AVIATION MAINTENANCE MANAGEMENT BOOK
This is an okay overview of airline maintenance management. Some of the book is very repetitive. For example, every back shop (hydraulic, engine, etc) has a. Editorial Reviews. About the Author. Harry A. Kinnison, Ph.D., worked for the Boeing Company Highlight, take notes, and search in the book; Length: pages; Enhanced Typesetting: Enabled; Page Flip: Enabled. Kindle e-Readers. This unique resource covers aircraft maintenance program development and operations from a managerial as well as technical perspective.
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Co-written by Embry-Riddle Aeronautical University instructors, Aviation Maintenance Management, Second Edition offers broad, integrated. Technical Training; C. PART III: Aircraft Management, Maintenance, and . He developed this book because no suitable text for courses such as his existed. Items 1 - 6 Aviation Maintenance Management, Harry A. Kinnisonm Ph.D. to the publishers the idea of revamping the book and creating an even better.
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If you have not received any information after contact with Star Track, please contact us to confirm that the address for delivery logged with us are correct. It is simple: The maintenance of an air- craft provides assurance of flight safety, reliability, and airworthiness. The air- craft maintenance department is responsible for accomplishing all maintenance tasks as per the aircraft manufacturer and the companys requirements. The goal is a safe, reliable, and airworthy aircraft. The aircraft maintenance department provides maintenance and preventive maintenance to ensure reliability, which translates into aircraft availability.
These functions do not preclude a random failure or degradation of any part or system, but routine maintenance and checks will keep these from happening and keep the aircraft in good flying condition. Thermodynamics Revisited Nearly all engineering students have to take a course in thermodynamics in their undergraduate years.
To some students, aerodynamicists and power plant engineers for example, thermodynamics is a major requirement for grad- uation. Others, such as electrical engineers for instance, take the course as a necessary requirement for graduation.
Of course, thermodynamics and numer- ous other courses are required for all engineers because these courses apply to the various theories of science and engineering that must be understood to effectively apply the college learning to the real world.
After all, that is what engineering is all aboutbridging the gap between theory and reality. There is one concept in thermodynamics that often puzzles students. That concept is labeled entropy. The academic experts in the thermodynamics field got together one day as one thermo professor explained to create a classical thermodynamic equation describing all the energy of a systemany system. When they finished, they had an equation of more than several terms; and all.
They identified the terms for heat energy, potential energy, kinetic energy, etc. They were puzzled about the meaning of this term.
Aviation Maintenance Manegement
They knew they had done the work cor- rectly; the term had to represent energy. So, after considerable pondering by these experts, the mysterious term was dubbed unavailable energyenergy that is unavailable for use. This explanation satisfied the basic law of thermo- dynamics that energy can neither be created nor destroyed; it can only be trans- formed. And it helped to validate their equation. Let us shed a little more light on this. Energy is applied to create a system by manipulating, processing, and organizing various elements of the universe.
More energy is applied to make the system do its prescribed job. And whenever the system is operated, the sum total of its output energy is less than the total energy input. While some of this can be attributed to heat loss through friction and other similar, traceable actions, there is still an imbalance of energy. Defining entropy as the unavailable energy of a system rectifies that imbalance. The late Dr. Isaac Asimov, biophysicist and prolific writer of science fact and science fiction,1 had the unique ability to explain the most difficult science to the layperson in simple, understandable terms.
Asimov says that if you want to understand the concept of entropy in practical terms, think of it as the difference between the theoretically perfect system you have on the drawing board and the actual, physical system you have in hand. In other words, we can design perfect systems on paper, but we cannot build perfect systems in the real world. The difference between that which we design and that which we can build constitutes the natural entropy of the system.
A Saw Blade Has Width This concept of entropy, or unavailable energy, can be illustrated by a simple example. Mathematically, it is possible to take a half of a number repeatedly for- ever. Although the resulting number is smaller and smaller each time you divide, you can continue the process as long as you can stand to do so, and you will never reach the end. Now, take a piece of wood about 2 feet long a 2 4 will do and a crosscut saw.
Cut the board in half on the short dimension.
Then take one of the pieces and cut that in half. You can continue this until you reach a point where you can no longer hold the board to saw it. But, even if you could find some way to hold it while you sawed, you would soon reach a point where the piece you have left to cut is thinner than the saw blade itself.
When if you saw it one more time, there will be nothing left at allnothing but the pile of sawdust on the floor. The number of cuts made will be far less than the infinite number of times that you divided the number by two in theory. Asimov wrote over books during his lifetime. Why We Have to Do Maintenance 5. The fact that the saw blade has width and that the act of sawing creates a kerf in the wood wider than the saw blade itself, constitutes the entropy of this system.
