AEO Guide to Reliability, Availability and Maintainability
T MU AM 06002 GU
Guide
Version 1.0
Issued date: 27 July 2015
Important Warning This document is one of a set of standards developed solely and specifically for use on public transport assets which are vested in or owned, managed, controlled, commissioned or funded by the NSW Government, a NSW Government agency or a Transport Agency (as defined in the Asset Standards Authority Charter). It is not suitable for any other purpose. You must not use or adapt it or rely upon it in any way unless you are authorised in writing to do so by a relevant NSW Government agency. If this document forms part of a contract with, or is a condition of approval by a NSW Government agency, use of the document is subject to the terms of the contract or approval. This document may not be current. Current standards are available for download from the Asset Standards Authority website at www.asa.transport.nsw.gov.au. © State of NSW through Transport for NSW
Standard governance
© State of NSW through Transport for NSW
T MU AM 06002 GU AEO Guide to Reliability, Availability and Maintainability
Version 1.0 Issued date: 27 July 2015
Owner: Manager Systems Engineering Process, Asset Standards Authority
Authoriser: Principal Manager Authorisation and Audit, Asset Standards Authority
Approver: Director, Asset Standards Authority on behalf of the ASA Configuration Control Board
Document history
Version Summary of Changes
1.0 First issue.
For queries regarding this document, please email the ASA at [email protected] or visit www.asa.transport.nsw.gov.au
T MU AM 06002 GU AEO Guide to Reliability, Availability and Maintainability
Version 1.0 Issued date: 27 July 2015
Preface
The Asset Standards Authority (ASA) is an independent unit within Transport for NSW (TfNSW)
and is the network design and standards authority for defined NSW transport assets.
The ASA is responsible for developing engineering governance frameworks to support industry
delivery in the assurance of design, safety, integrity, construction, and commissioning of
transport assets for the whole asset life cycle. In order to achieve this, the ASA effectively
discharges obligations as the authority for various technical, process, and planning matters
across the asset life cycle.
The ASA collaborates with industry using stakeholder engagement activities to assist in
achieving its mission. These activities help align the ASA to broader government expectations
of making it clearer, simpler, and more attractive to do business within the NSW transport
industry, allowing the supply chain to deliver safe, efficient, and competent transport services.
The ASA develops, maintains, controls, and publishes a suite of standards and other
documentation for transport assets of TfNSW. Further, the ASA ensures that these standards
are performance-based to create opportunities for innovation and improve access to a broader
competitive supply chain.
This AEO Guide to Reliability, Availability and Maintainability has been developed on the
technical processes of ISO/IEC 15288:2008 by the ASA; reviewed by a consultative group
containing members from TfNSW stakeholder groups and approved by the ASA.
This guide aims to provide supplier organisations with guidance in managing engineering
activities involving systems that are required to be reliable, available and maintainable.
This guide has been approved by the ASA Configuration Control Board and is the first issue.
© State of NSW through Transport for NSW Page 3 of 36
Table of contents
T MU AM 06002 GU AEO Guide to Reliability, Availability and Maintainability
Version 1.0 Issued date: 27 July 2015
1. Introduction.............................................................................................................................................. 5
2. Purpose .................................................................................................................................................... 5
2.1. Scope ..................................................................................................................................................... 5
2.2. Application ............................................................................................................................................. 6
3. Reference documents ............................................................................................................................. 6
4. Terms and definitions ............................................................................................................................. 8
5. Reliability, availability, maintainability management ........................................................................ 10
5.1. Plan reliability, availability and maintainability management activities ................................................ 12
5.2. Definition of system boundaries and assumptions .............................................................................. 13
5.3. Identification of reliability, availability and maintainability requirements .............................................. 14
5.4. Allocation of reliability, availability and maintainability requirements .................................................. 14
5.5. Development of reliability, availability and maintainability acceptance criteria ................................... 15
5.6. Reliability, availability and maintainability analysis and modelling ...................................................... 15
5.7. Validation of reliability, availability and maintainability requirements .................................................. 16
5.8. Reliability, availability and maintainability deliverables ....................................................................... 17
6. Reliability, availability and maintainability tools and techniques .................................................... 17
6.1. Reliability block diagram analysis ........................................................................................................ 18
6.2. Failure mode, effects and criticality analysis ....................................................................................... 18
6.3. Fault tree analysis ................................................................................................................................ 19
6.4. Human reliability analysis .................................................................................................................... 20
6.5. Maintenance requirements analysis .................................................................................................... 22
6.6. Failure recording analysis and corrective action system ..................................................................... 23
Appendix A Examples of reliability block diagrams ........................................................................... 26
A.1. RBD - Station public announcement ................................................................................................... 26
A.2. RBD - Blue light emergency station ..................................................................................................... 27
Appendix B Examples of FMECA table - Bogie assembly .................................................................. 28
Appendix C Examples of fault tree analysis ........................................................................................ 29
C.1. Fault tree – Failure of electrical interlocking system ........................................................................... 29
C.2. Fault tree - Exceed safe speed (ETCS) ............................................................................................... 30
Appendix D Examples of human error analysis .................................................................................. 31
D.1. Human error analysis - Ticketing system ............................................................................................ 31
D.2. Human error analysis – Doors release system.................................................................................... 32
Appendix E Example of maintenance requirements analysis - Station escalator ........................... 33
Appendix F Example of FRACAS incident report – CPU motherboard ................................................ 36
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1. Introduction
An Authorised Engineering Organisation (AEO) engaged by TfNSW to undertake engineering
activities is required to have reliability, availability and maintainability (RAM) management
arrangements in place that are relevant to the engineering services or products that the AEO
provides to TfNSW. These arrangements should enable the planning, execution, and reporting
of all RAM management activities for a system and documented in a RAM management plan
and related progress report(s).
