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This means not only that a real system which starts off being new will have some ... These are 'operate to failure' items in categories D, E and F : ... – PowerPoint PPT presentation

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Title: 393SYS

1.0 Why We Have to Do Maintenance
The Role of the Engineer
  • Perfect systems can be designed on paper but
    perfect systems cannot be built in the real
  • A design engineer may be limited from making the
    perfect design by
  • imperfections in the natural world
  • technology
  • ability
  • economics
  • Very often there is just not enough money to
    build a (nearly) perfect system.

1.0 Why We Have to Do Maintenance
  • However, the designer is obliged to build the
    best system possible within the constraints
    which exist.
  • A project manager for a new aircraft will be
    responsible for the project budget.
  • He will ask his design manager, how much will
    it cost to build this ?
  • The design manager might say 120M.
  • The project manager, however, might be limited
    to a budget of 100M for the production cost of
    each of the new aircraft.
  • In this case, the design manager must redesign
    the new aeroplane so it can be built for 100M.

1.0 Why We Have to Do Maintenance
  • That usually means reduced tolerances, cheaper
    materials, and, consequently, more entropy.
  • More entropy in the design will mean more
    maintenance is required.
  • The design engineers main problem is then to
    minimize (not eliminate) the entropy of the
    system he or she is designing while staying
    within the required constraints.

1.0 Why We Have to Do Maintenance
The Role of the Mechanic
  • Entropy exists in every system and the entropy
    of a system is always increasing.
  • This means not only that a real system which
    starts off being new will have some entropy
    already built into it, but that the entropy will
    increase with time.
  • Some components or systems will deteriorate from
    use, or even lack of use.
  • Misuse by an operator may cause some
  • Therefore, while the engineers job is to
    minimize the entropy of a system during design,
    the mechanics job is to fight the continual
    increase in the entropy of a system during its

1.0 Why We Have to Do Maintenance
This graph shows the level of perfection of a
typical system
100 perfection is at the very top of the
y-axis. The x-axis shows time. The solid curve
shows the level of perfection of a real world
system. Note that the curve turns downwards with
1.0 Why We Have to Do Maintenance
When the system deteriorates to some lower level
of perfection, it is necessary to perform some
corrective action - adjusting, servicing, etc.
System needs to be corrected when it reaches some
lower level.
1.0 Why We Have to Do Maintenance
  • In other words, at some point, we have to
    perform some maintenance to restore the system
    to its designed-in level of perfection.
  • We need to reduce the entropy to its original
  • This is called preventative maintenance and is
    usually performed at regular intervals.
  • This is done to prevent deterioration of the
    system to an unusable level.
  • Preventative maintenance is also sometimes
    referred to as s scheduled maintenance.
  • This schedule could be daily, every flight,
    every 200 flight hours, or every 100 cycles ( a
    cycle is a takeoff and landing).

1.0 Why We Have to Do Maintenance
  • Considering the number of components on a modern
    aircraft, maintenance is a complex, on-going
  • For this reason, we will see that aircraft
    maintenance must be approached systematically.
  • Definition
  • systematic
  • adjective done using a fixed and organized plan
    e.g. the systematic collection and analysis of
    informationsystematically adverb

1.0 Why We Have to Do Maintenance
  • Failure Rate Patterns
  • Not all systems or components fail at the same
    rate nor do they all exhibit the same pattern of
    wear out and failure.
  • This is important because the nature of the
    maintenance to be performed on these systems and
    components is related to their failure rates and
    failure patterns.
  • United Airlines did some studies on lifetime
    failure rates and found six basic patterns.
  • These are shown in the following table.
  • Note
  • The vertical axes show failure rates, not
    reliability ! The higher the vertical position,
    the worse the failure rate.
  • The horizontal axes show time.

1.0 Why We Have to Do Maintenance
A. Infant mortality constant or slightly rising
failure rate definite wear out period (4 ).
B. No infant mortality slightly rising failure
rate definite wear out period (2 ).
C. No infant mortality slightly rising failure
rate no definite wear out period (5 ).
D. Increasing failure rate at outset constant or
slightly rising failure rate no definite wear
out period (7 ).
E. No infant mortality constant failure rate
throughout life no definite wear out period (14
F. Infant mortality constant failure rate
throughout life no definite wear out period (68
1.0 Why We Have to Do Maintenance
  • The United Airlines study showed that only about
    11 of the items included in the experiment
    (curves A, B and C) would benefit from setting
    operating limits, or from applying a repeated
    check of wear conditions. The other 89 would
  • Consequently, time of failure, or deterioration
    beyond useful levels could be predicted on only
    11 of the items.
  • Only components with definite life time limits
    and/or wear out periods will benefit from
    scheduled maintenance !
  • The required maintenance activity for these
    items can be spread out over the available time
    to even out the work load.

