereby the hardware and software communicates using a fixed standard. The AIMS integrates several functions such as the flight management, cockpit displays, on-board maintenance, airplane condition monitoring, communications management and information management. Advantages of the AIMS are the interchangeability of hardware from different manufacturers and the ability for the Line Replaceable Unit (LRU) concept to be implemented so that defective components of the system can be replaced quickly. This is very unlike the early design concepts whereby systems function as a whole and had to be repaired.

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Interchangeability of components also represents a decrease in its cost per function. For instance, liquid crystal displays (LCD) are used in the cockpit in lieu of analogue dials and indicators. When dials and indicators fail, the information which is to be displayed is lost. On the contrary, multifunctional displays allow the information from a failed display to be displayed on another LCD. This reduces the quantity of spares which has to be maintained for the purpose of replacement. Advantages in maintenance philosophy of B777 Overall, the AIMS has resulted in the improved despatch reliability through fault tolerant designs and the capabilities to defer non-critical defects, reduced spares cost through use of common parts, an on-board maintenance system (OMS) which handles events detected by BITE. The utilisation of multifunctional displays instead of mechanical gauges reduced weight while increasing reliability. Ultimately, the MTBUR/MTBF ratio will be increased by isolating hardware and software faults. A further feature in AIMS is its ability to isolate failures from the systems to ensure that the failures are isolated to allow the system to recover from the anomaly. Unlike the early maintenance philosophies, there has been a shift to incorporate technology into the maintenance of more complex aircraft systems. This ensures that the maintenance required remains economically and operationally viable and reliable. The B777 aircraft has demonstrated the importance of considering maintenance from the design stage in contributing to higher reliability and maintainability of the aircraft.

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MSG-2 Maintenance approach

MSG-2 is a process-oriented maintenance program which uses decision logic methodologies developed by the Air Transport Association of America. MSG-2 uses bottom up approach whereby each components or systems are filtered into one of the three maintenance categories (Figure 6): (1) Hard Time (2) On Condition, (3) Condition Monitoring.

Figure 6-MSG 2 Flow chart

Hard Time. Early generation of aircrafts maintenance program were based on this concept. This concept assumes that the reliability is inversely proportion to operating age. Hard time specifies a fixed number of cycles or time a given component is allowed to be used in an aircraft. Once the specified time has elapsed, the component has to be either overhauled or replaced. For example, turbine disks (Figure 7) have well defined operational service period after which has to be drawn out of service regardless of its serviceability.

Figure 7-Turbine Disk

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On condition. This maintenance model avoids estimating the hard time failure of the components and focuses on regular inspections aimed at identifying potential malfunctions prior they occur. The inspection request the removal or repair of the components on the condition that they do not conform to the defined performance standards or requirements. Say for example the fuel pump which can be used until its unable to deliver the flow rate for which its designed for. At this point, even though the pump itself is operation, it is no longer capable meeting its design intent, thus has to be replaced. Condition monitoring. Condition monitoring could either be a failure based maintenance process or an anticipated process. This maintenance category is often used on components or systems that deteriorate over time.o

Failure-based monitoring. There are two processes which takes two forms under this name. In the first form, a component is allowed to be in service without any form of scheduled check till the component suffers from a functional failure. This form is avoided if the failure of the component could compromise the safety of the aircraft. For example, simply allowing an interior lighting bulb to burn out is perfectly acceptable in the first form of failure-based monitoring. On the contrary, permitting a turbine blade disk to failure mode is not acceptable. This will result in adversely affecting the safety of the aircraft and cascading damage can result in lengthy and costly repairs. The second form focuses on tasks that are specific in detecting hidden failures. This results in maximum economic and safe utilization of the component. However the form suffers from the following disadvantages:

Costly damage can occur to other items that make up the component or system. Usually the time to failure is an unknown variable, thus maintenance cannot be planned. This consequently leads to lengthy out-of-service time due to shortage of spares, materials and unavailability of specialist.

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Predictive monitoring. In this process, the deterioration of the component is closely monitored for symptoms of functional failure. To do so, parameters which are indicative of the deterioration or wear and tear are identified. Gathering the selected parameter and analysing them allows the accurate prediction of the components useful life (Figure 8). Predictive maintenance has the lowest cost and highest possible saving compared to other methods.

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This form of maintenance process is best illustrated by the monitoring the aircrafts engine(s). For an aircraft engine, parameters such as inlet pressure and temperature, N1 and N2 RPM, pressure ratio and EGT at various altitudes and Mach number is automatically logged by the onboard computer. These data can be extracted and the parameters of interest can be plotted against time. This plot can then be compared against known deterioration pattern so as to identify incipient failures. The accurate identification of failure well before actual occurrence minimizes costly and lengthy repairs while enhancing the safety of the aircraft and its occupants.