The T MU MD 00009 ST AEO Authorisation Requirements and T MU AM 06006 ST Systems
Engineering standard state mandatory requirements for RAM. This document provides
guidance on complying with the requirements stated in these standards.
This guide further elaborates the guidance described in TS 10504 AEO Guide to Engineering
Management.
AEOs should ensure that RAM management documentation meets the level required for the
complexity of engineering services provided and incorporate RAMS requirements in the design
and development of systems they are contracted to deliver.
2. Purpose
This document is intended to provide guidance to AEOs applying RAM management during
engineering specification and asset life cycle stages and activities involving systems that are
required to operate dependably.
This ensures that AEOs are able to demonstrate sufficient control over RAM-related risks. This
guidance is of particular relevance to suppliers who provide reliability-critical or safety-critical
engineering specification and design, in addition to systems engineering, integration and
maintenance services.
2.1. Scope
This document provides guidance to AEOs for reliability, availability and maintainability
management related, in particular, to the system specification, design and maintenance
services. It also provides guidance on RAM management principles, methods, techniques and
processes used to analyse and deliver RAM requirements from stakeholders including
operational, maintenance and interfacing targets. AEOs are assumed to have business-level
policies addressing quality, performance and safety.
For this guide, the term reliability, availability, maintainability and safety (RAMS) is used to
define an integrated management approach. However, this guide is limited to RAM and not the
safety element of RAMS management, as safety assurance is addressed in TS 20001 System
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Safety Standard for New or Altered Assets. Refer to this document for guidance on safety
management.
The specific evidence required to demonstrate RAM management processes will depend on the
scope and nature of the work. For that reason, this document does not outline the evidence
required to be an AEO, rather it provides an outline of the processes that AEOs need to
demonstrate.
2.2. Application
This document applies to the member Transport agencies and AEOs, and applies specifically to
the management of system and element level reliability, availability and maintainability for new
or altered NSW transport assets.
The level of application of RAM management principles should be scalable and tailored
according to the degree to which novelty or complexity is employed, the use of unique or
non-standard configurations and the associated level of safety risk.
The application of RAM analysis in support of design may be negligible or zero for some
projects where type approved products are used in standard, repeatable system configurations.
This should be reflected in contractual requirements to avoid unnecessary and excessive effort,
resources, time and cost.
The need for and application of RAM management has different meaning to different disciplines.
The impact of RAM management on planning and acquisition of new or altered systems and the
specific disciplines that support the system design should be understood.
T MU AM 06006 GU Systems Engineering guide provides guidance on the level of RAM
management activities required for engineering disciplines and identifies a range of typical rail
engineering projects and the level of RAMS to be applied.
3. Reference documents
The following documents are either cited in the text or may provide further information. For
dated references, only the cited edition applies. For undated references, the latest edition of the
referenced document applies.
International standards
EN 50126:1999 Railway applications - The specification and demonstration of Reliability,
Availability, Maintainability and Safety (RAMS)
EN 50128:2011 (Railway applications - Software for railway control and protection)
EN 60706 Maintainability of Equipment, Testability and diagnostic testing
ISO/IEC 15288:2008 Systems and software engineering - System life cycle processes
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ISO/IEC 26702:2007 - Application and Management of the Systems Engineering Process
(Formally IEEE Std 1220-2005)
IEC/TR 62380:2004 Reliability data handbook - Universal model for reliability prediction of
electronics components, PCBs and equipment
Australian standards
AS ISO 55001:2014 Asset management - Management systems - Requirements
AS IEC 60300.2.2005 Dependability management - Part 2: Guidance for dependability
programme management
AS IEC 60812:2008 Analysis techniques for system reliability - Procedure for failure mode and
effects analysis (FMEA)
AS IEC 61025-2008 Fault tree analysis (FTA)
AS IEC 61078-2008 Analysis techniques for system reliability - Reliability block diagram and
Boolean methods
AS IEC 62508-2011 Guidance on human aspects of dependability
Transport for NSW standards
T MU MD 00008 GU AEO Guide to Authorisation
T MU MD 00009 ST AEO Authorisation Requirements
T MU AM 01003 ST Development of Technical Maintenance Plans
T MU AM 01003 F1 Blank FMECA Sheet
T MU AM 06001 GU AEO Guide to Systems Architectural Design
T MU AM 06007 GU Guide to Requirements Definition and Analysis
T MU AM 01010 ST Framework for developing an Asset Spares Assessment and Strategy
T MU HF 00001 GU AEO Guide to Human Factors Integration
TS 10504 AEO Guide to Engineering Management
TS 10506 AEO Guide to Verification and Validation
TS 20001 System Safety Standard for New or Altered Assets
T MU AM 01002 MA Maintenance Requirements Analysis Manual
T MU AM 06006 ST Systems Engineering (standard)
T MU AM 06006 GU System Engineering (guide)
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Other references
MIL-HDBK-781A, Reliability Test Methods, Plans, and Environments for Engineering
Development, Qualification and Production
MIL-HDBK-217F, Notice 2, Reliability Prediction of Electronic Equipment
MIL-STD-2155(AS), Failure Reporting, Analysis and Corrective Action System