1.0 Why We Have to Do Maintenance
  • For the other 89 , these items will have to be
    operated to failure before replacement or repair
    is done.
  • This is unpredictable and would result in a need
    for maintenance at odd times i.e.. unscheduled
  • These characteristics of failure make it
    necessary to approach maintenance in a
    systematic manner, to reduce periods of
    unscheduled maintenance.
  • The aviation industry has developed three
    management techniques for handling in-service
    interruptions which occur where items must be
    operated to failure before maintenance can be

1.0 Why We Have to Do Maintenance
  • Redundant Systems
  • In redundant systems, if one unit fails, one or
    more backups are available to immediately take
    over the function

Example 1 Aircraft elevator hydraulic actuator.
1.0 Why We Have to Do Maintenance
  • 2. 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.
  • The vehicle can then continue in without any
    significant interruption in service.
  • The failed part can be discarded or repaired

1.0 Why We Have to Do Maintenance
  • 3. Minimum Equipment List (MEL)
  • This list allows a vehicle to be dispatched into
    service with certain items inoperative
    provided that the loss of the function does not
    affect the safety and operation of the flight.
  • These items are carefully determined by the
    aircraft manufacturer and must also be
    sanctioned by the appropriate regulatory
    authority during the early stages of vehicle
    design and test.
  • The manufacturer issues a master minimum
    equipment list (MMEL) which indicates all
    equipment and accessories available for a
    particular aircraft model.
  • The airline then customizes this document to
    produce its own MEL.

What you need to know for the exam !
  • Explain what entropy is and its relationship to
    the need for maintenance.
  • What is the role of an engineer in the context
    of entropy ?
  • What is the role of a mechanic in the context of
    entropy ?
  • With the aid of a sketch diagram, explain the
    relationship between entropy or perfection and
  • With the aid of a sketch diagram illustrating
    the relationship between reliability and time,
    explain what is meant by the designed-in level
    of perfection and the point at which scheduled
    maintenance is done.
  • With the aid of a sketch diagram, explain the
    relationship between perfection and cost.
  • Give some examples of failure rate patterns.
    What is the bath tub curve ?
  • Explain each of the three management techniques
    which have been developed by the aviation
    industry for handling in-service interruptions
    due to equipment failures. What failure rate
    curves characterize these types of failures ?

2.0 Development of Maintenance Programs
1.0 Why We Have to Do Maintenance
What is a component and what is a system ?
  • A collection of components organized to
    accomplish a specific function or set of
  • An assembly of various components designed to
    function as a whole.
  • A collection of interacting subsystems designed
    to satisfy a set of requirements.
  • So a system is composed of components, or
    smaller subsystems, and all of it is designed to
    provide one or more functions.
  • A component is the smallest part you cannot
    subdivide a component.

2.0 Development of Maintenance Programs
  • Introduction
  • We have seen in the first lecture that
    components and systems fail in different ways
    and at different rates.
  • This results in a requirement for unscheduled
    maintenance that is somewhat erratic and
  • There are periods high workloads and periods
    with no work these have to be managed to
    smooth out the workload and stabilize the
    manpower requirements.
  • The maintenance programs currently in use in
    commercial aviation were developed by the
    aviation industry using two diffeent approaches
  • the process-oriented approach, and
  • the task-oriented approach

2.0 Development of Maintenance Programs
  • The Process-Oriented Approach
  • This uses three primary maintenance processes to
    accomplish the scheduled maintenance actions
  • Hard-Time (HT)
  • Used for components or systems that have
    definite life limits. Item is removed at a
    predetermined interval, usually specified in
    either flight hours or flight cycles.
  • On-Condition (OC)
  • Used for components or systems that have
    detectable wear out periods. Item will be
    checked at specific intervals (in hours, cycles,
    or calendar time) to determine its remaining
  • Condition Monitoring (CM)
  • Used to monitor systems and components that
    cannot utilize either HT or OC processes.
    Involves monitoring of failure rates, removal
    rates, etc. to facilitate maintenance planning

2.0 Development of Maintenance Programs
  • HT and OC processes apply to items in categories
    A, B and C

A. Infant mortality constant or slightly rising
failure rate definite wear out period (4 ).
B. No infant mortality slightly rising failure
rate definite wear out period (2 ).
C. No infant mortality slightly rising failure
rate no definite wear out period (5 ).
HT definite life limits OC detectable wear
out periods
2.0 Development of Maintenance Programs
  • CM items are operated to failure and failure
    rates are tracked to aid in failure prediction
    or failure prevention efforts.
  • These are operate to failure items in
    categories D, E and F

D. Increasing failure rate at outset constant or
slightly rising failure rate no definite wear
out period (7 ).
E. No infant mortality constant failure rate
throughout life no definite wear out period (14
F. Infant mortality constant failure rate
throughout life no definite wear out period (68
CM no definite wear out period.
2.0 Development of Maintenance Programs
  • The Maintenance Steering Group (MSG) Approach
  • The modern approach to aircraft maintenance
    started with the Boeing Company in 1968.
  • It coincided with the introduction of the Boeing
    747 then the largest commercial airplane.
  • Six industry working groups analysed aircraft
  • structures
  • mechanical systems
  • engines and auxiliary power plants
  • electrical and avionics systems
  • flight controls and hydraulics
  • zonal configurations.

2.0 Development of Maintenance Programs
  • This analysis provided them with information on
    failure modes, failure effects and failure
  • The approach was called bottom up because it
    looked at the components as the most likely
    causes of equipment malfunction.
  • The purpose of the analysis was to determine
    which of the three processes (HT, OC or CM)
    would be required to repair the item and return
    it to service.
  • This resulted in the a generalized maintenance
    process called MSG-2 which could be applied to
    any aircraft, not just 747s.
  • The following table summarizes the steps
  • Note that the process is sligtly different for
    (a) systems and components, (b) structures and
    (c) engines

2.0 Development of Maintenance Programs
  • Process-Oriented Maintenance
  • The Hard-Time Process
  • Hard time is a failure prevention process.
  • It is applied to items
  • having a direct adverse effect on safety
  • subject to reliability degredation but having no
    possible maintenance check (e.g. rubber
  • The item has to be removed from the vehicle and
  • completely overhauled, or
  • partial overhauled, or
  • discarded
  • before exceeding a pre specified life time.

