AMM_Chapter 1 (Introduction-2013)

7/27/2019 AMM_Chapter 1 (Introduction-2013)

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Chapter 1:

Prepared by : Nur Rachmat, Dipl. Ing., M.Sc.

Ref. Used : Aviation Maintenance Management,Harry A. Kinnison & Others.


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Chapter 1:

Introduction

Prepared by : Nur Rachmat, Dipl. Ing., M.Sc.

Ref. Used : Aviation Maintenance Management,

Harry A. Kinnison & Others.


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Definitions, Goals & Objectives.


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Definitions, Goals & Objectives.

This section discusses some basic terms used in

aviation maintenance and engineering and some wordpairs used in aviation that are, in conventional usage,

synonymous, but in the world of science and engineering

and especially aviation they take on subtle differences. It

begins with the most important definition which is

maintenance.


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Definitions of MaintenanceLindley R. Higgins, defining maintenance as art, science,

and philosophy. In this course, however, we will address the

subject in less poetic and more practical terms.

Numerous other authors have defined the term maintenancebut their definitions are somewhat unsatisfactory.

Most of them are not incorrect but they are often inadequate

to describe the full scope and intent of the maintenance effort.

A few of these will be discuss the differences.


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Typical airline definition of maintenance This one was taken from the text of a "typical" airline's

technical policies and procedures manual (TPPM).

Maintenance is defined as "those actions required fix restoring

or maintaining an item in a serviceable condition, includingservicing, repair, modification, overhaul, inspection, and

determination of condition."

This is not incorrect. However, it merely describes what

maintenance people do; it is not descriptive of the intent, or theresult of maintenance activity.


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Moubray's definition of maintenance

John Moubray, an industrial consultant in the United

Kingdom, took the RCM philosophy and applied it to the

maintenance of machines and equipment in a typicalmanufacturing plant.

He presented the following definition of maintenance in his

book on the subject t Maintenance is "... ensuring that physics

assets continue to do what their users want them to do."


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Hessburg's definition of maintenance

Jack Hessburg, former chief mechanic for the Boeing 777

design effort, has provided a definition of maintenance which

gives a broader view of' the field. "Maintenance is the action

necessary to sustain or restore the integrity and performance

of the airplane" t He goes on to say that maintenance

"includes inspection, overhaul, repair, preservation, andreplacement efforts." This definition is more accurate.


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Kinnison's definition of maintenance

The author of this textbook feels that the abovedefinitions-although well intended and, in most cases,

adequate in general terms are not fully descriptive ofwhat the maintenance process is about. The definitionin the box below will be used in this course.

Maintenance is the process of ensuring that a system

continually performs its intended function at its designed-inlevel of reliability and safety.


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Regulation definition of maintenance

In the Federal Aviation Regulations, FAR part 1, maintenance is

defined as "inspection, overhaul, repair, preservation, and

replacement of parts. "t Again, this describes what maintenance

people do but it is not a definitive description of what maintenance

is intended to accomplish.

According to CASR Part 1 "Maintenance" means inspection,

overhaul, repair, preservation, and the replacement of parts, but ex-cludes preventive maintenance.


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Definitions ofInherent Reliability

Inherent reliability is a term used frequently in aviation. This

term may require some clarification. Nowlan and Heap state

that "the inherent reliability of an item is not the length of

time it will survive with no failures; rather, it is the level of

reliability the item will exhibit when it is protected by

preventive maintenance and adequate servicing andlubrication."

The authors go on to say that the degree of reliability achieve,

depends upon design characteristics of the equipment and the

process used for determining the maintenance requirements(i.e., the MSG process). In other words, the inherent

reliability of a system or component is both a function ') the

design and a function of the maintenance program

established for it. The two are interrelated.


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Definitions ofMechanics, Technicians,

Maintainers, Engineers

The terminology used by the world's airlines to identify

maintenance personnel varies. The terms mechanic,technician, and maintainerare often used to identify thosewho per form the scheduled and unscheduled maintenance

task of the uni t' s aircraf t. In some organizations, however,these same people all called engineerswhile in others, theterm engineer is reserved for those personnel who havecollege degrees in one of the engineering fields. These peopleusually perform duties quite different from those of the line,hangar, and shop maintenance people.In this course, for the sake of standardization of thediscussion, It defines those who work on the scheduled andunscheduled aircraft maintenance task (line, hangar, or shop)as mechanics, technicians, ormaintainers, while those whowork in the technical services organization as specified in

Chap. 2 will be calledengineers.