And no matter how thin you make the saw blade, the fact that it has width will limit the number of cuts that can be made. Even a laser beam has width. This is a rather simple example, but you can see that the real world is not the same as the theoretical one that scientists and some engineers live in. Nothing is perfect.
The Role of the Engineer The design of systems or components is not only limited by the imperfections of the physical world i. A design engineer may be limited from making the perfect design by the tech- nology or the state of the art within any facet of the design effort. He or she may be limited by ability or technique; or, more often than not, the designer may be limited by economics; i.
Although the designer is limited by many factors, in the tradition of good engineering prac- tice, the designer is obliged to build the best system possible within the con- straints given. Another common situation in design occurs when the designer has produced what he or she believes is the optimum system when the boss, who is respon- sible for budget asks, How much will it cost to build this? Great, says the boss. Now redesign it so we can build it for under a thou- sand dollars.
That means redesign, usually with reduced tolerances, cheaper materials, and, unfortunately, more entropy. More entropy sometimes translates into more maintenance required. The design engineers primary concern, then, is to minimize not eliminate the entropy of the system he or she is designing while staying within the required constraints. The Role of the Mechanic The mechanic [aircraft maintenance technician AMT , repairer, or main- tainer], on the other hand, has a different problem.
Let us, once again, refer to the field of thermodynamics. One important point to understand is that entropy not only exists in every system, but that the entropy of a system is always increasing. That means that the designed-in level of perfection imper- fection? Some components or systems will deteriorate from use, and some will deteriorate from lack of use time or environment related.
Misuse by an operator or user may also cause some premature dete- rioration or degradation of the system or even outright damage. This deteri- oration or degradation of the system represents an increase in the total entropy of the system.
To summarize, it is the engineers responsibility to design the system with as high degree of perfection low entropy as possible within reasonable limits. The mechanics responsibility is to remove and replace parts, troubleshoot sys- tems, isolate faults in systems by following the fault isolation manual FIM, dis- cussed in Chap. Two Types of Maintenance Figure is a graph showing the level of perfection of a typical system.
One hundred percent perfection is at the very top of the y-axis. The x-axis depicts time. There are no numbers on the scales on either axis since actual values have no meaning in this theoretical discussion.
The left end of the curve shows the level of perfection attained by the designers of our real world system. Note that the curve begins to turn downward with time. This is a rep- resentation of the natural increase in entropy of the systemthe natural.
Natural decay of system increasing entropy. Time Figure The difference between theory and practice. Why We Have to Do Maintenance 7. When the system deteriorates to some lower arbitrarily set level of perfection, we perform some corrective action: That is, we reduce the entropy to its original level. This is called preventive maintenance and is usually per- formed at regular intervals. This is done to prevent deterioration of the system to an unusable level and to keep it in operational condition.
It is sometimes referred to as scheduled maintenance. This schedule could be daily, every flight, every flight hours, or every cycles a cycle is a takeoff and a landing. Figure shows the system restored to its normal level curves a and b.
There are times, of course, when the system deteriorates rather rapidly in serv- ice to a low level of perfection curve c. At other times the system breaks down completely curve d. In these cases, the maintenance actions necessary to restore the system are more definitive, often requiring extensive testing, trou- bleshooting, adjusting, and, very often, the replacement, restoration, or complete overhaul of parts or subsystems.
Since these breakdowns occur at various, unpredictable intervals, the maintenance actions employed to correct the prob- lem are referred to as unscheduled maintenance.
Scheduled maintenance c. Unscheduled maintenance. Point at which scheduled maintenance is done. Time Figure Restoration of system perfection. Reliability The level of perfection we have been talking about can also be referred to as the reliability of the system. The designed-in level of perfection is known as the inherent reliability of that system.
This is as good as the system gets during real world operation. No amount of maintenance can increase system reliability any higher than this inherent level. However, it is desirable for the operator to maintain this level of reliability or this level of perfection at all times.
We will discuss reliability and maintenance in more detail in Chaps. But there is one more important point to coverredesign of the equipment. Redesign Figure shows the original curve of our theoretical system, curve A. The dashed line shows the systems original level of perfection.
Our system, however, has now been redesigned to a higher level of perfection; that is, a higher level of reliability with a corresponding decrease in total entropy. During this redesign, new components, new materials, or new techniques may have been used to reduce the natural entropy of the system. In some cases, a reduction in man-. Designed - in level Reliability.
Time Figure Effects of redesign on system reliability. Why We Have to Do Maintenance 9. Although the designers have reduced the entropy of the system, the system will still deteriorate. It is quite possible that the rate of deterioration will change from the original design depending upon numerous factors; thus, the slope of the curve may increase, decrease, or stay the same.