2.0 Development of Maintenance Programs
  • This life time or interval between each removal
    of the item may be specified in terms of
  • calendar time
  • engine or aircraft check intervals
  • operating cycles
  • flight hours
  • If a particular component fails at X hours of
    operation, ideally the component would be
    replaced at the last scheduled maintenance
    period prior to the accumulation of X hours.
  • This would give the airline the maximum service
    hours from the component and the component would
    never fail in service.

2.0 Development of Maintenance Programs
  • The On-Condition (OC) Process
  • With on-condition, the item is not removed
    periodically. Instead, it is subject to periodic
    inspections or tests.
  • The objective of the inspections or tests is to
    determine whether or not the item can continue
    in service.
  • If an item fails an OC check, only then is it
    removed for overhaul, repair, or replacement.
  • OC items are restricted to component / equipment
    / systems on which checks and tests can be
    applied without having to remove the item.
  • These OC checks must be performed within time
    limits (intervals) prescribed for each OC check.

2.0 Development of Maintenance Programs
  • The Condition Monitoring (CM) Process
  • Unlike HT and OC processes, CM does not really
    monitor the condition of a component.
  • CM systems consist of data collection and data
    analysis procedures.
  • For example, a CM process may collect data on
  • unscheduled removals of equipment from aircraft
    (i.e. due to some failure),
  • maintenance log entries,
  • pilot reports,
  • workshop findings,
  • sampling inspections,
  • mechanical reliability reports, and
  • other sources of maintenance data

2.0 Development of Maintenance Programs
  • The CM process is applied when neither the hard
    time nor the on-condition process can be applied.
  • CM is not a failure prevention process as are HT
    and OC.
  • CM components have to be operated to failure, and
    replacement of CM items is an unscheduled
    maintenance action.
  • Since CM items are operated to failure, these
    items must comply with the following conditions
  • A CM item has no direct, adverse effect on safety
    when it fails.
  • A CM item must not have any hidden function
    (i.e. that cannot be observed by flight crew).
  • A CM item must be included in a CM program.

What you need to know for the exam !
  • Can you explain what is meant by a component and
    system ?
  • What are the two main approaches developed by
    the aviation industry for developing maintenance
    programmes and what maintenance processes do
    they use ?
  • Can you explain MSG-2 ?
  • Can you explain Process-Oriented Maintenance ?

393SYS Airport Engineering Practice Lecture
3Development of MaintenancePrograms
2.0 Development of Maintenance Programs
  • Task Oriented Maintenance
  • These procedures are referred to as MSG-3.
  • MSG-3 is a modification of and an improvement on
    the MSG-2 approach.
  • MSG-2 was a bottom-up approach involves
    monitoring systems at their component level to
    detect failure conditions.
  • MSG-3 is a top-down approach which is used to
    identify suitable scheduled maintenance tasks to
    prevent failures and maintain the reliability of
    the system.

2.0 Development of Maintenance Programs
  • MSG-3 asks - how does a particular failure
    affect the operation of the aircraft ?
  • It does not matter whether a system, subsystem,
    or component fails.
  • What matters is how the failure affects the
    aircraft operation.
  • Failures are assigned one of two basic
  • Safety, or
  • Economic
  • The following diagram is a simplified version of
    the first step in the MSG-3 logic process

2.0 Development of Maintenance Programs
There are three categories of tasks developed by
the MSG-3 approach (a) airframe systems
tasks (b) structural item tasks (c) zonal tasks
2.0 Development of Maintenance Programs
  • A. Maintenance Tasks for Airframe Systems
  • Decision analysis results obtained using MSG-3
    assigns a combination of the following eight
  • Lubrication applying oil and grease to reduce
    friction and wear.
  • Servicing attending to basic needs of
    components and/or systems.
  • Inspection Examination of an item and
    comparison against a standard.
  • Functional Check Measurements are made to
    determine if each function of an item performs
    within specified limits.
  • Operational Check Determines if an item is
    fulfilling its intended purpose. Does not
    require measurements of tolerances.
  • Visual Check Observation used to determine is
    fulfilling its intended purpose. Does not require
    measurements of tolerances.
  • Restoration Returns an item to a specified
    standard. Varies from simple cleaning to complete
  • Discard Removes an item from service at a
    specified life limit.

2.0 Development of Maintenance Programs
  • B. Maintenace Tasks for Structural Items
  • Airplanes are subjected to three sources of
    structural deterioration
  • Environmental Deterioration Deterioration of an
    items strength or resistance to failure as a
    result of interaction with climate or the
  • Acidental Damage Deterioration of an item
    caused by
  • impact with some object which is not part of the
  • errors in manufacturing
  • damage during operation
  • damage during maintenance
  • Fatigue Damage The formation of cracks due to
    cyclic loading.