Williams, J.C., HEART – A proposed method for achieving high reliability in process operation
by means of human factors engineering technology in Proceedings of a Symposium on the
Achievement of Reliability in Operating Plant, Safety and Reliability Society,1985, NEC,
Birmingham
Swain, A.D. and Guttmann, H.E., Handbook of Human Reliability Analysis with Emphasis on
Nuclear Power Plant Applications. 1983, NUREG/CR-1278, USNRC
Shappell, S.A. and Wiegmann, D.A., The Human Factors Analysis and Classification System—
HFACS, February 2000, DOT/FAA/AM-00/7
Stanton, N. A., Salmon P. M. et al, Human Factors Methods A practical guide for Engineering
and Design, 2nd Edition, 2013, Ashgate, Aldershot, ISBN 978-1-4094-5754-1
ETCS Application Level 1 - Safety Analysis Part 1 - Functional Fault Tree, SUBSET-088-1 Part
1, Issue 2.3.0
Railtrack EE &CS Report, Infrastructure Risk Modelling Geographical Interlocking,
RT/S&S/IRM_FTA/11 Issue 1 January 1998
4. Terms and definitions
AEO Authorised Engineering Organisation (as defined in ASA Charter) a legal entity (which
may include a Transport Agency as applicable) to whom the ASA has issued an ASA
Authorisation
ASA Asset Standards Authority
ASA Authorisation means an authorisation issued by the ASA to a legal entity (which may
include a Transport Agency as applicable) which verifies that it has the relevant systems in
place to carry out the class of Asset life cycle work specified in the authorisation, subject to any
conditions of the authorisation. The issue of ASA Authorisation confers the status of 'authorised
engineering organisation' or AEO on the entity.
assurance a positive declaration intended to give confidence
authorisation the conferring of authority, by means of an official instruction and supported by
assessment and audit
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availability the measure of the percentage of time that an item or system is available to perform
its designated function
BRS business requirements specification
compliance the state or fact of according with, or meeting, rules or standards
ETCS European train control system
failure the inability of a system or asset to perform its intended function or satisfy some
predetermined conditional attribute (for example, rail head profile or gap size)
fault tree logic diagram showing the faults of sub items, external events, or combinations
thereof, which cause a predefined, undesired event
fault tree analysis deductive analysis using fault trees
FMECA failure mode, effects and criticality analysis
FRACAS failure recording analysis and corrective action system
HEART human error assessment and reduction technique
HFACS human factors analysis and classification system
HRA human reliability analysis
MRA maintenance requirements analysis
maintainability (as defined in IEC 60050-191)the probability that a given active 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
MTBF Mean Time Between Failures
MTTR Mean Time to Repair
RAMS reliability, availability, maintainability and safety
RBD reliability block diagram a diagrammatic method for demonstrating the contribution of
component reliability to the success or failure of a complex system
RCIL reliability critical items list
reliability the probability that a specified item will perform a specified function, within a defined
environment, for a specified length of time
responsible a duty or obligation to satisfactorily perform or complete a task (assigned by
someone, or created by one's own promise or circumstances) that one must fulfil, and which
has a consequent penalty for failure. Responsibility can be delegated
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review a method to provide assurance by a competent person that an engineering output
complies with relevant standards and specific requirements is safe and fit for purpose
SME subject matter expert a person assessed or recognised as having the highest level of
competence (including knowledge, skills and practical experience) in a particular field or
discipline
SRS system requirement specification
supplier a supplier of services or products. Defined as an 'applicant' until such time as it has
been granted AEO status, after which it is referred to as an AEO.
system safety the concurrent application of a systems based approach to safety engineering
and of a risk management strategy covering the identification and analysis of hazards and the
elimination, control or management of those hazards throughout the life cycle of a system or
asset
Transport Agencies Transport for NSW (and each of its divisions), Rail Corporation NSW,
Sydney Trains and NSW Trains
TfNSW Transport for New South Wales
THERP technique for human error rate prediction
Transport Assets those assets listed in Schedule 1 (of ASA Charter) which are vested in or
owned, managed, controlled, commissioned or funded by the NSW Government, a NSW
Government agency or Transport agency
5. Reliability, availability, maintainability management
T MU MD 00009 ST states the following requirement:
"The Authorised Engineering Organisation shall demonstrate that it has reliability,
availability and maintainability (RAM) management arrangements in place, relevant to
the engineering services or products provided".
T MU AM 06006 ST states the following requirement:
"A project shall implement management arrangements that define the reliability,
availability, maintainability and safety (RAMS) process, responsibilities, structure, tools
and deliverables"
The introduction of new or altered assets results in complexity and RAM implications.
Implementation decisions should be made based on trade-offs between implementation costs
and the subsequent operation and maintenance.
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Consideration should be given to the total impact on the existing network, existing maintenance
activities such as safety working and additional possessions.
The introduction of new assets that simplify the network should generate RAM improvements.
However the introduction of new assets that do not simplify the network may not generate RAM
improvements.