Whichever is the case, the maintenance requirements of the system could be affected in some way. If the decay is steeper, as in B in Fig. The result is that maintenance will be needed more often. In this case, the inherent reliability is increased, but more mainte- nance is required to maintain that level of reliability level of perfection.
Unless the performance characteristics of the system have been improved, this redesign may not be acceptable. A decision must be made to determine if the perform- ance improvement justifies more maintenance and thus an increase in main- tenance costs. Conversely, if the decay rate is the same as before, as shown in curve C of Fig. The question to be considered, then, is this: Does the reduction of maintenance justify the cost of the redesign? This question, of course, is a matter for the designers to ponder, not the maintenance people.
One of the major factors in redesign is cost. Figure shows the graphs of two familiar and opposing relationships. The upper curve is logarithmic. It rep- resents the increasing perfection attained with more sophisticated design efforts.
Increase in perfection Is logarithmic Perfection. Increase in cost Is exponential. Figure Perfection vs. Stanley Nowlan and Howard F. Reliability-Centered Maintenance; U. The closer we get to perfection top of the illustration the harder it is to make a substantial increase. We will never get to percent.
The lower curve depicts the cost of those ongoing efforts to improve the system. This, unfortu- nately, is an exponential curve. The more we try to approach perfection, the more it is going to cost us. It is obvious, then, that the designers are limited in their goal of perfection, not just by entropy but also by costs. The combination of these two limitations is basically responsible for our profession of maintenance.
Failure Rate Patterns Maintenance, of course, is not as simple as one might conclude from the above discussion of entropy. There is one important fact that must be acknowledged: As you might expect, the nature of the maintenance performed on these components and systems is related to those fail- ure rates and failure patterns. United Airlines did some studies on lifetime failure rates and found six basic patterns. The vertical axes show failure rates and the horizontal axes indicate time.
No values are shown on the scales since these are not really important to the discussion. Curve A shows what is commonly referred to as the bathtub curve, for obvi- ous reasons.
This failure rate pattern exhibits a high rate of failure during the early portion of the components life, known as infant mortality. This is one of the bugaboos of engineering. Some components exhibit early failures for several. Stanley and Howard F.
Heap, Reliability-Centered Maintenance. Why We Have to Do Maintenance Once the bugs are worked out and the equipment settles into its pattern, the failure rate levels off or rises only slightly over time.
That is, until the later stages of the components life. The rapid rise shown in curve A near the end of its life is an indication of wear out. The physical limit of the components materials has been reached.
Curve B exhibits no infant mortality but shows a level, or slightly rising fail- ure rate characteristic throughout the components life until a definite wear-out period is exhibited toward the end. Curve C depicts components with a slightly increasing failure rate with no infant mortality and no discernible wear-out period, but at some point, it becomes unusable.
Curve D shows a low failure rate when new or just out of the shop , which rises to some steady level and holds throughout most of the components life. Curve E is an ideal component: Curve F shows components with an infant mortality followed by a level or slightly rising failure rate and no wear-out period.
The United Airlines study showed that only about 11 percent of the items included in the experiment those shown in curves A, B, and C of Table would benefit from setting operating limits or from applying a repeated check of wear conditions. The other 89 percent would not. Thus, time of failure or deterioration beyond useful levels could be predicted on only 11 percent of the items curves A, B, and C of Table The other 89 percent depicted by curves D, E, and F of Table would require some other approach.
They will not all come due for maintenance or replacement at the same time, however, but they can be scheduled; and the required maintenance activity can be spread out over the available time, thus avoiding peaks and valleys in the workload. The other 89 percent, unfortunately, will have to be operated to failure before replacement or repair is done. This, being unpredictable, would result in the need for maintenance at odd times and at various intervals; i.
These characteristics of failure make it necessary to approach maintenance in a systematic manner, to reduce peak periods of unscheduled maintenance. The industry has taken this into consideration and has employed several tech- niques in the design and manufacturing of aircraft and systems to accommo- date the problem. These are discussed in the next section. Other Maintenance Considerations The aviation industry has developed three management techniques for address- ing the in-service interruptions created by the items that must be operated to failure before maintenance can be done.
These are equipment redundancy, line replaceable units, and minimum aircraft dispatch requirements. The concept of redundancy of certain components or systems is quite common in engineering design of systems where a high reliability is desirable. In the case of redundant unitsusually called primary and backup unitsif one unit fails, the other is available to take over the function.
For example, in aviation most commercial jets have two high-frequency HF radios. Only one is needed for communications, but the second one is there for backup in case the first one fails.