What you need to know for the exam !
  • Can you briefly describe the main
    characteristics of the MSG-3 approach to
    maintenance and how it differs from MSG-2 ?
  • Given the simplified logic diagram for MSG-3,
    could you trace a particular sequence of
    questions and arrive at a particular result ?
  • Could you identify or briefly describe some or
    all of the maintenance tasks identified in the
    three categories of tasks developed by the MSG-3
    approach ?
  • Given a simple schematic diagram of a commercial
    aircraft, could you explain what zonal
    maintenance refers to ?
  • If you were given a sample of one of the main
    certifications required for commercial aircraft,
    could you identify the main items of information
    they must include ?
  • Can you identify and briefly describe 5
    different types of maintenance documentation
    provided by aircraft manufacturers ?

393SYS Airport Engineering Practice Lecture
4Development of MaintenancePrograms
4.0 Documentation For Maintenance
  • Types of Documentation
  • Main types of documentation
  • Manufacturers Documentation ?
  • Regulatory Documentation
  • 3. Airline Generated Documentation

4.0 Documentation For Maintenance
  • Regulatory Documentation
  • In the United States, the FAA (Federal Aviation
    Administration) issues many documents on
    aircraft maintenance. The most significant ones
  • Federal Aviation Regulations (FARs)
  • Advisory Circulars (ACs)
  • Airworthiness Directives (ADs)
  • Notice Of Proposed Rule Making (NPRM)

This last one is issued by the FAA whenever the
FAA intends to change a FAR. It is issued in
advance of the change to give aviation industry
plenty of time to study and comment on the
proposed change.
4.0 Documentation For Maintenance
Federal Aviation Regulations (FARs) These are the
laws of the United States which relate to all
aspects of aviation including private, commercial
and experimental aircraft airports navigational
aids air traffic control training of pilots,
air traffic controllers, mechanics etc.
Example FAR
4.0 Documentation For Maintenance
  • Advisory Circulars (ACs)
  • Designed to help airline operators meet the
    requirements of FARs.
  • An AC often states that something is a means,
    but not the only means of complying with a
  • Airworthiness Directives (ADs)
  • The airworthiness directives are very important
    regulations issued by the FAA to correct an
    unsafe condition that exists in an
  • aircraft
  • aircraft engine
  • propeller,
  • aircraft appliance

4.0 Documentation For Maintenance
  • Aircraft owners or operators are required to
    maintain aircraft in compliance with all ADs.
  • Typically an AD will include
  • a description of the unsafe condition
  • the item to which the AD applies
  • the corrective action required
  • date of compliance
  • where to get additional information
  • information on alternative methods of compliance
    (if applicable)

Effective, November 12, 2002 Airworthiness
Directives Boeing Model 737 Series Airplanes
Applicability All Model 737 series airplanes
certificated in any category. To prevent an
uncommanded rudder hardover event and consequent
loss of control of the airplane due to inherent
failure modes, including single-jam modes, and
certain latent failure or jams combined with a
second failure or jam accomplish the following
4.0 Documentation For Maintenance
  • Airline Generated Documentation
  • Operations Specification (Ops Spec)
  • Written by the airline in accordance with strict
    FAA requirements.
  • The Ops Spec is required for each aircraft type
    flown by the airline.
  • It details the airlines maintenance,
    inspection, and operations programs.

4.0 Documentation For Maintenance
  • Technical Policies and Procedures Manual (TPPM)
  • The airlines Maintenance Engineering (ME)
    operations manual.
  • Defines exactly how all ME functions and
    activities will be carried out.
  • A detailed document may be several volumes.
  • Personnel in ME must be trained on the TPPM.

4.0 Documentation For Maintenance
  • Inspection Manual (IM)
  • Usually a chapter in the TPPM.
  • Contents relate to -
  • mechanic inspection tasks
  • QC inspector tasks
  • special inspections (hard landings, bird strikes,
  • airlines required inspection item (RII) program
  • paperwork and forms to carry out these functions

4.0 Documentation For Maintenance
  • Quality Assurance Manual (QAM)
  • This could be either
  • a special manual for QA auditors only, or
  • a separate chapter in the TPPM.
  • Defines procedures used in the annual QA audits
    conducted on the ME units, suppliers and
    outside contractors.
  • Includes formats for forms and reports to be
    used in the QA procedures.

4.0 Documentation For Maintenance
  • Minimum Equipment List (MEL)
  • The aircraft manufacturer produces the Master
    Minimum Equipment List (MMEL).
  • This includes all aircraft configurations
    available for a particular model of aircraft
    (e.g. Boeing 747-100, 747-200, etc.).
  • For some models of aircraft, customers can
  • engines from three different manufacturers
  • various auxiliary systems as buyer options
  • .. much of this is not applicable to some
  • The airline operator is therefore required to
    customize the MMEL for their aircraft engine /
    airframe configurations.
  • The customized MMEL becomes the MEL.
  • Copies of this MEL must be carried in each
    aircraft for flight crew reference.

4.0 Documentation For Maintenance
  • Task Cards
  • Certain tasks defined in the AMM for -
    removal/installation, testing, servicing and
    similar maintenance - are reproduced on separate
    cards or sheets so that the mechanic can perform
    a particular maintenance task without having to
    carry the entire maintenance manual around with
  • These tasks may call for the mechanic to open
    panels, set certain circuit breakers in or
    out, turn other equipment on or off, etc.,
    before they can do the maintenance task, and
    then they must reverse these steps when they
    have completed the maintenance task.
  • However, much of the work done during an
    aircraft check involves a combination of several
    tasks applied in the same area of the aircraft.
  • To avoid repeating the same tasks and
    unnecessary opening and closing of the same
    panels, most airlines write their own task cards
    to combine these maintenance activities.