Application of reliability, availability and maintainability (RAM) engineering is required to ensure
optimum system effectiveness, safety and availability. RAM engineering is a whole of system
life cycle philosophy that is applied during plan, acquire, operate/maintain, and dispose stages.
RAM management activities which include planning and producing deliverables should be
carried out by suitably qualified and experienced individuals. Deliverables for RAM management
should be appropriate and sufficient such as to provide assurance to stakeholders that the
system can satisfy the high level performance targets as required. TfNSW should provide the
performance targets. For example, the availability performance target of 92% on-time running of
trains.
The following RAM activities should be undertaken but not limited to:
plan the RAM management activities
define system boundaries and assumptions for RAM analysis
identify the system RAM requirements
allocate the requirements to elements
develop the RAM acceptance criteria
undertake RAM analysis and modelling
validate the RAM requirements
System failure recording and analysis is undertaken using a range of tools and processes.
These include, but are not limited to the following:
failure mode, effects and criticality analysis (FMECA)
reliability block diagrams
fault tree analysis
failure recording analysis and corrective action system (FRACAS)
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5.1. Plan reliability, availability and maintainability management activities
T MU AM 06006 ST states the following requirements:
“A project shall consider RAMS performance and how it relates to operational
performance for novel systems early in the system life cycle, starting with
development of the operational concept definition and maintenance concept definition”
“A project shall consider sustainable operation and maintenance of the new or altered
system over the full system life cycle”
At the beginning of the project, before undertaking any asset life cycle stages and activities
related work, AEOs should prepare a RAM management plan. Depending on the level of
complexity the plan may be combined with other asset related plans to demonstrate how the
system RAM requirements will be achieved.
The RAM management plan should focus on managing RAM across the asset life cycle stages
and the activities rules and principles that are required to be adopted including the following:
reliability
o use of proven systems and equipment (assurance figures should be obtained)
o use of systems that are applicable to the conditions (systems proven in other countries
may not be suitable to NSW)
o human factors
o fault tolerance and graceful degradation
o the levels of redundancy designed into the system
availability
o maintenance scheduling
o service recovery
maintainability
o condition monitoring and diagnostics
o condition inspections
o obsolescence
o human factors
o resources
o access arrangements for maintenance
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o maintenance scheduling
o isolation for maintenance
o preventative maintenance
o corrective maintenance
o human factors considerations for maintenance
The RAM management plan should also include details on the roles and responsibilities
required within the organisation to achieve the RAM objectives.
Where there are proposed changes to an existing system the RAM management plan should
consider the resulting impact to the system RAM from these changes. The RAM management
plan should, where practical, include an assessment of the existing system RAM and the
changes to the RAM resulting from the new or altered assets.
An example of an impact to the reliability is the addition of a platform display to an existing light
rail system. The light rail operating contract specifies a maximum of three isolations of the line
per year. The platform display system needs to have reliability to work within this limitation.
An example of impact to the availability is if the relocation of a maintenance depots from
multiple existing locations to a new central location. The relocation of the maintenance depots
results in additional travelling distances from the central depot to faults and an increase to the
maintenance response time.
An example of impact to the maintainability is the addition of two extra railway running lines to
an existing double running line system. These two additional running lines alter the
maintainability of the combined services route and sub-stations adjacent to the original two
lines. These assets transition from a safe place location to a danger zone location and
additional safety procedures will be required to maintain these assets.
5.2. Definition of system boundaries and assumptions
System and element boundaries should be defined clearly and by means of defined system
architecture, before starting any RAM activities.
Assumptions may be made as a result of incomplete information in instances where programs
are large or complex. As system definition progresses, these assumptions should be clarified as
either statement of fact, or eliminated within the system design process. Clarification of these
assumptions should be sort with the asset owner (client representative).
The system architecture may need to change, based on the inability to satisfy system RAM
requirements.
Refer to T MU AM 06001 GU AEO Guide to Systems Architectural Design for more information.
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5.3. Identification of reliability, availability and maintainability requirements
T MU AM 06002 GU AEO Guide to Reliability, Availability and Maintainability
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The asset owner (client representative) should provide, early in the asset lifecycle, the high level
system RAM objectives.
RAM requirements captured from the stakeholders should be well-defined, demonstrable,
include explicit targets and meaningful to allow efficient RAM activities to be conducted. RAM
requirements should be considered in the context of their implementation cost. If the RAM
targets are very exacting then the resulting implementation cost may be very high. The RAM
requirement capture should start with the business requirement specification (BRS) and be
further refined in the system requirement specification (SRS) development process. Any
requirements which fall outside these criteria should be challenged and clarified as necessary.
Refer to T MU AM 06007 GU Guide to Requirements Definition and Analysis for more
information.
5.4. Allocation of reliability, availability and maintainability requirements
RAM requirements allocation assures that the high level BRS RAM targets are allocated
appropriately at system and element levels. Models based on reliability block diagrams and
other modelling techniques should be employed in the allocation process for novel, highly
complex systems. The allocations should be used as an aid to achieving the RAM objectives.
These system and element level RAM targets should then be converted into RAM requirements.
To ensure realistic allocation, system and element RAM requirements should be compared to
empirical data for identical or similar systems whenever possible. The empirical data should be
validated for its relevance considering factors such as the modes of operation, the operating
environment and any fine-tuning or adjustments that have been used. If allocated values are not
achievable, design options analysis across systems and elements should be performed to
reallocate system RAM requirements. The process of allocation, comparison with empirical
data, trade-offs and iteration as required should result in system and element RAM
requirements being defined.