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Word Pairs Used in Aviation

There are a number of word pairs that we use in aviation

that are assigned very specific meanings. These meanings are

more precise than those addressed in the dictionary. Among

them are; Verification and validation, Operational and

functional, Goals and objectives, there may be more.

These words are used in aviation, as well as in the railroadindustry, in relation to determining the adequacy of maintenance

processes and procedures. Although some dictionaries define

one of these words with the other one, in the world of

engineering and technology there are various definitions givendepending on the application.


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IntroductionWord Pairs Used in Aviation

Verification and validation

In aviation, it is generally accepted that the two words have

distinctly different meanings. Many procedures are written to

test or measure the condition, accuracy, or availability of

equipment and systems. The words verification and validation

describe different approaches or concepts used to assure that

maintenance has been properly addressed by such procedures.


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Verification and validation

Verificationmeans that a test or procedure has been writtenand that, when read and understood by a knowledgeable person,

is deemed to be correct, adequate, and acceptable for the purpose

for which it was intended.

Validation, on the other hand, means that the written test orprocedure has been performed by an appropriately trained

maintenance person, and the procedure, as written, is

understandable, adequate, and, most importantly, proven to

accomplish the intended purpose.


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Verification &Validation

In other words, verification means that the procedure exists and is

acceptable based on the knowledge and understanding of the related

equipment and on perusal of the procedure itself.

Validation means that the procedure has actually been performed as

written and has been deemed to be adequate and acceptable.


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Operational check means to operate the equipment,

system, or component as usual (all modes and functions)and determine whether or not it is useable for its intendedpurpose. No special test equipment or tools are needed andno measurements are taken. An operational check is definedas "a task to determine if an item is fulfilling its intended

purpose. This is a failure finding task and does not requirequantitative tolerances."

Functional check means that the equipment, system, orcomponent has been checked out using the necessaryequipment and tools to measure certain parameters for

accuracy (i.e., voltages, frequencies, physical measures suchas gap size, length, weight, etc.). The official definition for afunctional check is "a quantitative check to determine ifeach function of an item performs within specified limits."*The term "limits" here implies a check or measurementagainst some standard.


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Goals and objectives

There seems to be considerable confusion throughout the

engineering profession and perhaps other fields as well, about

the similarities and differences between "goals" and

"objectives."

Some modern dictionaries, as they have done with many pairs

of similar words, define one word with the other one makingthe two nearly synonymous. But these two words goals and

objectives have always had specific meanings to this author

and to many other people in the technic fields.

We have taken the liberty of writing our own definitions forthese tern in order to establish a clear understanding and

application of the two words for use throughout this book.


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Goals and objectivesA goalis a point in time or space where you want to be; a

level of accomplishment you want to achieve.

An objectiveis the action or activity you employ in order

to help you achieve a specific goal.

In other words, a goal is where you want to be; an

objective is how you plan to get there.


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Goals and objectivesExample: Suppose a person living in Seattle, Washingtonwants to be in Dallas, Texas for Christmas with family

members. First, the mode of travel must be determined (private

auto, bus, train, or airplane) and then, depending on which

mode is chosen the desired dates of departure and return must

be determined. Of course there are numerous decisions that

must be made and eachpossible choice will have its own pros

and cons. This must be worked out ahead of time. In this

simple example, being in Dallas for Christmas is the goal. Theobjective is to make the trip happen and that involved the

planning and decision making activities, which would vary with

the mode choice that would be necessary to make the trip

possible.


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Goals and Objectives of Maintenance


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Introduction

We will established the fact in the next sub-chapter

(Reliability), that we cannot make perfect systems and that thesystems we have will fail at various times and for a variety of

reasons.

We will also established, in the same sub-chapter, various

management actions to minimize the effects of serviceinterruptions caused by these failures (LRUs, redundancy,

minimum dispatch requirements).

