SIST EN 60706-2:2007

SLOVENSKI STANDARD
01-januar-2007
Vzdrževalnost opreme - 2. del: Zahteve za vzdrževalnost in študije vzdrževalnosti v
fazi snovanja in razvoja (IEC 60706-2:2006)
Maintainability of equipment -- Part 2: Maintainability requirements and studies during the
design and development phase
Instandhaltbarkeit von Geräten -- Teil 2: Instandhaltbarkeitsanforderungen und Studien
in der Entwicklungsphase
Maintenabilité de matériel -- Partie 2: Exigences et études de maintenabilité pendant la
phase de conception et de développement
Ta slovenski standard je istoveten z: EN 60706-2:2006
ICS:
03.100.40 Raziskave in razvoj Research and development
21.020 =QDþLOQRVWLLQQDþUWRYDQMH Characteristics and design of
VWURMHYDSDUDWRYRSUHPH machines, apparatus,
equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 60706-2
NORME EUROPÉENNE
June 2006
EUROPÄISCHE NORM
ICS 03.120.01; 21.020
English version
Maintainability of equipment
Part 2: Maintainability requirements and studies
during the design and development phase
(IEC 60706-2:2006)
Maintenabilité de matériel  Instandhaltbarkeit von Geräten
Partie 2 : Exigences et études de Teil 2: Instandhaltbarkeitsanforderungen
maintenabilité pendant la phase de und Studien in der Entwicklungsphase
conception et de développement (IEC 60706-2:2006)
(CEI 60706-2:2006)
This European Standard was approved by CENELEC on 2006-05-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, the Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2006 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60706-2:2006 E
Foreword
The text of document 56/1090/FDIS, future edition 2 of IEC 60706-2, prepared by IEC TC 56,
Dependability, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 60706-2 on 2006-05-01.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
(dop) 2007-02-01
national standard or by endorsement
– latest date by which the national standards conflicting
(dow) 2009-05-01
with the EN have to be withdrawn
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60706-2:2006 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 60300-1 NOTE  Harmonized as EN 60300-1:2003 (not modified).
IEC 60300-2 NOTE  Harmonized as EN 60300-2:2004 (not modified).
IEC 60300-3 NOTE  Harmonized in 60300-3 series (not modified).

__________
- 3 - EN 60706-2:2006
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

IEC 60050-191 1990 International Electrotechnical Vocabulary - -
(IEV)
Chapter 191: Dependability and quality of
service
1) 2)
IEC 60300-3-1 - Dependability management EN 60300-3-1 2004
Part 3-1: Application guide - Analysis
techniques for dependability - Guide on
methodology
1) 2)
IEC 60300-3-3 - Dependability management EN 60300-3-3 2004
Part 3-3: Application guide - Life cycle costing

IEC 60300-3-10 2001 Dependability management - -
Part 3-10: Application guide - Maintainability

1)
IEC 60300-3-11 - Dependability management - -
Part 3-11: Application guide - Reliability
centred maintenance
1) 2)
IEC 60300-3-12 - Dependability management EN 60300-3-12 2004
Part 3-12: Application guide - Integrated
logistic support
1) 2)
IEC 60300-3-14 - Dependability management EN 60300-3-14 2004
Part 3-14: Application guide - Maintenance
and maintenance support
1)
IEC 60706-3 - Maintainability of equipment - -
Part 3: Verification and collection, analysis
and presentation of data
1)
IEC 60706-5 - Guide on maintainability of equipment - -
Part 5 - Section 4: Diagnostic testing

1) 2)
IEC 60812 - Analysis techniques for system reliability - EN 60812 2006
Procedure for failure mode and effects
analysis (FMEA)
1) 2)
IEC 61025 - Fault tree analysis (FTA) HD 617 S1 1992

1) 2)
IEC 61160 - Design review EN 61160 2005

1)
Undated reference.
2)
Valid edition at date of issue.