The allocation of a RAM target to each system and element should be specific, measurable and
attainable, taking into account the criticality and risks involved in the design, development and
installation.
Systems and elements that are critical to performance should have RAM targets set higher than
other non-critical systems, based on the system level reliability or redundancy employed. When
allocating RAM targets, the number and complexity of the system interfaces and the extent to
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which the system will be affected by external factors including the operating environment needs
to be considered.
5.5. Development of reliability, availability and maintainability acceptance criteria
The acceptance criteria for RAM requirements should be agreed between the stakeholders
including the asset owner (client representative) and system developer.
These stakeholders may include representatives from the transport agencies.
This should include, but not limited to, the RAM validation principles to be applied and the tests
and analysis to be carried out for the validation. Acceptance criteria should be agreed and
documented through the requirements allocation process starting with the BRS and then the
SRS. Consideration should be given to the cost of implementing the acceptance criteria.
5.6. Reliability, availability and maintainability analysis and modelling
T MU AM 06006 ST states the following requirement:
"A project shall use RAMS modelling to appropriately support option selection and
development and preliminary system design, to ensure that the new or altered system
will meet the stated operational capability and provide value for money over the
designed system lifetime"
During the plan and acquire stages of a project, reliability predictions should be used to assess
whether the allocated RAM requirements are achievable. An iterative process of comparing
predictions with allocations which combined with trade-off studies, eventually results in an
efficient design that achieves whole of life performance targets.
Predictions combine lower level component or unit level reliability data through reliability
modelling and the operating and environmental conditions to estimate the integrated system
reliability. The validity of the reliability predictions is highly dependent upon the quality of
reliability data and assumptions made.
Whenever possible, reliability predictions should be based on data from similar components or
equipment already in use in service, in similar operational environments. For electronic
equipment, parts count prediction methods based on MIL-HDBK-217F Notice 2 can be used to
obtain reliability predictions. Where this is not possible, reliability data may be extrapolated from
tests or trials conducted by the supplier or manufacturer. In all cases the sources of the data
should be cited to maintain an audit trail. Suppliers of original equipment and systems should
provide evidence that they satisfy all RAM requirements and that they are suitable for the
intended application.
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Reliability prediction should use reliability modelling where practicable for novel, high complexity
systems, such as a reliability block diagram, fault tree or a computerised simulation model, to
describe the reliability behaviour of the system and reliability data of the constituent elements.
RAM predictions are performed predominantly for the following purposes:
reliability
o to evaluate reliability performance against target risk of failure
o to identify weaknesses in a design, including single point failures
o to provide basis for a testing program
o to predict maintenance effort and cost
availability
o to evaluate outage times and service disruptions against economic, community and
quality criteria
o to identify critical subsystems and components
o to determine the need for redundant or stand-by equipment
maintainability
o to determine the most effective maintenance strategy
o to optimise maintenance facilities, diagnostic and training tools, spares holdings and
manning levels
o to assess need for condition monitoring
Reliability block diagrams (RBD) and fault tree analysis (FTA) are systematic top-down reliability
modelling and analysis techniques, and are usually best applied when introducing novel, highly
complex new or altered systems.
In addition to RAM modelling, complimentary analysis techniques should be used during design
to concentrate on areas which are critical to the system reliability, such as failure mode, effects,
and criticality analysis (FMECA).
5.7. Validation of reliability, availability and maintainability requirements
Validation should include details of the validation tasks and relevant results against the RAM
acceptance criteria. Any limitations and constraints applying to the system should also be noted.
There are numerous sources of international good practice in reliability and maintainability
validation. These include MIL-HDBK 781, EN 60300-3 and EN 60706.
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A RAM report including results from the analysis and verification and validation activities should
be prepared and then issued to stakeholders. Refer to TS 10506 AEO Guide to Verification and
Validation for more information. The RAM report should clearly display all verification and
validation failures against RAM acceptance criteria. Corrective action should then be
undertaken to rectify these failures. Validation and verification activities should be repeated and
the RAM report re-issued.
5.8. Reliability, availability and maintainability deliverables
The following deliverables should be produced during the RAM process:
RAM management plan including the asset life cycle stages
BRS RAM requirements with their acceptance criteria
SRS RAM requirements with their acceptance criteria
element level RAM requirements with their acceptance criteria
RAM analysis and modelling with their data
RAM report including results from the analysis, modelling, verification and validation
activities
6. Reliability, availability and maintainability tools and techniques
Careful consideration should be given to the selection of the appropriate RAM tools and
techniques used to provide RAM results. This consideration involves a critical decision as to
whether a simple calculation or a comparison with an existing system is sufficient or whether
RAM tools and techniques are required.
These tools and techniques may provide different RAM results as the system definition
progresses. These progressive RAM results should be recorded in the RAM report during the
asset life cycle stages.
Different asset types may have different approaches and tools for RAM modelling and analysis.
Communications, signalling and electrical designers may use reliability block diagram (RBD)
analysis, failure mode, effects, and criticality analysis (FMECA) or fault tree analysis (FTA)
tools, whereas bridge and structural designers may use finite element analysis (FEA) tools.