Also, the manufacturer has established a maintenance

program that includes numerous tasks at scheduled intervals aswell as references to other tasks and maintenance manual

procedures for addressing the unscheduled failures. But these

are not quite enough.


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Goals and Objectives of Maintenance

To establish an effective airline maintenance program that

will effectively implement these tasks, achieve the reliabilityand safety standards we desire, and still maintain an adequate

flight, schedule to stay in business, we must have some

additional guidelines. Namely, we need to establish some goals

and objectives for an airline maintenance program.


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Goals of a maintenance program

The purpose of any transportation company is to move

people and/or goods from one place to another, usually for aprofit. This means, to some people, that the operational part of

the unit is more important than the maintenance part.

The two are actually on a par as far as management and

administration are concerned. But, the fact remains that themaintenance organization is in business to support the unit's

operation.

Maintenance must ensure that the flight department has

vehicles available to carry out the flight schedule, and this

schedule should be met with all required maintenance

completed. Therefore, the goals of an airline maintenance

program can he stated as follows:


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1. To deliver airworthy vehicles to the flight department in time

to meet the flight schedule2. To deliver these vehicles with all necessary maintenance

actions completed or properly deferred

The FAA requires maintenance to be done at specified

intervals and to accepted standards. The FAA also requires thatthis work be done at or before the appointed time.

If there are circumstances that prevent work being done (lack

of parts or qualified maintenance personnel, time constraints,

etc.) the FAA allows such maintenance to be deferred to a

more opportune time.


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Deferrals of certain items can be in accordance with the MEL

others can be deferred through the short-term time escalationprogram identified in the FAA approved maintenance program.

The accepted standards include the manufacturer's, the

regulator's, and the operator's standards of safety and

reliability. The time limits refer to the maximum number of hours or

cycles of operation and any calendar limits (days, months, etc.)

as prescribed by the approved maintenance program. The

repair must be completed within the specified deferral time

and this cannot be extended.


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Maintenance program objectives

To achieve the stated goals of a maintenance program, we need to

identify the objectives we will employ.

The Air Transport Association of America (ATA) has identified four

objectives of a maintenance program. The FAA, the airframe

manufacturers, and the airlines repeat these objectives throughout

their own literature. These objectives were developed in conjunctionwith the established merit of the initial maintenance program when a

new airplane model was being developed (i.e., the MSG-3 process).


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These objectives are not quite sufficient for a good, effective

maintenance program at the operator's level once the equipment

enters service.

For this in service activity, five objectives of a maintenance

program are established and addressed in this textbook. The list below

contains the ATA objectives, from the aforementioned document,with the addition of one very important objective - objective number

three in this new list.


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ATA Maintenance program objectives

The objectives of an airline in service maintenance program are as

follows:

1. To ensure the realization of the inherent safety and reliability levels of theequipment

2. To restore safety and reliability to their inherent levels when deterioration has

occurred

3. To obtain the information necessary for adjustment and optimization of the

maintenance program when these inherent levels are not met

4. To obtain the information necessary for design improvement of those items

whose inherent reliability proves inadequate

5. To accomplish these objectives at a minimum total cost. including the costs of

maintenance and the cost of residual failures


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Experience may show an operator that maintenance intervals

established by the manufacturer may not be the best for that

airline's operational environment. The results of maintenance

may also be less than expected because of bad parts, improper

or inadequate procedures, or even the lack of proper training of

the mechanics. All of these could affect the overall reliabilityand. safety of the equipment and they should be addressed by

the airline before calling the manufacturer and requesting or

demanding a redesign of that equipment as implied by objective

4. This is the reason for the added objective.


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Contrary to popular belief, the manufacturers cannot be

blamed for all the problems occurring with the equipment

once it is in the field. Therefore, the airline must look into its

own operation first. Keep in mind, however, that any serious

problems in any of the areas above relating to the airline's

ability to meet its objectives could affect the operator's FAAcertification. So these conditions should always be monitored

closely and corrected if found to be lacking.


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Maintenance Program Content

The ATA document cited above discusses what a

maintenance program should be as stated below.

The maintenance program consists of two groups of tasks:

a group of scheduled tasks to be accomplished at specified

intervals and

a group of non-scheduled tasks which result from

(a) conducting the scheduled tasks,

(b) from reports of malfunctions, and

(c) from data analysis.