Figure 8-Predictive Maintenance Cycle

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3

MSG-3 Maintenance approach

MSG-3 is a task-oriented maintenance program specific aimed at overcoming the disadvantages associated MSG-2. It provides a decision flowchart which can be used as a basis to arrive at logical decisions. The decision flowchart is organized to reveal both evident and hidden defects and specifically designed to distinguish between safety related failures from economic failure in the design. MSG-3 also defined the necessary methodology for servicing and lubrication tasks. The MSG-3 differentiates safety-related failure from economic failure as shown in Figure 9.

Figure 9-MSG 3 Flow chart

Safety-related items. Any malfunction that could jeopardizes the safe operation of the aircraft or the safety of its occupants must be eliminated. To do so, the aircraft design must be robust enough that failure of any single device should not lead to catastrophic results. Therefore the current design practices provide sufficient tolerances to failure of critical components by providing redundancy, fault tolerance, fail tolerance and fail-safe features. These ensure that failure of a component or a system is mitigated while ensuring the safety of the aircraft. Under MSG-3, any component or systems malfunction which could adversely affect the airworthiness of the aircraft is defined to be a safety-related item. A 14

safety-related component suffering latent malfunction is treated differently from that suffers from apparent failure (Examples provided in Figure 10). Therefore MSG-3 maintenance methodology focuses the visibility of the malfunctioning component to define the subsequent tasks.

Figure 10-Latent and apparent failures

Potential economic impacts. If a malfunction of a component or system does not endangers the aircraft or the aircraft, then that failure can be classified to be an economic impact. Economic failures will not be result in the aircraft from being withdrawn from service and are usually rectified at during scheduled normal maintenance. Doing so ensures that the flight schedules are adhered without compromising on the safety aspects. MSG-3 defines economic malfunction as one that does not affect the airworthiness or the operation of the aircraft, however is economically undesirable due to high cost of repair. The analysis addresses issues such as high initial design, manufacturing and ownership cost, high maintenance cost, premature removal rates, significant access problems, and potential for mechanical dispatch delays.

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Comparison between MSG-2 and MSG-3

The differences between the MSG-2 and MSG-3 approaches is summarised and shown in Table 1. Consideration Maintenance costs and duration Economic Safety bias MSG-2 Bottom-up approach requiring more manpower MSG-3 Top-down process thus has decreased maintenance cost due to reduced maintenance tasks Pays little or no Clear distinction between consideration to economic safety related task from impacts of maintenance. economical tasks Heavily focused on the aircraft safety at any cost. Moreover does not identifies failure that are hidden to pilots Does not account for the Includes recent deterioration of structures developments in corrosion due to corrosion prevention of aircraft structures.Table 1-Comparsion between MSG-2 and MSG-3

Structural deterioration

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Development of a maintenance programme.

Developing a maintenance programme for a new aircraft is lengthy and financially taxing process. The process can take nearly three to five years to complete, thus it is often performed concurrently with the development of the aircraft. The current industrial practices favour the development of maintenance programs using the MSG3 methodologies while the MSG-2 has been completely phase out. Thus, this report will focus on the maintenance program development through the application of MSG3 philosophy. The outline of maintenance program development is illustrated in Figure 11. The maintenance requirements for new aircraft are developed from two distinct processes: Type Certification (TC) and Maintenance Review Board (MRB). The purpose of TC process is to ensure that the aircraft is capable of meeting the design intent while satisfying the regulatory standards. The MRB process consists of manufacturers, regulatory authorities, vendors and flight operators working in unison to create the maintenance requirements for the aircraft that is being developed. The maintenance requirement established by the MRB is published as Maintenance Review Board Report (MRBR). The MRBR is designed to be used by the aircraft operators in developing their customized airworthiness programme, which is subjected to regulatory authorities approval.

Figure 11-Process flow of aircraft maintenance program development

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MSG-3 is specifically intended in assisting the MRB in developing the initial maintenance program for a new aircraft. MSG-3 provides the guidance that is necessary in determining the maintenance requirements for the purpose of sustaining the useful service life of the aircraft and its power plants. The initial maintenance program can be tailored by the airline operators to facilitate efficient scheduled maintenance. The development of the aircraft maintenance programme through the application of MSG-3 consists of the following steps: 1. Identification of Maintenance-Significant Item (MSI) 2. Analysis of MSI to determine the function, operation, failure mode(s), failure consequence and other features of the design 3. Appropriate selection of maintenance tasks through the use of MSG-3 decision logic, which includes: Level 1 Analysis: Identification and examination of failure consequence. Level 2 Analysis: Selection of appropriate type of task according to the failure consequence identified by the level I analysis.