The reliability, availability and maintainability tools and techniques are explained in Section 6.1
through to Section 6.6.
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6.1. Reliability block diagram analysis
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AS IEC 61078 describes reliability block diagrams (RBD) as a diagrammatic analysis method for
demonstrating the contribution of component reliability to the success or failure of a complex
system.
A reliability block diagram is drawn as a series of blocks connected in parallel or series
configuration with each block representing a component of the system with an associated failure
rate. Parallel paths are redundant, meaning that all of the parallel paths are failed for the parallel
network to fail. By contrast, any failure along a serial path causes the entire serial path to fail.
Reliability block diagrams are used to calculate the reliability of each element and the
contributory effect on the reliability of the system. This assists in the identification of single
points of failure in the system.
Examples of where a reliability block diagram would be used are for the development of a
station announcement system and a blue light emergency station provided in Appendix A.
6.2. Failure mode, effects and criticality analysis
AS IEC 60812 describes failure mode, effects and criticality analysis (FMECA) as a 'bottom up'
analysis method that is used to understand failure modes and their escalation effect, both at a
local and a system wide level. This method requires the system design to be well defined down
to unit level.
Each system is broken down into its elements, usually down to line replaceable unit level where
each element is then analysed uniquely to identify functional failures and relevant modes of
failure, and their escalated effect on the next higher level of the system.
This process is employed to identify those elements of a system which have a significant impact
on system reliability, availability and safety. This analysis is further used to promote mitigation
measures leading to improved system reliability and availability.
FMECA is typically used for high level analysis of system reliability through the following
process:
identification of failure modes and consequences, and facilitation of design modifications
assessment of failure causation, performance limits and vulnerability issues
classification of failure modes relative to the severity of their effects
An output of the FMECA should be a reliability critical items list (RCIL). This is a list of items
which have at least one failure mode classified as critical according to its criticality analysis.
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Consideration should also be given to common-mode failure where an event causes multiple
systems to fail. For example an explosion in a room causes both transformers in the room to fail
at the same time.
An example of where a FMECA would be used is for the development of a bogie system for a
train provided in Appendix B.
Refer to T MU AM 01003 F1 Blank FMECA Sheet for further details.
6.3. Fault tree analysis
Fault tree analysis should be used for highly complex or safety or reliability critical systems.
Fault tree analysis should be done during the initial stage of the project and updated as more
details become available during subsequent stages of the project.
AS IEC 61025 describes fault tree analysis as a top down deductive failure analysis. An
undesired state of a system is analysed using Boolean logic to combine a series of lower-level
events. This analysis method is used to determine the probability of a safety accident or a
particular system level (functional) failure.
The basic symbols used in fault tree analysis are grouped as events, gates, and transfer
symbols. Event symbols are used for primary events and intermediate events. Primary events
are not further developed on the fault tree. Intermediate events are found at the output of a
gate. Events in a fault tree are associated with statistical probabilities. Gate symbols describe
the relationship between input and output events. The gate symbols are derived from Boolean
logic symbols. Transfer symbols are used to connect the inputs and outputs of related fault
trees, such as the fault tree of a subsystem to its system.
Fault tree analysis incorporates the following phases:
definition of the undesired system top event to analyse
obtaining an understanding of the system functional breakdown
construction of the Boolean fault tree from top event down to base events
assignment of failure rates to the base events
evaluation of the fault tree
control of the hazards identified
Examples of where fault tree analysis would be used are the risk of a rail vehicle collision and
exceed safe speed (ETCS). The contributory factors that lead to these system top events are
provided in Appendix C.
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6.4. Human reliability analysis
T MU AM 06006 ST states the following requirement:
"A project shall consider human reliability factors as part of the overall reliability of the
system"
The purpose of conducting human reliability analysis (HRA) is to ensure that the actual
performance of the system is in line with its designed requirements. Humans are an integral part
of designed systems, playing important roles in operation, accidents prevention and
maintenance activities.
Operators and maintainers should be trained and competent; however ‘trained and competent
people’ is not a way of preventing human error. Human error is a normal part of human
performance, and should be appropriately assessed to create resilient systems. Early,
appropriate HRA is essential to ensure the exploration of the appropriate hierarchy of controls.
Delayed or ineffective assessments tend to create dependencies on administrative risk control
which can create latent system weaknesses.
Therefore, analysing and predicting the reliability of a system without assessing human
reliability may result in an over estimation of system performance.
Although there are many ways in which a human can positively impact on system performance,
the focus within a RAM assessment is usually to identify the following:
human errors that may impact on the RAM of the system
mitigation measures to reduce likelihood of human errors or to reduce impact of these
errors on the system
These measures can relate to the design of the equipment or the task, or may warrant
additional redundancy or diversity to be incorporated within the overall system design.
In order to be able to identify the errors that can be made and what their likely effect on the
performance of the system would be it is necessary to identify but not limited to the following:
the tasks that are required to be carried out by operators and maintainers
the likely conditions under which those tasks will be performed
the potential errors that could be made
With many other aspects of the design in the early stages, information may be at a relatively
high level and should be used to identify those areas of the system where a more detailed
assessment is of most value.
There are a number of methods available for identifying human errors ranging from utilising past
experience through to the application of structured processes based on guidewords or
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checklists. Human error should be built into existing analysis techniques such as FMECA or
FTA.