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Discussion of the ATA Five Objectives

Objective 1: To ensure the realization of the inherent, safety andreliability levels of the equipment. This objective is satisfied by a series

of scheduled maintenance tasks. The scheduled maintenance tasks may

be developed by the manufacturer, Curer of the equipment, by the

maintenance organization of the airline, a third party maintenance

company, by some industry-supported organization (trade association),or by some combination of these. Usually; the manufacturer supplies the

operator with basic information on how the equipment works and some

basic troubleshooting techniques, as well as servicing,

removal/installation procedures, and maintenance procedures.


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Objective 2: To restore safety and reliability to their inherent

levels when deterioration has occurred. This objective is satisfied by

unscheduled maintenance tasks developed by the MSG process and

contained in the manufacturer's maintenance manual.

Unscheduled maintenance tasks result from a combination of

activities: (a) troubleshooting actions that determine the nature andcause of the problem; (b) removal and replacement of parts or

components to effect repair or restoration; and (c) performance of

certain tests and adjustments to ensue proper operation of the system

or equipment after the "fix" has been implemented.


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Objective 2: Unscheduled maintenance tasks, developed by the

manufacturer, and sometimes modified, in the field, by the operators

through experience. Such modifications, however, must be approved by

the FAA.

Reports of malfunctions come from operators and users through

various means, usually a logbook kept in the airplane or by verbal orwritten report from operators, flight crews, cabin crews, users, or

maintenance personnel. Maintenance tasks that result from data analysis

are usually actions that result from some form of reliability program or

other failure rate analysis activities conducted by quality control (QC).


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Objective 5. In other words, a good maintenance program, to beeffective, must provide airworthy vehicles to the operations

department at a reasonable cost.

As an example, suppose a component or system is checked daily,

in accordance with the scheduled maintenance program, and a

problem is found may be every 2 or 3 weeks (or even less often). It issensible, then, to reschedule this check to perhaps a weekly or even a

biweekly interval to reduce maintenance costs.

. When it comes to maintenance, more is better but only up to a

point.


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Reason for Maintenance


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The aim of doing maintenance is to keep the performance and the

reliability of the aircraft within design limits so that it can still do the jobit was bought to do. Two kinds of processes affect an aircraft, which are:

deterioration with age, chance failures. So maintenance can be

considered under three sub headings: Precautionary work to ensure that there has been no undetected

chance failures. Inspection to monitor the progress of wear out processes. Preventive work to anticipate and prevent failures.

If preventive work is to be worthwhile two conditions must be met:

The item must be more reliable after the maintenance action than itwas before. The cost of the maintenance action must be less than the failure it is

intended to prevent.


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Thermodynamics Revisited

There is one concept in thermodynamics that is often a puzzler

to 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 system,

any system. When they finished, they had anequation of morethan several terms; and all but one of these terms were easily

explainable. They identified the terms for heat energy, potential

energy, kinetic energy, etc., but one term remained. They were

puzzled about the meaning of this term. They knew they haddone the work correctly; the term had to represent energy.


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Thermodynamics Revisited

The late Dr. Isaac Asimov, biophysicist and prolific writer of

science fact at science fiction, had the unique ability to explain

the most difficult science the layman in simple, understandable

terms. Dr. Asimov says that if you want to understand the

concept of entropy in practical terms, think of it as the deference

between the theoretically perfect systems you have on thedrawing 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 canbuild, constitutes the natural entropy of the system.


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A Saw Blade Has Width

This concept of entropy, or unavailable energy, can be

illustrated by a similar example, mathematically, it is possible to

take a half of a number repeatedly forever. That is, half of one is

1/2; half of that is 1/4, half of that is 1/8 and so to infinity.

Although the resulting number is smaller and smaller each time

you divide, you can continue the process as long as you canstand to do so, you will never reach the end.

Now, take a piece of wood about 2 feet long (a 2 x 4 will do)

and a crosscut section. Cut the board in half on the short

dimension). Then take one of the pieces cut that in half. You cancontinue this until you reach a point where you can longer hold

the board to saw it.