A unique feature of redundant units also affects the maintenance require- ments. If both primary and backup units are instrumented such that the flight crew is aware of any malfunction, no prior maintenance check is required to indi- cate that incapability. On the other hand, if neither system is so instrumented, maintenance personnel would need to perform some check on both primary and backup systems at the transit or other check to determine serviceability.
Very often, however, one system usually the backup is instrumented to show serviceability to the crew. If a maintenance check is performed on the other i. In the case of fail- ure, then, they already have a positive indication, through the instrumentation, that the backup system is available and useable.
The purpose for this arrange- ment is to strike a balance between how much instrumentation is used and how much maintenance is required to ensure system serviceability. In some cases, the backup system is automatically switched into service when the primary system fails. Flight crew needs during the flight are primary concerns in making such decisions. Another common concept used in aviation is the line replaceable unit LRU. An LRU is a component or system that has been designed in such a manner that the parts that most commonly fail can be quickly removed and replaced on the vehicle.
This allows the vehicle to be returned to scheduled service without undue delay for maintenance. The failed part, then, can either be discarded or repaired in the shop as necessary without further delaying the flight.
The third concept for minimizing delays for maintenance in aviation is known as the minimum equipment list MEL. This list allows a vehicle to be dis- patched into service with certain items inoperative provided that the loss of func- tion does not affect the safety and operation of the flight. These items are carefully determined by the manufacturer and sanctioned by the regulatory authority during the early stages of vehicle design and test.
The manufacturer issues a master minimum equipment list MMEL which includes all equip- ment and accessories available for the aircraft model. The airline then tailors the document to its own configuration to produce the MEL more on this in Chap. Many of these MEL items are associated with redundant systems.
The con- cept of the MEL allows deferral of maintenance without upsetting the mission requirements. The maintenance, however, must be performed within certain pre- scribed periods, commonly 1, 3, 10, or 30 days, depending on the operational requirements for the system. The items are identified in the MMEL by flight crew personnel during the latter stages of new aircraft development.
Thus, flight personnel determine what systems they can safely fly the mission without or in a degraded condition. These flight crew personnel also determine how long 1, 3, 10, or 30 days they can tolerate this condition. Although this is determined in general terms prior to delivering the airplane, the flight crew on board makes the final decision based on actual conditions at the time of dispatch.
The pilot in command PIC can, based on existing circumstances, decide not to dispatch until repairs are made or can elect to defer maintenance per the airlines MEL. Maintenance must abide by that decision. Associated with the MEL is a dispatch deviation guide DDG that contains instructions for the line maintenance crew when the deviation requires some maintenance action that is not necessarily obvious to the mechanic.
A dispatch deviation guide is published by the airplane manufacturer to instruct the mechanic on these deviations. The DDG contains such information as tying up cables and capping connectors from removed units, opening and placarding cir- cuit breakers to prevent inadvertent power-up of certain equipment during flight, and any other maintenance action that needs to be taken for precau- tionary reasons.
This list provides information on dispatch of the airplane in the event that cer- tain panels are missing or when other configuration differences not affecting safety are noted.
The nonessential equipment and furnishing NEF items list contains the most commonly deferred items that do not affect airworthiness or safety of the flight of the aircraft. This is also a part of the MEL system. Although failures on these complex aircraft can occur at random and can come at inopportune times, these three management actionsredundancy of design, line replaceable units, and minimum dispatch requirementscan help to smooth out the workload and reduce service interruptions.
Establishing a Maintenance Program Although there has been a considerable amount of improvement in the quality and reliability of components and systems, as well as in materials and procedures, over the year life of aviation, we still have not reached total perfection. Aviation equipment, no matter how good or how reliable, still needs attention from time to time. Scheduled maintenance and servicing are needed to ensure the designed-in level of perfection reliability.
Due to the nature of the real world, some of these components and systems will, sooner or later, deteriorate beyond a toler- able level or will fail completely. In other instances, users, operators, or even maintenance people who interface with these components and systems can misuse or even abuse the equipment to the extent of damage or deterioration that will require the need for some sort of maintenance action.
We have seen that components and systems fail in different ways and at dif- ferent rates. This results in a requirement for unscheduled maintenance that is somewhat erratic and uncertain. There are often waves of work and no-work periods that need to be managed to smooth out the workload and stabilize the manpower requirements.
Those components exhibiting life limits or measurable wear-out characteris- tics can be part of a systematic, scheduled maintenance program. Design redun- dancy, line replaceable units, and minimum dispatch requirements have been established as management efforts to smooth out maintenance workload.
But there are numerous components and systems on an aircraft that do not lend themselves to such adjustment for convenience. It is necessary, then, that the main- tenance and engineering organization of an airline be prepared to address the maintenance of aircraft and aircraft systems with a well-thought-out and well- executed program.