What you need to know for the exam !
  • Can you identify the four main types of
    regulatory documentation issued by the FAA in
    the United States ?
  • Explain, briefly, the purpose of the following
    Federal Aviation Regulations (FARs), Advisor
    Circulars, Airworthiness Directives and Notices
    Of Proposed Rule Making (NPRMs).
  • Provide a brief description of the different
    types of documentation generated by airlines.
  • What are the five objectives of an aviation
    maintenance programme ?
  • Explain, briefly, the nature of the different
    areas relating to aviation maintenance which
    contribute to the five objectives of an aviation
    maintenance programme.

393SYS Airport Engineering Practice Lecture
5Engineering Production
6.0 Engineering
  • Engineering Department Functions
  • Each model of aircraft has an initial
    maintenance program developed by an Industry
    Working Group.
  • The initial maintenance program is a generalized
    program and must be tailored to the individual
    airline operators requirements from the very
  • The manufacturer produces the FAA approved MRB
    report and a maintenance planning document.
  • It is the responsibility of the engineering
    department of the airline to package these tasks
    into workable units based on factors such as
  • time, space, personnel, fleet schedules, and
    overall airline capabilities.

6.0 Engineering
  • Aircraft Maintenance Checks (from
  • Aircraft maintenance checks are periodic checks
    that have to be done on all aircraft after a
    certain amount of time or usage.
  • Airlines casually refer to these checks as one
    of the following A check, B check, C check, or
    D check.
  • A and B checks are lighter checks, while C and D
    are considered heavier checks.
  • A Check This is performed approximately every
  • This check is usually done overnight at an
    airport gate.

6.0 Engineering
  • The actual occurrence of this check varies by
    aircraft type, the cycle count (takeoff and
    landing is considered an aircraft "cycle"), or
    the number of hours flown since the last check.
  • The occurrence can be delayed by the airline if
    certain predetermined conditions are met.
  • B Check This is performed approximately every 3
  • This check is also usually done overnight at an
    airport gate. A similar occurrence schedule
    applies to the B check as to the A check.
  • C Check This is performed approximately every
    12-18 months.
  • This maintenance check puts the aircraft out of
    service and requires plenty of space - usually
    at a hangar at a maintenance base.

6.0 Engineering
  • The schedule of occurrence has many factors and
    components as has been described, and thus
    varies by aircraft category and type.
  • D Check This is the heaviest check for the
  • This check occurs approximately every 4-5 years.
  • This is the check that, more or less, takes the
    entire airplane apart for inspection.
  • This requires even more space and time than all
    other checks, and must be performed at a
    maintenance base.

6.0 Engineering
  • The A and B checks are no problem for airlines
    because they do not take the aircraft out of
  • Large airlines have a large fleet of aircraft -
    enough for the airline to schedule people and
    facilities for regular C checks e.g. one
    airplane per week or month.
  • In small airlines, there are not enough
    airplanes or manpower for the regular scheduling
    of C checks.
  • To solve this problem, the C check is divided
    into parts, called phases, and each phase is
    conducted separately.
  • For example, a C check could be divided into
    four phases C1, C2, C3 and C4 each one
    carried out every 3 months until the entire C
    check is performed.

6.0 Engineering
  • Alternatively, a C check could be divided into
    12 packages with one package completed every
    month together with the A check.
  • In both cases, the manpower utilization is more
    constant throughout the year.
  • The airline engineering department is
    responsible for selecting the tasks to be done,
    for packaging the tasks into workable packages,
    and for ensuring that all task time limits are
  • The Production, Planning and Control
    department is then responsible for scheduling
    the checks.
  • The tasks to be performed by the maintenance
    unit of the airline at any of these checks can
    be quite detailed.
  • To endure that they are carried out correctly,
    tasks cards are issued to the mechanics.

7.0 Production Planning and Control
  • Introduction
  • The Production Planning and Control (PPC)
    activity within an airline is one of the key
    organizations within ME.
  • It is actually the heart of the maintenance
  • The title implies two functions planning and
  • Actually, PPC has three primary functions
    forecasting, planning, and control.
  • Forecasting includes the estimated maintenance
    workload for the long term and short term based
    on the existing fleet and business plans, and on
    any known changes in these for the forecast

7.0 Production Planning and Control
  • Planning involves the scheduling of upcoming
    maintenance and includes the planning and
    scheduling of all manpower, parts, facilities,
    and time frame requirements.
  • Control allows adjustment of the plan and keeps
    (or attempts to keep) the check on schedule.
  • There are several methods of adjusting the plan,
  • deferral of maintenance to a later check,
  • addition of personnel to complete the work,
  • outsourcing the work to a contractor
  • Feedback from a check allows PPC to adjust the
    planning effort for future checks.

7.0 Production Planning and Control
  • Without planning, action would be impulsive and
    produce unpredictable results.
  • The diagram below illustrates how work in
    expended on a typical project with and without
    proper planning

7.0 Production Planning and Control
  • The preliminary planning consists of the
    development of a maintenance program and its
  • With proper planning, once the check has begun,
    the work progresses smoothly (dashed yellow
  • Without preliminary planning, the effort swells
    as the work progresses, mostly due to unexpected
    events and delays (solid red line).