Publication Year Title EN/HD Year
IEC 61649 1997 Goodness-of-fit tests, confidence intervals - -
and lower confidence limits for Weibull
distributed data
NORME CEI
INTERNATIONALE
IEC
60706-2
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2006-03
Maintenabilité de matériel –
Partie 2:
Exigences et études de maintenabilité
pendant la phase de conception et
de développement
Maintainability of equipment –
Part 2:
Maintainability requirements and studies
during the design and development phase

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For price, see current catalogue

60706-2  IEC:2006 – 3 –
CONTENTS
FOREWORD.7
INTRODUCTION.11

1 Scope.13
2 Normative references .13
3 Terms, definitions and acronyms .15
3.1 Terms and definitions .15
3.2 Acronyms .17
4 General approach.17
5 Principle of maintainability.19
6 Maintainability activities in the life cycle .19
6.1 General .19
6.2 Concept and definition phase .21
6.3 Design and development phase.21
6.4 Manufacture and installation phase .23
6.5 Operation and maintenance phases .23
6.6 Disposal phase.23
7 Specification of maintainability requirements .25
7.1 Statement of maintainability requirements .25
7.2 Maintainability characteristics.27
7.3 Constraints.31
7.4 Maintainability programme requirements .33
7.5 Verification .33
8 Maintainability studies in the design and development phase .35
8.1 General .35
8.2 Objectives .35
8.3 Maintainability studies in the design process .35
8.4 Analysis tools and procedures.45
9 Design support .59
9.1 Liaison .59
9.2 Design criteria and check-lists.61
9.3 Design reviews.63

Annex A (informative) Maintainability allocation .67
Annex B (informative) Example of a maintainability allocation .81
Annex C (informative) Example of allocation of reliability values and maintenance
strategy selection for a system with non-constant failure rate .87

Bibliography.101

60706-2  IEC:2006 – 5 –
Figure 1 – Maintainability studies in the design process.41
Figure 2 – Hardware level maintainability block diagram .49
Figure 3 – Basic steps in maintainability prediction .53
ACMT ACMT
 
50 95
Figure A.1 – = f .77
 
MACMT MACMT
 
Figure A.2 – Maintainability allocation to sub-item level .79
Figure B.1 – Functional level diagram .83
Figure C.1 – Weibull plot of the components in the system .99

Table 1 – Examples of quantitative maintainability characteristics.27
Table 2 – Detailed tasks in maintainability studies .43
Table A.1 – M allocation to sub-item level.75
Table B.1 – Allocation table .85
Table C.1 – Comparison of costs .97

60706-2  IEC:2006 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MAINTAINABILITY OF EQUIPMENT –

Part 2: Maintainability requirements and studies
during the design and development phase

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60706-2 has been prepared by IEC technical committee 56:
Dependability.
This second edition cancels and replaces the first edition, published in 1990, and constitutes
a technical revision.
The major technical changes with regard to the first edition concern the inclusion of the
original Section Two from IEC 60706-1:1982 entitled: Maintainability requirements in speci-
fications and contracts, as well as the original mathematical Annex A from IEC 60706-6:1994,
entitled Maintainability allocation.

60706-2  IEC:2006 – 9 –
The text of this standard is based on the following documents:
FDIS Report on voting
56/1090/FDIS 56/1101/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
IEC 60706 consists of the following parts, under the general title Maintainability of equipment:
NOTE Each part outlines the application of specific techniques to implement a maintainability programme.
Part 1: Introduction, requirements and maintainability programme
Part 2: Maintainability requirements and studies during the design and development phase
Part 3: Verification and collection, analysis and presentation of data
Part 4: Guide to maintenance and maintenance support planning
Part 5: Diagnostic testing
Part 6: Statistical methods in maintainability evaluation

The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
60706-2  IEC:2006 – 11 –
INTRODUCTION
Maintainability is a characteristic that defines the ease with which an item can be maintained
and supported during its period of use. Maintainability has to be built into an item during the
design and development phase and it is therefore important that maintainability requirements
be established as part of the initial specification.
The IEC 60706 series of standards is intended to give guidance on how a designer should
best incorporate high standards of maintainability into a product so that the cost of
maintenance is reduced to an acceptable level. It is also important to ensure that the
necessary maintenance can be undertaken to keep the product in a safe condition and that it
can be operated to its required performance.
This International Standard gives an introduction to the concept of maintainability, and
guidance as to how maintainability can be incorporated into specifications and contracts and
how maintainability should be considered as part of the design process. It forms part of a
hierarchy of standards on dependability as described below.
IEC 60300-1 and IEC 60300-2 are the IEC top-level standards that provide guidance on how
to incorporate dependability, including reliability, availability and maintainability, into
manufactured products. IEC 60300-3-10 is the top-level standard on maintainability, serving
as an application guide and which forms part of the IEC 60300-3 series of standards. It can be
used to implement a maintainability programme covering the initiation, development and in-
service phases of a product, which form part of the tasks described in IEC 60300-2. It also
provides guidance on how the maintenance aspects of the tasks should be considered in
order to achieve optimum maintainability.