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The Role of the Engineer & Mechanic

The design of systems or components is not only limited by the

imperfection, the physical world (i.e., the "natural entropy" of the

system), it is also limited a number of other constraints which we

could refer to as "man-made entropy."

A design engineer may be limited frommaking the perfectdesign

by the technology or the state of the art within any facet of thedesign effort.

He or she may be limited by ability or technique; or, more often

than not, the designer may be limited by economics; that is, there

just is not enough money to build that nearly perfect system that is

on thedrawing board or in the designer's mind.


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The Role of the Engineer & Mechanic

Although the designer is limited by many factors, in the tradition

of good engineering practice, the designer is obliged to build the

best system possible within the constraints 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 responsible for budget asks, "How much will it cost tobuild this`'" The designer has meticulously calculated that these

widgets can be mass produced for $1200 each, "Great," says the

boss. "Now redesign it so we can build it for under a thousand

dollars."


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The Role of the Mechanic

To summarize, then, it is the engineer's responsibility to design

the system with as high a degree of perfection (low entropy) as

possible within reasonable limits. The mechanic's responsibility, on

the other hand, is to combat the continual increase in entropy

during the operational lifetime of the equipment.


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Two Types of Maintenance

Figure 1-2 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. Notethat the curvebegins to turn downward with time. This is a

representation of the natural increase in entropy of the system, the

natural deterioration of the system over time. When the system

deteriorates to some lower (arbitrarily set level of perfection, weperform some corrective action: adjusting, tweaking, servicing, or


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Two Types of Maintenance

Figure 1-3 shows the system restored to its normal level (curves a

and b). There are times, of course, when the system deterioratesrather rapidly in service 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, troubleshooting,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 problem are referred to as unscheduled maintenance.


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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 ofperfection 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 be performed to increase the system

reliability any higher than this inherent level. However, it isdesirable 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 Chap. 5, but there is one more

important point to cover here; that is redesign of the equipment.


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Introduction


RedesignFigure 1-4 shows the original curve of our theoretical system,

curve A. The dashed line shows the system's 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-made entropy may result because the designerapplied tighter tolerances attained improved design skills, orchanged the design philosophy.


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Redesign

The question to be considered, then, is this: Does the reduction of

maintenance justify the cost of the redesign? This question, ofcourse, is a matter for the designers to ponder, not the maintenance

people,One of the major factors in redesign is cost. Figure 1-5 shows the

graphs of two familiar and opposing relationships. The upper curveis logarithmic. It represents the increasing perfection attained with

more sophisticated design efforts. The closer we get to perfection

(top of the illustration) the harder it is to make a substantial

increase. (We will never get to 100 percent.) The lower curvedepicts the cost of those ongoing efforts to improve the system.


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Failure Rate Patterns

TABLE 1-1 Failure Rate Patterns


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Master Minimum Equipment List Line

(MMEL/MEL)


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(MMEL/MEL)

The items are identified in the MMEL by flight crew personnel during

the latter stages of new aircraft development. Thus, flight personneldetermine 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 thetime 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 airline's MEL. Maintenance must abide by

that decision.


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Technical Management


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The handbook is written for those who have background and

experience in aviation maintenance and who wish to move intolower and middle level management positions within the airline's

maintenance and engineering section. Those managers without a

technical background, of course, can still benefit from the

handbook by expanding their horizons to the technical realm.Mechanics and technicians who desire to move into the

management of maintenance will gain valuable information about

the overall operation of the maintenance and engineering unit.

Aviation Industry Interaction


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Aviation Industry Interaction

The aviation industry is unlike any other transportation mode.

In aviation, we cannot pull off the road and wait for a tow truckwhenever we a have problem. We are required by the

regulations to meet all maintenance requirements before

releasing a vehicle into service. This is often not the case with

other commercial transport modes. In aviation we have arelationship with gravity that differs considerably from that of

any other transportation mode. We have problems with extremes

of temperature (e.g., very hot engines and very cold air at high

altitude).


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Summary


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Summary

This chapter has addressed various terms relating to the

maintenance effort which will be used or referencedthroughout the remainder of the presentation. The use and

understanding of these terms and definitions should

become second nature to the audience/reader.

Documents

AMM_Chapter 1 (Introduction-2013)