Figure 12-Maintenance task analysis process using MSG-3

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5.1 MSI SelectionNowlan and Heap (1978) specified that the first step in the development of the maintenance programme is the rapid but conservative selection of components or system which has significant functions. The report defined significant item as: the item whose failure could affect the operating safety or have major economic consequences. MSG-3 requires that the aircraft manufactures to provide the initial list of MSIs which has to be approved by the Industry Steering Committee (ISC). The selection of MSI is usually based on experience; however the emerging industrial practices recommend the use of IAEA-TECDOC-658 (1992) standards and methodologies.

5.2 MSI Analysis ProcessThe primary purpose of MSI Analysis process is to determine what happens when a functional failure occurs of the identified MSIs. The selected MSI items are then subjected to MSI Analysis process which uses Failure Mode and Effects Analysis (FMEA) methodology. FMEA is used to establish the cause-effect relationships, failure modes, consequences of functional failure of the items identified in MSI. It also includes the determination of local and system wide effects of an items failure and failure detection methods. By performing MSI analysis prior the application of MSG-3 decision logic will ultimately reveal the significance of a given failure to the aircraft as a whole.

5.3 Application of MSG-3To develop the necessary and efficient maintenance task, MSG-3s decision logic diagram is used extensively used during the maintenance program development. MSG-3 decision logic consists of two level analyses. The first level is used in identifying the nature of failure and its consequences. The second level is used for appropriate selection maintenance task according to the consequence of the failure identified by level 1 analysis. Two levels of analysis of MSG-3 Level I analysis evaluates if a given malfunction or a failure is evident to flight crew or if it is hidden. Malfunctions which are evident are further refined into two distinct categories malfunctions that undermines safety and those that affect operationally capability. Malfunctions affecting operational functionality are further separated into those that have economic impact and those that are not. All malfunctions that are 19

evident to the flight crew are number from 5, 6 or 7.Malfunctions having safety implications and hidden from the flight crew is classified either into safety or nonsafety related items. These are designated to be category 8 and 9 respectively.

Figure 13-Level I Analysis

Maintenance tasks addressing the function failure is identified through level II analysis. Both hidden and evident functional failures (cat 5 to 9 from level I analysis) are first accessed for lubrication and servicing. Thereafter the analysis of the flowchart follows through the path determined by the Yes answer. However for safety related failures (cat 5 and 8 from level I analysis), the design of flowchart is such that all questions raised along the flow chart has to be answered regardless of response to any given question. The last block of level II analysis requires further discussion. If the path through the flow chart results in this block for categories 6, 7 and 9, then the necessity for an alternative design of the component or the equipment has to be determined by the design engineering team. Such a task facilitates the development of the maintenance program of new aircraft or derivatives. This program will then by utilized by the maintenance engineer or the mechanics. In general neither the maintenance engineer nor the mechanic has the flexibility of redesign unless specified.

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Figure 14-Level II Analysis

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Conclusion

It is hardly intuitive that complex systems can be more easily maintained than those which are much more primitive. However, at least within the aviation industry, the trend seems to suggest that the statement is true. As compared to the aircraft developed in the early days, the latest aircraft has been designed with maintainability as an important consideration. Coupled with the incorporation of the latest MSG-3 maintenance philosophy, the maintenance cost of the aircraft represents a much smaller proportion of the operating costs than its predecessors. In addition, the accident rate has reduced ten-fold to three per million between 1960 and 2000; during which the MSG maintenance approach evolved. Without the development of a robust maintenance philosophy such as the MSG and utilising those developed in the past, the Boeing might never have sold its target of 400 B747 aircraft. Instead, it had since delivered 1427 B747 aircraft while large airliners such as the B777/787 and A380 continues to be popular. The latest variants of the B737 have incorporated the MSG-3 maintenance philosophy while manufacturers such as Boeing have extended the MSG-3 task-oriented philosophy to the older aircraft. It is thus without a doubt that the MSG-3 maintenance approach had contributed much to defining the commercial aviation of today and the future.

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ReferencesAnderson, J.D., 2005. Introduction to Flight. McGraw-Hill Higher Education. Gdalevitch, M., 2000. MSG-3, The Intelligent Maintenance [online]. Available from: http://www.aviationpros.com/article/10388498/msg-3-the-intelligentmaintenance [Accessed 9 February 2012]. Krahenbuhl, R., 1978. Maintaining Transport Aircraft. Aircraft Engineering, pp 413. US Department of Defence, 1978. Reliability-Centred Maintenance. San Francisco, California: US Department of Commerce. Knezevic, J. 1999. Chief mechanic: the new approach to aircraft maintenance by Boeing. Journal of Quality in Maintenance Engineering, 5(4), pp. 314-324. Kinnison, H.A., 2004. Aviation Maintenance Management. McGraw-Hill Professional. Jack Hessburg, 2005. Air Carrier MRO Handbook, McGraw-Hill Professional Massoud Bazargan, 2010. Airline Operations and Scheduling, USA: Embry-Riddle Aeronautical University

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