The remainder of this textbook will address the multi-faceted process known as aircraft maintenance and engineering. The program discussed herein has been created over the years by concentrated and integrated efforts by pilots, airlines, maintenance people, manufacturers, component and system suppliers, regulatory authorities, and professional and business organizations within the aviation industry. Not every airline will need to be organized and operated in the same manner or style, but the programs and activities discussed in this text will apply to all operators.
Development of 2 Maintenance Programs. Introduction The maintenance programs currently in use in commercial aviation were devel- oped by the industry using two basic approaches: The differences in these two methods are twofold: Although the commercial aviation industry has recently gone to the task- oriented approach for the most recent airplane models, there are many older airplanes still in service whose maintenance programs were developed by the process-oriented approach.
In recent years, McDonnell-Douglas now part of Boeing and Boeing have developed new task-oriented maintenance programs for some of these older model aircraft. The operators can purchase these new programs from the manufacturer.
Aviation Maintenance Manegement
The process-oriented approach to maintenance uses three primary mainte- nance processes to accomplish the scheduled maintenance actions. The hard time and on-condition processes are used for components or systems that, respectively, have definite life limits or detectable wear-out peri- ods.
These are the items in categories A, B, and C discussed in Chap. The condition monitoring process is used to monitor systems and components that cannot utilize either the HT or OC processes. These CM items are operated to failure, and failure rates are tracked to aid in failure pre- diction or failure prevention efforts. These are the operate to failure items in categories D, E, and F of Table The task-oriented approach to maintenance uses predetermined maintenance tasks to avoid in-service failures.
Equipment redundancies are sometimes. A reliability program is usually employed similar to, but more elab- orate than, the CM process for those components or systems whose failure rates are not predictable and for those that have no scheduled maintenance tasks.
Reliability is discussed in Chap. Both of these maintenance philosophiesthe process oriented and the task orientedare discussed in general below along with the basic method of gen- erating the program. How the maintenance tasks and task intervals are deter- mined will be discussed in detail in later sections. The Maintenance Steering Group MSG Approach The Boeing Company started the modern approach to maintenance program development in with the Boeing airplane, then the largest commer- cial airplane.
It was the start of a new era in aviation, the era of the jumbo jets, and the company felt that this new era should begin with a more sophisticated approach to maintenance program development. They organized teams of rep- resentatives from the Boeing Companys design and maintenance program groups along with representatives from the suppliers and the airlines who were interested in buying the airplane.
The FAA was also included to ensure that reg- ulatory requirements were properly addressed. The process used involved six industry working groups IWGs: Each group addressed their specific systems in the same way to develop an adequate initial maintenance program.
Armed with information on system operation, maintenance significant items MSIs and their associated functions, failure modes, failure effects, and failure causes, the group analyzed each item using a logic tree to determine requirements. This approach to maintenance program development was called a bottom-up approach because it looked at the components as the most likely causes of equip- ment malfunction. The purpose of the analysis was to determine which of three processes would be required to repair the item and return it to service.
This maintenance steering group MSG approach to maintenance program development was so successful on the that it was modified slightly for use with other aircraft. The specific references to the airplane were removed, and the new generalized process could be used on all aircraft. Other slight modifications were made to the process in by European manufacturers, and the resulting procedure used in Europe became known as EMSG.
The MSG-2 process was slightly different for the three maintenance areas studied: Table summarizes the steps for each: Development of Maintenance Programs Step 1, identify the maintenance or structure items requiring analysis. Step 2, identify the functions and failure modes associated with the item and the effect of a failure. Step 3, identify those tasks which may have potential effectiveness. Step 4, assess the applicability of those tasks and select those deemed nec- essary.
Step 5, for structures only, evaluate initial sampling thresholds. The process flow diagram in the MSG-2 document is too complex to repeat here, especially since the MSG-2 process is no longer used.
It is important, however, to understand how the maintenance processes were assigned to the tasks selected. Figure is a simplified diagram of that process. Briefly, if failure of the unit is safety related block 1 and there is a maintenance check available to detect a reduction in failure resistance block 4 , then the item in question is iden- tified as on-condition.
If no such check is available, then the item is classified as hard time. The student can follow the logic of Fig. Once the maintenance action was determined, it was necessary to define how often such maintenance should be done. Available data on failure rates, removal rates, etc. Process-Oriented Maintenance Process-oriented maintenance programs are developed for aviation using deci- sion logic procedures developed by the Air Transport Association of America ATA.
The MSG-2 process is a bottom-up approach whereby each unit system, component, or appliance on the aircraft is analyzed and assigned to one of the primary maintenance processes, HT, OC, or CM. In general, hard time means the removal of an item at a predetermined inter- val, usually specified in either so many flight hours or so many flight cycles. In some cases the hard time interval may be in calendar time.