7.0 Production Planning and Control
  • Example for C Check
  • Normally, a C check requires about 4 or 5 days.
  • A new airline operator started to consult the
    maintenance manual for the C check one week
    before the check was due.
  • Without adequate preplanning, the C check took 4
    weeks to perform !
  • The goals of PPC are -
  • to maximize the ME contribution to the airline
  • to plan and organize work prior to execution
  • to adjust plans and schedules to meet changing

7.0 Production Planning and Control
  • Production Planning
  • The goal of ME is to deliver airworthy vehicles
    to the flight department in time to meet the
    flight schedule, with all maintenance activities
    completed or properly deferred.
  • The airline engineering department will have
    developed the maintenance plan from the MRB
    (Maintenance Review Board report) or Ops Specs
    document and divided the work into appropriate
    work packages indentifying
  • the tasks to be done
  • the intervals at which they will be done, and
  • the manpower requirements for each task.
  • The check package schedule for a typical
    mid-sized airline is shown in the following

7.0 Production Planning and Control
  • Maintenance Tasks for Less-than-A-Check
  • Certain items in the MRB report must be checked
    daily, bi- weekly, and weekly.
  • The scheduling is the responsibility of PPC.
  • These checks can be scheduled overnight, or at
    certain turn- around times, or may be included in
    the A checks.
  • This is up to the airline and is usually
    determined by local conditions and man-power
  • Airlines can experience problems if they defer
    these tasks day after day due to heavy work
  • The deadline for completion gets nearer and
    nearer and, finally, the airline has to take the
    aircraft out of service for several hours to get
    the work done without exceeding FAA time limits.
    These delays can be costly.

7.0 Production Planning and Control
  • Multiple Checks
  • Some MRB items are done at intervals like every
    other every third check. This is true for A C
    checks. That means that different A check
    have different task set and require different
    amount of time depending on where that A check
    is in the maintenance cycle.
  • The following table shows a typical aircraft A
    check and C check schedule

From Aviation Maintenance Management,
H.A.Kinniston, McGraw-Hill 2004.
7.0 Production Planning and Control
  • Every C check includes all the A check
  • The C check items can also be scheduled for
    longer intervals.
  • A chart similar to the one on the previous slide
    can be drawn for multiple C checks.
  • Phased Checks
  • These are different from multiple checks.
  • An A check may be split into two phases, each
    one performed on successive nights to minimize
    maintenance crew needs and down time.
  • The right side of an aircraft might be done on
    the first phase (called an A1 check and the
    left side on the second phase (the A2 check).

7.0 Production, Planning and Control
  • A C check may be broken down into four parts
    (C1, C2, C3, and C4) and performed every 3
    months or so depending on the full C check
  • The C check can also be divided into 12 parts,
    with one part being completed each month (C1,
    C2, C12).
  • The table on the following slide shows a typical
    airline estimate for the man-hours planned for a
    C check on the Airbus A300B4.
  • The check will consist of three categories of
    task routine, variable routine, and
  • Routine tasks are identified in the MRB report
  • Variable routine tasks vary from one check to
    another and from one aircraft to another.
  • Nonroutine tasks are generated by the
    accomplishment of other, routine tasks.

What you need to know for the exam !
  • Why do all airlines require a maintenance
    department, regardless of whether or not they
    actually do the maintenance themselves ?
  • Explain the difference between mechanics and
    engineers in terms of their role in aircraft
  • What is the MRB report, who is responsible for
    producing it and what are airlines required to
    do with it ?
  • Explain, briefly, what is meant be aircraft A,
    B, C and D checks.
  • What approach is adopted by small airlines in
    conducting C checks ?
  • What issues need to be addressed in evaluating
    new (used) aircraft for an airline fleet ?
  • Explain, briefly, the function of Production,
    Planning and Control department within an
    airline ?
  • What is the relationship between Engineering and
    PPC in an airline ?
  • Explain the purpose of Production Planning.
  • Explain Multiple Checks and Phased Checks
    and also the difference between the two.

Aviation reliabilityPrograms calculation
  • Kinnison, Chapter 19

June 09
Reliability Program (for maintenance)
  • A set of rules and practices for managing and
    controlling a maintenance program. The main
    function is to monitor the performance of the
    vehicles and their associated equipment and call
    attention to any need for corrective action.
  • Additional functions
  • Monitor the effectiveness of those corrective
  • Provide data to justify adjusting the maintenance
    interval or maintenance program procedure as

June 09
Maintenance programs have four types of
  • Statistical reliability
  • Historical reliability
  • Event-oriented reliability
  • Dispatch reliability

June 09
Statistical reliability
  • Based upon collection and analysis of events
    such as failure, removal, and repair rates of
    systems or components.

June 09
Historical reliability
  • Comparison of current event rates with those of
    past experience. Commonly used when new
    equipment is introduced and no established
    statistic is available.

June 09
Event-oriented reliability
Blade penetrated fuselage above window
  • Events like bird strikes, hard landing, in-flight
    shutdowns (IFSD), lighting strikes or other
    accidents that do not occur on a regular basis
    and therefore produce no useable statistical or
    historical data. In ETOPS, FAA designated
    certain events to be tracked as event-oriented
    reliability program. Each occurrence of the
    events must be investigated to determinate the
    cause to prevent recurrence.
  • IFSD causes for example due to flameout,
    internal failure, crew-initiated shutoff, foreign
    object ingestion, icing, inability to obtain
    and/or control desired thrust.