60706-2  IEC:2006 – 13 –
MAINTAINABILITY OF EQUIPMENT –

Part 2: Maintainability requirements and studies
during the design and development phase

1 Scope
This part of IEC 60706 examines the maintainability requirements and related design and use
parameter, and discusses some activities necessary to achieve the required maintainability
characteristics and their relationship to planning of maintenance. It describes the general
approach in reaching these objectives and shows how maintainability characteristics should
be specified in a requirements document or contract.
It is not intended to be a complete guide on how to specify or to contract for maintainability.
Its purpose is to define the range of considerations when maintainability characteristics are
included as requirements for the development or the acquisition of an item.
The standard goes on to describe maintainability studies in the preliminary and detailed
design phases and their relationships to other maintainability and maintenance support tasks,
described in associated standards. Maintainability considerations in design reviews are also
included.
It is intended that customers acquiring items of equipment will find this standard useful in
assisting them to define their maintainability objectives and associated maintainability
programmes.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050(191):1990, International Electrotechnical Vocabulary (IEV) – Chapter 191:
Dependability and quality of service
IEC 60300-3-1, Dependability management – Part 3-1: Application guide – Analysis
techniques for dependability – Guide on methodology
IEC 60300-3-3, Dependability management – Part 3-3: Application guide – Life cycle costing
IEC 60300-3-10:2001, Dependability management – Part 3-10: Application guide – Maintain-
ability
IEC 60300-3-11, Dependability management – Part 3-11: Application guide – Reliability
centred maintenance
60706-2  IEC:2006 – 15 –
IEC 60300-3-12, Dependability management – Part 3-12: Application guide – Integrated
logistic support
IEC 60300-3-14, Dependability management – Part 3-14: Application guide – Maintenance
and maintenance support
IEC 60706-3, Guide on maintainability of equipment – Part 3: Sections Six and Seven –
Verification and collection, analysis and presentation of data
IEC 60706-5, Guide on maintainability of equipment – Part 5 – Section 4: Diagnostic testing
IEC 60812, Analysis techniques for system reliability – Procedure for failure mode and effects
analysis (FMEA)
IEC 61025, Fault tree analysis (FTA)
IEC 61160, Design review
IEC 61649, Goodness-of-fit tests, confidence intervals and lower confidence limits for Weibull
distributed data
3 Terms, definitions and acronyms
For the purposes of this document, the terms and definitions given in IEC 60050(191) apply,
together with the following:
3.1 Terms and definitions
3.1.1
maintainability (performance)
ability of an item under given conditions of use, to be retained in, or restored to, a state in
which it can perform a required function, when maintenance is performed under given
conditions and using stated procedures and resources
NOTE The term "maintainability" is also used as a measure of maintainability performance (see 191-13-01).
[IEV 191-02-07:1990]
3.1.2
maintainability
probability that a given maintenance action, for an item under given conditions of use, can be
carried out within a stated time interval, when the maintenance is performed under stated
conditions and using stated procedures and resources
NOTE The term "maintainability" is also used to denote the maintainability performance quantified by this
probability (see 191-02-07:1990).
[IEV 191-13-01:1990]
___________
1 A second edition is due to be published shortly under the revised title “Maintainability of equipment – Part 3:
Verification and collection, analysis and presentation of data”.