In those cases where a quantitative assessment is required, techniques for human error rate
prediction may be employed for evaluating the probability of a human error occurring and
impacting on system performance. This should then be incorporated into the system models to
assess the impact on the overall system performance.
Techniques to evaluate the probability of human errors fall into the following three general
categories:
the use of screening data
the use of historical or subjective data
the use of human error databases
Examples of where a human reliability analysis would be used are for a ticketing system and a
door release system provided in Appendix D.
Refer to T MU HF 00001 GU AEO Guide to Human Factors Integration for more information on
HRA.
6.4.1. Screening data
A single screening value for human error within a system model may be used in the early
stages of an assessment. This enables an organisation to identify where the system is
particularly vulnerable to human error and to review the design in terms of the level of
redundancy or diversity that is currently built in, or to identify whether a more detailed
assessment may be required.
6.4.2. Historical or subjective data
Actual performance data, if available, may be used as estimation within reliability models. This
data is normally only available at the system level and does not specifically highlight the human
error contribution. However, it is estimated that approximately 70% - 90% of failures are due to
human error and so it is possible to factor the data in this way to obtain a more reliable
estimate.
Note: Manufacturer's data generally does not include human errors and so it will be
indicative of performance based on 100% reliability of people.
Alternatively, subjective data may be sought through consultation with users or their opinions
and may be used to modify existing data.
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6.4.3. Human error databases
A number of techniques are used for quantitative human error assessments where it is possible
to look up a generic human error probability and then modify it according to the specific task.
Commonly used examples include the following:
Human Error Assessment and Reduction Technique (HEART)
HEART method is based upon the principle that every time a task is performed there is a
possibility of failure and that the probability of failure is effected by one or more error
producing conditions to varying degrees. Error producing conditions include topics such as
training, poor procedures, poor system feedback and so on.
Factors which have a significant effect on performance are of greatest interest. These
conditions are applied to a ‘best-case-scenario’ estimate of the failure probability under
ideal conditions to then obtain a final error probability. By forcing consideration of the error
producing conditions potentially affecting a given procedure, the application of HEART also
enables the user to identify a range of potential improvements to system performance.
An example of where HEART would be used is the assessment of a critical maintenance
task.
Technique for Human Error Rate Prediction (THERP)
THERP models human error probabilities using an event tree approach, in a similar way to
an engineering risk assessment, but also considers performance shaping factors that may
influence these probabilities. The probabilities for the human reliability analysis event tree,
which is the primary tool for assessment, are nominally calculated from historic databases,
local data including simulated data or from accident reports. The resultant tree portrays a
step by step account of the stages involved in a task in a logical order. The technique is
described as a total human reliability assessment methodology as it simultaneously
manages a number of different activities including task analysis, error identification and
human error quantification.
6.5. Maintenance requirements analysis
Maintenance requirements analysis (MRA) is the inclusion of reliability, availability and safety
integrity as a part of the maintenance requirements of the system.
Maintenance requirements analysis applies reliability theory principles within a structured
process designed to identify effective maintenance and inspection tasks that would detect or
delay failures of equipment. This ensures that maintenance requirements are incorporated into
the design activities.
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The following elements are inherent in maintenance requirements analysis:
identify the maintenance item
Identify the items to be maintained at system, element, assembly, unit, component level as
part of the asset breakdown structure.
establish the function
Identify all functions associated with the maintenance item.
establish failure modes and effects
Identify and analyse all possible failures to or deviations from the specified functionality
associated with the maintenance item. Analyse their escalation effects from component
level to unit level to assembly level to subsystem level to system level.
recognise failure
Identify the means by which each failure is detected and communicated to the maintainer.
identify maintenance task options
Identify how each maintenance item should be repaired or replaced (both preventative and
corrective maintenance tasks).
establish maintenance task intervals
Identify a maintenance program which includes the schedule of inspection or replacement
for all maintenance items.
An example of where maintenance requirements analysis would be used is for the development
of a station escalator provided in Appendix E.
Refer to T MU AM 01003 ST Development of Technical Maintenance Plans and
T MU AM 01010 ST Framework for developing an Asset Spares Assessment and Strategy for
further details.
6.6. Failure recording analysis and corrective action system
A failure recording analysis and corrective action system (FRACAS) should be applied from that
point in the design cycle at which a version of the product or service approximating the final
operational version becomes available until the product or service is decommissioned.
The FRACAS is a closed loop process incorporating data reporting, collecting, recording,
analysing, investigating and timely corrective action for all failure incidents. The objective of the
system is to aid design, identify corrective action tasks and evaluate test results in order to
provide confidence in the results of the safety analysis activities in addition to the correct
operation of the safety features.
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The effectiveness of FRACAS is dependent upon accurate input data in the form of reports
which should document all the conditions relating to the incident.
Incident reviews should be undertaken to ensure that the impact on the safety and reliability
characteristics of the product or service are quickly assessed, with any corrective actions
requiring design changes, quickly approved.
The FRACAS process is outlined as follows and is illustrated in Figure 1:
an incident report is raised and recorded in a database
a data search is carried out for related events
the incident is reviewed - if the incident is a new hazard it is recorded as such in the hazard
log
information concerning the incident is communicated to those that need to know, in order to
control risk
corrective actions are recommended, as necessary
if no corrective action is required, the database is updated and the process ends
the corrective action is authorised and implemented then assessed for success
if the corrective action is unsuccessful, the incident is re-reviewed, corrective actions are
modified as required, details are updated in the database and the action returns for further
authorisation to proceed
if the corrective action is successful, the database is updated and the process ends
An example of where FRACAS would be used is the development of a CPU motherboard
provided in Appendix F.