June 09
Dispatch reliability
  • Measurement of an airline operation respect to
    on-time departure. It receives considerable
    attention from regulatory authorities(e.g. FAA),
    airlines and passengers. Actually, it is just a
    special form of the event-oriented reliability

June 09
Elements of a Reliability Program
  • Data collection
  • Problem area alerting
  • Data display
  • Data analysis
  • Corrective actions
  • Follow-up analysis
  • Monthly report

June 09
Data Collection allows operator to compare
present performance with the past, typical data
type are
  • Flight time and cycle for each aircraft
  • Cancellations and delays over 15 minutes
  • Unscheduled component removals
  • Unscheduled engine removals
  • In-flight shutdowns of engines
  • Pilot reports or logbook write-ups
  • Cabin logbook write-up
  • Component failures (shop maintenance)
  • Maintenance check package findings
  • Critical failures

June 09
Problem detection alerting systems
  • alerting systems for quick identify areas where
    performance is significantly different from
    normal so that possible problems can be
    investigated. Standards for event rates are set
    according to past performance.

June 09
  • Basic Calculation Application

June 09
f(t), the failure density function over a time
interval t1, t2 and is defined as the ratio of
the number of failures occurring in the interval
to the size of the original population, divided
by the length of the time interval
Where n(t) is the number of the fault survivors
at time t The f(t) can measure the overall speed
at which failures are occurring
June 09
Z(t), the failure rate, or the Hazard function is
the probability that a failure occurs in some
time interval t1, t2, given that the system has
survived up to time t. It is the ratio of the
number of failures occurring in the interval to
the size of the original population, divided by
the length of the time interval
The Z(t) can measure the instantaneous speed of
June 09
F(t) is the probability of failure ( Cumulative
Distribution) R(t) is the probability of
success ( Reliability) Þ F(t) R(t) 1
June 09
Failure data for 10 hypothetical electrical
Failure Number
Operating time, h
1 8 2 20 3 34 4 46 5 63 6
86 7 111 8 141 9 186 10 266
June 09
10-9/10 / (8-0) 1//10/8 0.0125
8/1 10 80
20/2 10 100
June 09
Implementing Fault Tolerance
  • Hardware - Triple-Modular Redundancy (TMR)
  • Hardware unit is replicated three (or more) times
  • Output is compared from three units
  • If one unit fails, its output is ignored
  • Space Shuttle is a classic example

Machine 1
Machine 2
Output Comparator
Machine 3
June 09
Implementing Fault Tolerance (2)
  • Using Software
  • N-Version programming
  • Have multiple teams build different versions of
    the software and then execute them in parallel
  • Assumes teams are unlikely to make the same
  • Not necessarily a valid assumption, if teams all
    work from the same specification

June 09
N-Version Programming
  • Commonly used approach in railway signaling,
    aircraft systems reactor protection system

June 09
Event diagram for AND-OR configuration
June 09
  • Rs Reliability of the system.
  • R1XR2 where R1 R2 are the reliability
    of components C1 C2.
  • Rs with n components arranged in logical .AND.
  • then,
  • Rs R1 X R2 X X Rn

June 09
  • Rs Reliability of the system.
  • R1, R2, ..Rn Reliability of component 1, 2,
  • in this case, it is easier to calculate by the
    probability of failure F
  • Fs (1 - Rs)
  • F1 (1 - R1) F2 (1 - R2)
  • Fs F1 F2
  • (1 - R1) (1 - R2)
  • Rs 1 - Fs
  • 1 - (1 - R1) (1 - R2) (1 - Rn)
  • for n components arranged in logical .OR.

June 09
Reliability Acronyms
  • MTBF - Mean Time Between Failures
  • MTTF - Mean Time To Failure
  • MTTR - Mean Time To Repair
  • Many people consider it to be far more useful
    than measuring fault rate per LOC

June 09
Time (up) A(T) ------------------------------
------------ Time(up) Time(down)
MTTF MTTF -------------------
------- -------------- MTTF MTTR
Where MTTF Mean Time To Fail MTTR
Mean Time To Repair MTBF MTTF MTTR Where
MTBF Mean Time Between Failure
June 09
Failure rate and Reliability during the random
failure period
Rs e t/m e -tl where Rs
Probability of failure free operation for period
t e 2.718 t specified period of
failure free operation m mean time between
failure (MTBF) l failure rate 1/m
June 09
Quality Assurance ISO9000 Quality Standard
  • Kinnison, Chapter 17

June 09
ISO 90012000 Exclusionref. 1.2 4.2.2 a
June 09
Example of ISO 90012000 Exclusion Customer
property controlled by a bank.
  • Situation  
  • A bank provides a variety of services to its
    customers and chooses to implement a QMS only for
    its Internet banking services. For this service
    the bank has claimed conformity to ISO 90012000.
    The bank clearly states in its Quality Manual
    which services are covered by the QMS. The bank
    applies all the requirements of ISO 90012000 for
    the realization of its Internet banking services,
    with the exception of sub-clause 7.5.4 Customer
    property. The bank does not feel that it has
    possession of any customer property as part of
    its Internet banking services and has stated this
    in the justification for the exclusion of
    sub-clause 7.5.4 Customer property from its QMS.
  • Issue(s)
  • Can the bank exclude sub-clause 7.5.4 Customer
    property from its QMS and claim conformity to ISO

June 09
Example of ISO 90012000 Exclusion Customer
property controlled by a bank. (conti.)
  • Issue(s)
  • Can the bank exclude sub-clause 7.5.4 Customer
    property from its QMS and claim conformity to ISO
  • Analysis and Conclusion
  • The decision made by the bank to exclude
    sub-clause 7.5.4 Customer property was not
    justified because the bank does receive
    information from its customers such as personal
    and confidential data. ISO 9001, 7.5.4 Customer
    property requires an organization to exercise
    care with customer property while it is under the
    organizations control or being used by the
    organization. In this situation, the banks
    customers provide important information in
    confidence when using the service, which
    constitutes Customer property. Therefore the
    bank has to address the requirements for customer
    property in its QMS.