On-condition means that the item will be checked at specified intervals in hours, cycles, or calen- dar time to determine its remaining serviceability. Condition monitoring involves the monitoring of failure rates, removal rates, etc. Let us look at each process in more detail.
The hard time interval may be specified by calendar time, by engine or airplane check interval engine change, C check, etc. When HT is specified, the component will be removed from the vehicle and overhauled, restored, or discarded, whichever is appropriate. This will be done before the component has exceeded the specified time interval.
The component overhaul or restoration will restore the component to a condition that will give reasonable assurance of satisfactory operation until the next scheduled removal.
Ideally, hard time would be applied to a component that always fails at X hours of operation. This component would then be replaced at the last scheduled main- tenance period prior to the accumulation of X hours; thus, the operator would get maximum hours out of the component and the component would never fail in service ideally. Hard time is also applied to items having a direct adverse effect on safety and items subject to reliability degradation with age but having no possible mainte- nance check for that condition.
The former components, as we will see later, are not eligible for condition monitoring because of the safety issue. The latter com- ponents, such as rubber products, do not lend themselves to any periodic check for condition; i.
As an example, structural inspection, landing gear overhaul, and replacement of life-limited engine parts are all controlled by hard time. Frequently, mechan- ical linkages and actuators, hydraulic pumps and motors, electric motors and gen- erators, and similar items subject to a definite wear-out cycle will also be identified as hard time.
For items having clearly defined wear-out periods, hard time is probably the most economical process. However, these items can also be OC or CM, depending on the operator, as long as they are not safety related. The on-condition OC process On-condition is a failure preventive process that requires that the item be peri- odically inspected or tested against some appropriate physical standard wear or deterioration limits to determine whether or not the item can continue in service.
After failing an OC check, the component must be overhauled or restored to the extent of at least replacing out-of-tolerance parts. Overhaul or repair must restore the unit to a condition that will give reasonable assurance of sat- isfactory operation for at least one additional OC check interval. If the item cannot be overhauled or restored, or if it cannot be restored to a condition where it can operate one more OC check period, then it should be discarded.
On-condition must be restricted to components, equipment, or systems on which a determination of continued airworthiness may be made by measure- ments, tests, or other means without doing a tear-down inspection. These on- condition checks are to be performed within the time limits intervals prescribed for each OC check. The periodically scheduled OC checks must constitute meaningful determi- nation of suitability for continued operation for another scheduled OC check interval.
If the check performed provides enough information regarding the condition and failure resistance of the item to give reasonable assurance of its continued airworthiness during the next check period, the item is properly cat- egorized as on-condition. It should be classified as CM and not OC.
In some cases, it could even be classified as HT. A simple operational check is not an accept- able requisite for the on-condition process. The on-condition process also encompasses periodic collection of data that will reveal the physical condition of a component, system, or engine. On-condition data must be directed to an individual component, system, or engine by serial number. Examples of OC checks are as follows: In each of the above stated cases, one can measure degradation and determine, from established norms, how much life or serviceability remains.
Most of the commercial airplane operators in the United States use the on- condition process to control engine overhaul. The determination of when to remove an engine is based on engine data collected by an ECM program. Data showing engine performance degradation, such as oil and fuel consumption, borescope inspection results, trends in recorded in-flight instrument readings, oil analysis, etc.
Engine data programs attempt to provide data to indicate the need to remove engines before an in-flight shutdown IFSD occurs; i. Two points to remember about the on-condition process: Examples of components susceptible to the on-condition process are as follows:. Brake wear indicator pins: Compare brake wear condition against a specified standard or limit.
Control cables: Measure these for diameter, tension, and broken strands. Linkages, control rods, pulleys, rollers tracks, jack screws, etc.: Measure these for wear, end or side play, or backlash. The condition monitoring CM process The condition monitoring process is applied when neither the hard time nor the on-condition process can be applied.
The CM process involves the monitoring of the failure rates, removals, etc. Condition monitoring is not a failure preventive process as are HT and OC. There are no maintenance tasks suitable for evaluating the life expectancy of the CM item and there is no requirement to replace the item before it fails.
Neither time nor condition stan- dards can be used to control CM items because these components do not have such attributes. Therefore, CM components are operated until failure occurs and replacement of CM items is an unscheduled maintenance action. Since CM items are operated to failure, the ATA states that these items must 1 comply with the following conditions:. A CM item has no direct, adverse effect on safety when it fails; i.