60706-2  IEC:2006 – 17 –
3.1.3
maintenance
combination of all technical and administrative actions, including supervision actions, intended
to retain an item in, or restore it to, a state in which it can perform a required function
[IEV 191-07-01:1990]
3.1.4
maintenance concept
interrelationship between the maintenance echelons, the indenture levels and the levels of
maintenance to be applied for the maintenance of an item
3.1.5
maintenance policy
general approach to the provision of maintenance and maintenance support based on the
objectives and policies of owners, users and customers
3.2 Acronyms
BITE built-in test equipment
FMEA failure modes and effects analysis
FTA fault tree analysis
ILS integrated logistic support
LCC life cycle cost
LRU line replaceable unit
LSA logistic support analysis
MART mean active repair time
MTTR mean time to repair (or restoration or recovery)
RCM reliability centred maintenance
SSI software significant item
4 General approach
An important portion of the cost of using an item is the total resources spent on those tasks
necessary to retain an item in, or restore it to, a satisfactory condition. This total effort is
related to the number of these tasks, their complexity and duration.
The design of an item shall ensure three things, namely:
a) that it achieves the performance required of it;
b) that it is reliable;
c) that it is maintainable.
The second and third of these characteristics directly affect the maintenance effort which shall
be expended on an item in that the achieved reliability reflects the frequency of unscheduled
maintenance and the maintainability reflects the effort necessary to undertake all
maintenance.
60706-2  IEC:2006 – 19 –
Therefore actions performed during the design of an item and intended to affect the failure
rate and the severity of the failures call mainly for reliability techniques, while those intended
to affect the preventive and corrective maintenance and the duration, cost and support
requirements of maintenance tasks call mainly for maintainability techniques.
An item that can be maintained easily and is supported by a competent and efficient
maintenance organization has a greater availability and a reduced life cycle cost than one that
does not have these attributes. The degree of effort that is put into achieving good
maintainability and an efficient support organization depends on the type of product and the
use to which it is put, and is based on operational, economic and safety factors.
During the design phase, components with wear out must be identified, and their life time be
determined, for example, by using Weibull analysis (see IEC 61649). The trade-off between
components with higher life time versus the cost of preventive or corrective maintenance
should be documented. In this way the system can be designed for minimum maintenance.
5 Principle of maintainability
This standard examines the maintainability and related design and use parameters and
discusses some of the activities necessary to achieve the required maintainability character-
istics and their relationship to the planning of maintenance.
Maintainability has a major impact on the cost of support and the availability of an equipment
and is concerned with characteristics of design, manufacture and installation which affect the
ability of an item to conform to specified requirements of use and of maintenance. This ability
is usually measured in both qualitative and quantitative terms.
NOTE The concepts described in this standard can be applied to a small product or to a major project and
therefore, as defined in IEC 60050(191):191-01-01:1990, “item” is used to denote any part, device, subsystem,
functional unit, equipment or system that can be individually considered.
The maintainability characteristics depend on the following:
a) the ability of the item to be retained in or restored to service (subject to the provision of
facilities for diagnosis and accessibility of parts, etc.), all conditions of use being taken
into account. The maintainability of an item is concerned with these matters but subject to
the restraints of b);
b) maintenance support, which is actually applied (personnel, training, stocks of spares,
facilities, manuals, etc.). The efficiency of the maintenance support system governs the
overall time to undertake the repair.
6 Maintainability activities in the life cycle
6.1 General
This standard essentially looks at the maintainability activities in the design and development
phase, but there are activities during the other phases of the life cycle of an item in
connection with maintainability and maintenance whose definition and achievement assist in
providing the required availability and ensuring a cost-effective system. These activities are
described below.
60706-2  IEC:2006 – 21 –
6.2 Concept and definition phase
6.2.1 General
The conditions of use and of maintenance of the item place constraints upon the maintenance
concept that have to be considered during the feasibility study and the prediction of life cycle
costs. The principal constraints fall into two areas, namely that of operations and resources,
and the main constituents of each are given in 6.2.2 and 6.2.3.
6.2.2 Operational conditions
During the concept and definition phase, the following factors need to be considered:
– operating needs and performance;
– customer requirements;
– environmental conditions affecting operation and maintenance;
– means of identifying maintenance needs, particularly failure detection and localization of
causes of failure (testability is described in more detail in IEC 60706-5);
– restrictions on access for maintenance purposes;
– the impact of human factors;
– equipment, software and hybrid item partitioning for maintenance purposes dictated by
location, level of repair and skill classification of the maintainer.
6.2.3 Resources
The detailed resources are not considered at this stage, as an initial assessment needs to be
made of the possible use of existing support resources, but the following factors do need to
be considered:
– existing or required organization, locality, personnel and training;
– resources already committed;
– flexibility in acquiring new resources.
See IEC 60300-3-12 and IEC 60300-3-14, which give further details on the provision of
resources for maintenance support.
6.2.4 Defining maintainability requirements
Maintainability requirements should take into account operational, reliability and safety
requirements as well as cost constraints. This should result in a quantitative and qualitative
maintainability specification statement considering the maintenance concept and other
requirements for the item. Guidance on the maintainability clauses in specifications and
contracts are given in Clause 7. Consideration should also be given during this phase to the
verification of the requirements as explained in IEC 60706-3.
6.3 Design and development phase
6.3.1 Satisfying maintainability requirements
An effective means of satisfying the maintainability requirement is to carry out a maintain-
ability programme, designed as a logical part of the whole engineering programme. Guidance
for a comprehensive maintainability programme is given in IEC 60300-3-10.