June 09
Requirement of Quality Assurance (QA)
  • For each type of aircraft flown, airlines must
    generate the Operations Specifications (Ops
    Specs) that establish the maintenance and
    inspection programs to be used to keep the
    aircraft in an airworthy condition. It is
    referred as the Continuous Airworthiness
    Maintenance Program (CAMP) section in the Ops
  • In addition, Federal Aviation Regulation (FAR)
    121.373 Continuing Analysis and Surveillance
    System (CASS) provides an additional requirement
    as follows Each certification holder shall
    establish and maintain a system for the
    continuing analysis and surveillance of the
    performance and effectiveness of its inspection
    program and the program covering other
    maintenance, preventive maintenance, and
    alternations and for the correction of any
    deficiency in those programs, regardless of
    whether those programs are carried out by the
    certificate holder or another person.

June 09
Functions of QA
  • Administration and management of QA and CASS
  • Conduct QA audit
  • Maintenance of technical records
  • Liaison with the regulatory authority

June 09
Quality Management System Quality Manuals
It is a generic approach evolved throughout the
years. It is an efficient way to organize an
Quality System and is specified in ISO90012000
4.2.1 5.3
June 09
Entities on ISO9001 1994 vs. 2000ref. c 3
subcontractor Supplier
Purchaser Customer
Supplier Organization shall do, should do, May
Product / Service
Supply Chain
June 09
ISO 9000 language of Standardsref. ISO 9000
Introduction and Support Package Guidance on
the Terminology used in ISO 90012000 and ISO
  • shall or shall not is used to express a
    provision that is binding between two or more
    parties, means it is necessary, it is
    required to
  • should or should not express a recommendation
    among several possibilities without mentioning or
    excluding others.
  • may or need not indicate a course of action
    permissible within the limits of ISO 9001
  • can or cannot refers to the ability of the
    user of the standard.

June 09
Quality Audit and ISO9000 Quality Standard
  • Kinnison, Chapter 17

June 09
ISO 9000 Audit
  • First Party Auditing
  • Audits carried out by the Organization on its own
    systems (e.g. Internal Audit by QA unit)
  • Second Party Auditing
  • Audits carried out by the Customer on the
    Organization prior to or after contract
    placement.(e.g. by Government QA unit)
  • Third Party Auditing
  • Audits carried out by independent accredited

June 09
Purpose of quality audit
  • 1st Party audit
  • To confirm compliance with the rules.
  • To ensure that the rules are implemented in an
    effective manner.
  • To identify the system is applicable to the
    overall objectives of the organization
  • 2nd Party audit
  • To decide whether future contracts can be
    awarded or
  • To determine whether existing contractual
    performance is satisfactory.
  • 3rd Party audit
  • Mainly for the purpose of granting or to confirm
    continuation of (for ongoing surveillance audit)
    ISO9001 certification.

June 09
Sample Audit Checklist
June 09
Quality Audit Tool - Check List
  • Check List is a collection of simple questions.
    It help to focus the mind on the task in hand and
    ensure that full coverage is obtain. However,
    audits based on them can be very shallow, taking
    little account of the specific circumstance of
    what is being audit
  • Check List can be made from
  • Based on recognized quality standards
  • Developed around departments operating system
  • Based on company standards and procedures
  • Based on product/customer requirements

June 09
Translate IS0 9001 Standard into High Level
  • 6.2 Human resources
  • 6.2.1 General
  • Personnel performing work affecting product
    quality shall be competent on the basis of
    appropriate education, training, skills and
  • High Level Requirements
  • Personnel performing work affecting product
    quality shall be competent
  • Personnel performing work affecting product
    quality shall be competent on the basis of
    appropriate education.
  • Personnel performing work affecting product
    quality shall be competent on the basis of
    appropriate training.
  • Personnel performing work affecting product
    quality shall be competent on the basis of
    appropriate skills.
  • Personnel performing work affecting product
    quality shall be competent on the basis of
    appropriate experience.

June 09
Creating check-list (Based on ISO 90012000 6.2.1)
June 09
Non conformance report - example
  • ISO9001 Standard Clause Number
  • ISO 9001 2000,C 4.2.3d
  • Non Compliance
  • Drawing DT132 Issue E in use in workshop area,
    latest issue according to central register is F.

June 09
The What and the How
  • The Whats in
  • ISO90012000-c7.5.5 Preservation of product The
    organization shall preserve the conformity of
    product during internal processing and delivery
    to the intended destination. This preservation
    shall include identification, handling,
    packaging, storage and protection. Preservation
    shall also apply to the constituent parts of a
  • The Hows in Organization
  • Chickens travel to the market in stacked, tightly
    packed crates. Dirt and contamination can
    spread. Temperature fluctuation and delays
    during transport may cause problems
  • How does the shipper avoid the spread of dirt and
    contamination during shipment?
  • How does the chicken truck assure that
    temperature limit do not exceed?

June 09
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