Generally, CM items have only this indirect, nonadverse effect on safety due to system redundancy. A CM item must not have any hidden function i. However, if there is a hidden function and the availability or operation of that hidden function is verified by a scheduled operational test or other nonmea- surement test made by the flight crew or maintenance crew, CM can still be used.
A CM item must be included in the operators condition monitoring or relia- bility program; i. In addition to the above ATA stipulations, CM items usually have no adverse relationship between age and reliability i. They exhibit a random failure pattern. The most appropriate application of the condition monitoring process is to com- plex systems, such as avionics and electronics components, and to any other com- ponents or systems for which there is no way to predict failures.
Typical components and systems suitable for CM include navigation and communications equipment, lights, instruments, and other items where test or replacement will not predict.
This document is no longer kept up to date by ATA. In aviation, CM is fre- quently applied to components where failure has no serious effect on safety or air- worthiness, due to redundancy, and to items not affecting airworthiness at all, such as coffee makers, lavatories, passenger entertainment systems, etc.
Condition monitoring systems consist of data collection and data analysis procedures that will portray information upon which judgments relative to the safe condition of the vehicle can be made.
A CM program includes those kinds of evaluation programs that utilize the disclosure capabilities of the airplane or its systems and components to the degree that such disclosure information can be used to make judgments relative to the continuing safe condition of the air- plane, its systems, engines, and components. Evaluation based on reports by flight crews, on-board data systems, and equipment for ground check of system performance may be used for CM actions. The basic elements of a CM program may include data on unscheduled removals, maintenance log entries, pilot reports, sampling inspections, mechanical reliability reports, shop findings, and other sources of maintenance data.
These and other data may indicate a problem area and thus the need to investigate the matter see Chap. Condition monitoring, which is primarily a data collection and analysis pro- gram, can also be used on HT and OC components for verifying or adjusting the HT and OC intervals. For example, if a hard time item is removed just prior to its expiration date and overhaul activities reveal that little or nothing needs to be done to restore the component, then perhaps the HT interval can be extended.
Likewise, if OC checks reveal little or no maintenance requirement or that the lifetime of the component is longer than originally expected, the OC check inter- val can be changed. However, without the collection of data over a period of time several HT periods or OC intervals , there would not be any solid justification to change the intervals.
By the same token, CM data collection may indicate that the HT or OC intervals need to be shortened for some components. The CM pro- gram also provides data to indicate whether or not components are being mon- itored under the most appropriate process.
Note for the technical purists Condition monitoring does not really monitor the condition of a component. It essentially monitors the failure or removal statistics of the unit. You moni- tor the components condition with the on-condition process. Task-Oriented Maintenance Task-oriented maintenance programs are created for aviation using decision logic procedures developed by the Air Transport Association of America.
The MSG-3 technique is a top-down consequence of failure approach whereby failure analysis is conducted at the highest management level of air- plane systems instead of the component level as in MSG There are three cat- egories of tasks developed by the MSG-3 approach:.
Airframe system tasks 2. Structural item tasks 3. Zonal tasks. Maintenance tasks for airframe systems Under the MSG-3 approach, eight maintenance tasks have been defined for airframe systems. These tasks are assigned in accordance with the decision analysis results and the specific requirements of the system, component, etc.
These eight tasks are listed and defined below:.
An examination of an item and comparison against a specific standard. Functional check. A quantitative check to determine if each function of an item performs within specified limits. This check may require use of additional equipment. Operational check. A task to determine if an item is fulfilling its intended pur- pose. This is a failure-finding task and does not require quantitative toler- ances or any equipment other than the item itself. Visual check. An observation to determine if an item is fulfilling its intended pur- pose.
This is a failure-finding task and does not require quantitative tolerances. That work necessary to return the item to a specific standard. Restoration may vary from cleaning the unit or replacing a single part up to and including a complete overhaul.
The removal from service of any item at a specified life limit. Maintenance tasks for structural items Airplanes are subjected to three sources of structural deterioration as discussed below. Environmental deterioration. The physical deterioration of an items strength or resistance to failure as a result of chemical interaction with its climate or environment. Environmental deteriorations may be time dependent.
Accidental damage. The physical deterioration of an item caused by contact or impact with an object or influence that is not a part of the airplane, or damage as a result of human error that occurred during manufacture, oper- ation of the vehicle, or performance of maintenance. Fatigue damage. The initiation of a crack or cracks due to cyclic loading and subsequent propagation of such cracks. Inspection of airplane structures to determine if deterioration due to the above has occurred requires varying degrees of detail.
The MSG-3 process defines three types of structural inspection techniques as follows:. General visual inspection. A visual examination that will detect obvious, unsatisfactory conditions or discrepancies. This type of inspection may require removal of fillets or opening or removal of access doors or panels. Work stands and ladders may be required to facilitate access to some components. Detailed inspection. An intensive visual inspection of a specified detail, assembly, or installation.