60706-2  IEC:2006 – 23 –
6.3.2 Providing maintenance support planning data
Maintenance support planning shall be carried out in step with the development of an item to
ensure that the maintenance support is available when the item is put into use. The main
elements to be included in the maintenance support plan are as follows:
– procedures for maintaining the item (including major overhaul or software upgrades);
– the initial provisioning of spares, facilities, test equipment and tools;
– training and availability of maintenance personnel;
– technical manuals, etc.;
– testability;
– maintenance data collection system.
The plan should be consistent with the maintenance concept and needs to be updated
regularly.
A system for recording the analysis and feedback of data should also be instituted.
Recommended procedures are given in IEC 60706-3.
6.4 Manufacture and installation phase
The important maintainability activity in the phases following design and development, and
leading up to the operational use of an item, is verification that the inherent maintainability
designed into it has been achieved. This is a progressive activity, the extent of which depends
on the nature and complexity of the item, and involves repairs and maintenance, and
maintenance test tasks, carried out initially on prototype equipment, followed by early
production items, to ensure that they have met their maintainability targets. Further guidance
on verification and maintenance data collection is given in IEC 60706-3.
6.5 Operation and maintenance phases
After installation or deployment, preventive and corrective maintenance are carried out as
required. The important associated maintainability activities are the collection, analysis and
feedback of maintenance data. These data enable the following:
– the efficiency of the maintenance activities to be assessed;
– improvement of the design which may lead to the modification of the item;
– decisions to be made on the viability of maintenance and the possible need to renew the
item, including items with pre-defined lives.
6.6 Disposal phase
The decision to dispose of a product is governed partly by its ability to continue to function
satisfactorily, its level of reliability and maintainability and its operational cost. These factors
depend on the continued provision of spare parts and support and the availability of
replacement equipment.
The safe environmental disposal of an item is becoming increasingly important and may be
governed by statutory regulations.

60706-2  IEC:2006 – 25 –
7 Specification of maintainability requirements
7.1 Statement of maintainability requirements
Maintainability should be specified in such a way that the designer has a clear understanding
of the need for maintenance and the manner in which the item is to be supported. This may
be reflected in a statement that defines a requirement that can be enforced in a contract.
However, not all maintainability statements will be included in a contract, for example when a
new product is developed in-house, maintainability requirements or goals may be based on
company policy and anticipated use environment. In any case, it is essential that the
objectives are clearly specified and can be verified.
NOTE In this standard, the term “requirement” is used to denote the stated aim of the writer and whether or not it
is enforceable will be decided according to the local contractual situation.
The maintainability requirements in a specification may contain either quantitative or
qualitative requirements, or both. The methods for verifying that the requirements have been
satisfied should be stated, as should the existence of any constraints that might affect the
maintainability characteristics of the item.
There is a progressive link between requirement, specification and contract as follows:
– the requirement is the initial statement of performance characteristics produced by a
customer to which a potential supplier may submit a bid. It can also be put out from within
an organization as a result of market research on a future product;
– the specification is the proposed performance characteristics of the item that are expected
to respond to the requirement;
– if the specification of the proposed item is accepted, the agreed performance
characteristics can be written into a contract and become the agreed requirement. The
maintainability requirements are part of the overall specification and this clause details the
points that may be included.
A complete statement of maintainability requirements covers the following four broad areas:
– maintainability characteristics to be achieved by the item design;
– constraints to be placed on the item deployment which will affects its maintenance;
– maintainability programme requirements to be accomplished by the supplier to assure that
the delivered item has the required maintainability characteristics;
– provision of maintenance support planning.
The maintainability specification shall detail the maintainability requirements and the method
to be followed to achieve them.
The specification shall be stated in terms of maintainability requirements, some of which
should be specified as essential and others as desirable. The requirements should be given in
measurable terms that may be either quantitative or qualitative, and they should be verifiable
at later stages in accordance with prescribed procedures.
A maintainability specification typically covers requirements for the achievement of
maintainability at the operational level. However, since maintainability as an item character-
istic affects maintenance and support costs, and may also affect maintenance times at
different maintenance levels, statements should be included in the specification covering
achievements needed at all levels affected by the maintenance concept.

60706-2  IEC:2006 – 27 –
7.2 Maintainability characteristics
7.2.1 Quantitative maintainability characteristics
The required quantitative maintainability characteristics normally define the time that an item
is in a non-operable (down) state due to being under maintenance, and it is normally a
requirement that this time is kept to a minimum. There are a number of criteria that can be
used to state the required characteristics related to time to undertake the repair, a selection of
which are given in Table 1. The difference between them is that they express different
priorities between related item properties and that they allow for flexibility concerning trade-
offs to be made later in the programme. It is important that such factors are considered before
a specific requirement is included in the specification. Limits may also need to be specified for
the preventive maintenance tasks.
Table 1 – Examples of quantitative maintainability characteristics
Term Statistical Verification method
characteristic
Active maintenance time Mean, median or Design evaluation, demonstration or operational
a
maximum evaluation
Active corrective maintenance Mean, median or Design evaluation, demonstration or operational
a
time maximum evaluation
Active preventive maintenance Mean, median or Design evaluation, demonstration or operational
a
times maximum evaluation
Access time Value Design evaluation, operational evaluation
Number of maintenance hours Mean Design evaluation, operational evaluation
b
per operating hour
Number of appropriately skilled Mean, maximum or Design evaluation, operational evaluation
personnel per maintenance minimum

action
a
The maximum value shall be associated with a percentile – a commonly used value is 95 %.
b
Other time bases may be selected as appropriate, e.g. day, month, year.

The active maintenance time is often used to specify maintainability and includes the
following sub-elements:
– diagnosis (failure detection, fault detection and isolation, localization of cause, etc.);
– technical delays (typical technical delays include setting time, cooling, interpretation and
application of information, interpretation of displays, read out);
– restoration (disassembly, insert software patch, interchange, modify control code, re-
assembly, alignment, etc.);
– final check (testing procedures as necessary).
A variety of other maintainability characteristics may be specified for the item. Table 1
outlines some other types of characteristics associated with different classes of maintenance
time and verification methods.
The maintainability of an item may also include further detailed characteristics, such as
access, use of special tools and test equipment, and relationship with any existing
maintenance support.
60706-2  IEC:2006 – 29 –
Maintainability can be used as an indirect measure of availability, using the expression for
availability:
MTBF
Availability =
MTBF + MTTR
where
MTBF is the mean time between failures;
MTTR is the mean time to repair.
Assuming that the MTBF of an item is constant, the availability is a measure of the
maintainability in terms of the time to repair.
The relationship between the various elements of the overall maintenance down time is given
in IEC 60300-3-10:2001, Figure 2.
7.2.2 Qualitative maintainability characteristics
The required qualitative maintainability characteristics include the definition of product
functions, fault criteria, environmental and operational conditions and useful life of the item
during which the requirements have to be fulfilled. The qualitative characteristics are related
to the degree to which the item meets a specific maintenance and support policy. Where the
qualitative characteristics contains numerical values, it should be qualified by a statement of
the degree to which it should be met. This can be carried out by proportions of cases or
events, by confidence levels or by other probabilities. Otherwise, compliance shall be judged
by inspection or document review. Such policies can include statements as shown by the
following examples:
– repair shall be performed by personnel of stated skill level;
– repair shall be performed by replacement of items at specified levels;
– replaceable parts shall be plug-in units;
– maintenance shall be performed according to the user’s defined and established
procedures;
– failed part isolation shall be performed by built-in test equipment.
There is a range of other possible qualitative subjects which may be of concern, as listed
below:
– accessibility;
– maintenance skill level requirement;
– need for special tools and test equipment;
– need for adjustments;
– parts standardization;
– clear sub-system function identification;
− configuration control, fit and function;
– visual inspection access;
– built-in test equipment;
– properly marked test points;

60706-2  IEC:2006 – 31 –
– colour coding and labels, as appropriate;
– use of plug-in units;
– use of captive fasteners;
– use of handles on replaceable units;
– scope and range of technical manuals;
– risk of obsolescence of equipment;
– human factor limitations in the design of the item;
– safety of maintenance and operating personnel.
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