It is a search for evidence of irregularity using adequate lighting and, where necessary, inspection aids, such as mirrors, hand lenses, etc. Surface cleaning and detailed access procedures may also be required. Special detailed inspection. An intensive examination of a specific location. It is similar to the detailed inspection but with the addition of special tech- niques.
This examination may require such techniques as nondestructive inspections NDIs: The special detailed inspection may also require the disassembly of some units. Zonal maintenance tasks2 The zonal maintenance program ensures that all systems, wiring, mechanical controls, components, and the installation contained within the specified zone on the aircraft receive adequate surveillance to determine the security of instal- lation and general condition. The logical process is normally used by type cer- tificate TC and supplement type certificate STC holder for developing their maintenance and inspection for zonal maintenance by using MSG-3 logic to develop a series of inspections, and a numerical reference is assigned to each zone when it is analyzed.
Due to aging aircraft, the FAA has established spe- cific damage tolerance criteria based on inspection of an aircraft operators con- tinued airworthiness program. The AC provides for detailed damage tolerance inspection DTI for repair and alterations that affect fatigue-critical.
AC A. This program was initiated after the TWA flight crash. The DTI process includes the area to be inspected, the inspection methods and techniques, and the inspection procedures. The program packages a number for general visual inspection tasks, gener- ated against the item in the systems maintenance program, into one or more zonal surveillance tasks.
Zonal maintenance and inspection level techniques are performed in two types as in the following list. General visual inspection 2. Detailed visual inspection. The MSG-3 program adjusted the decision logic to provide a more straight- forward and linear progression through the logic.
The MSG-3 process is a top- down approach or consequence of failure approach. In other words, how does the failure affect the operation? It does not matter whether a system, subsystem, or component fails or deteriorates. What matters is how the failure affects the aircraft operation.
The failure is assigned one of two basic categories: Figure is a simplified diagram of the first step in the MSG-3 logic process. The MSG-3 approach is more flexible in developing the overall maintenance program. The flow chart of Fig. Those failures that are evident are further separated into safety related and operationally related with the latter split into those that are of economic significance and those that are not. These types are numbered 5, 6, and 7.
The significance of these categories will be addressed later. Those failures that are determined to be hidden from the crew are divided into safety related and nonsafety related items. These are designated as cate- gories 8 and 9. Revised several times March ; September , March ; and March The latest changes were in revision The The latest revision The numbers on the output block 5 through 9 are used later to identify the category of the failure hidden, evident, safety, etc.
These numbers will be referenced later in this discussion. Figure MSG-3level I analysisfailure categories. Reprinted with permission. Figures and level II analysis are used to determine the maintenance tasks required to accommodate the functional failure. Although the questions are similar, there is a slight difference in the way evident and hidden failures are addressed.
Note that some of the flow lines in Figs. This requires some explanation. The first question in each chart, regarding lubrication or servicing, must be asked for all functional failures categories 5 through 9. Regardless of the answer to this question Yes or No , the analyst must ask the next question.
For categories 6 and 7 in Fig. At that point the analysis stops. For categories 5 and 8 safety related , however, all questions must be answered regardless of the Yes or No response to any of them. The last block of Figs. These flow charts are used for the development of a maintenance program for a new air- craft or derivative.
However, if the item is safety related categories 5 or 8then a redesign is mandatory. Once the initial maintenance program is developed, the airline mechanics will use that program. Mechanics do not have the option of redesign unless that is indicated by the reliability pro- gram as discussed in Chap.
The MSG-3 process can be best understood through a step-by-step explana- tion of what the working groups would do for a given analysis. Each working group will receive information about the systems and components within their respective groups: If the equipment is new, or has been extensively modified for the new model aircraft, the learning process may take a little more time. The airframe manufacturer is responsible for providing this training to the work- ing groups.
The manufacturer is also responsible for furnishing any available performance and failure rate data to the working groups. Once the group assimilates this information, they begin to run through the logic diagrams, answering the questions appropriately and determining the maintenance approach that best suits the problem. Each failure in each oper- ational mode is addressed. The working group first determines if the failure is hidden to the crew or is obvious block 1 of Fig.
Then they determine whether or not the problem is safety related and, in the case of evident failures, whether or not it has operational impact.Therefore, the goals of an airline maintenance program can be stated as follows:. In Chap. The physical limit of the components materials has been reached. Specifically, he represented Boeing to airlines on the ETOPS extended-range twin-engine operations program, participated in airline maintenance evaluations, and helped airlines develop reliability programs.
Quality Control Today, years after the Wright Brothers historic first flight, aviation has come of age.
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