© State of NSW through Transport for NSW Page 24 of 36
No
Incident raised and recorded
Search for related events
Review incident
Communicate information as necessary
Corrective action
necessary?
Authorise, implement and assess plan
Corrective action
successful?
Update
Yes
Yes
No
database
Figure 1 - FRACAS process
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Appendix A Examples of reliability block diagrams
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Figure 1 and Figure 2 provide examples of reliability block diagrams for station public announcement and blue light emergency station, respectively.
A.1. RBD - Station public announcement
Page
Loudspeakers
STM 64 Port P.MUX AMD II
Matrix Enhanced
MTBF=157.680 H
MTBF=183.960H
MTTR=2hours
MTTR=2hours
Network Fibre
MP50 Call Station
MTBF=163.549 H
MTTR=2hours
STM 64 Port
Matrix Enhanced
P.Mux AMD II
MTTR=2hours
MTBF=183.960H
MTBF=157.680 H
MTTR=2hours
MTBF=163.549 H
MTTR=2hours
Amplifier Module V400 Amplifier Mainframe
VIPET
P1 Ethernet Switch
PCAS Workstation
VIPA HOST VAR 4
Network Fibre
MTBF=600000H
MTTR=24h
MTBF=600000H
MTTR=24h
MTBF=21400 H
MTBF=121354 H
MTTR=2hours
MTBF=39800H MTBF=65000H
MTBF=48681 H MTBF=96400 H MTBF=215800 H MTBF=118600H
MTTR=4h MTTR=1h MTTR=4h
MTTR=4 hours MTTR=4 hours MTTR=4 hours MTTR=4 hours
Loudspeakers
MTBF=87600H
MTBF=87600H
MTTR=2hours
Service board
MTBF=621.960 H
MTTR=2hours
Service board
MTBF=621.960 H
MTTR=2hours
Matrix Enhanced
MTBF=157.680 H
MTTR=2hours
Matrix Enhanced
MTBF=157.680 H
MTTR=2hours
Switch OS6450-24
MTTR=2hours
MTBF=894251H
MTTR=2hours
Figure 2 - RBD station public announcement (sample fragment)
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A.2. RBD - Blue light emergency station
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Relays
MTBF=100,000 H MTBF=50,000 H MTBF=100,000 H MTBF= 100,000 H MTBF=50,000 H
Input Relay Push Button
Comms Module Output Relay Input Relay Alarm Module Push Button
Emergency
with Key Reset
MTBF= 50,000 H with Key Reset MTBF=600,000 H
Emergency Comms Module Output Relay Alarm Module
MTTR=4 hours MTTR=1 hour MTTR=1 hour MTTR=1 hour MTTR=1 hour Blue Light 240V AC Display UPS
MTBF=100,000 H MTBF=50,000 H MTBF=100,000 H MTBF= 100,000 H MTBF=50,000 H MTTR=3 hours MTTR= 3 hours
MTTR=4 hours MTTR=1 hour MTTR=1 hour MTTR=1 hour MTTR=1 hour
Figure 3 - RBD blue light emergency station (sample fragment)
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Appendix B Examples of FMECA table - Bogie assembly
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Table 1 provides an example of FMECA table for bogie assemble.
Table 1 - FMECA table (sample fragment)
ents
Analysts: Fred Person, Joe Smith Function General
1 Secure wheel bearings and wheel set
Item/Assembly Name: Bogie Assembly Drawing No: BOG-123 2 Maintain wheels to track gauge
Part No: GOB-457-631
Functional Description: Provides the interfacing and suspension of the train body to the track
3 Provide 1kN braking force per wheel set
4 Permit low friction axle rotation
MTBF (hrs) 100,000 Task Type P –Preventative, S-Surveillance, C - Corrective
Function Part Failure Mode
Cause of Failure
Local Effect % Failure Rate
Tasks Type Period Latitude Insp Comm
Secure wheel bearings and wheel set
Bogie frame
Wheel bearing unsecured
Bearing cradle cracked
Wheel bearing vibration
100 1/1000 Wheel bearing cradle inspection
S 6 month
Maintain wheels to track gauge
Wheel set
Wheel to track gauge lost
Axle cracks Wheel gauge mismatch to track gauge
100 1/5000 Wheel set gauge inspection
S 6 month
Provide 1kN braking force per wheel set
Brake assembl y
Reduced braking force
Brake pads worn beyond limits
Reduced braking on bogie set
100 1/5000 Brake pad thickness inspection
S 6 month
Permit low friction axle rotation
Wheel Bearing
Bearing friction increase
Metal fatigue & bearing seizure
Wheel bearing overheat
100 1/10000 Bearing inspection and replacement
C 3 month
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Appendix C Examples of fault tree analysis
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Figure 4 and Figure 5 provide examples of fault tree analysis for failure of electrical interlocking system and exceed safe speed, respectively.
C.1. Fault tree – Failure of electrical interlocking system
Figure 4 - Fault tree failure of electrical interlocking system (sample fragment from Railtrack EE&CS Report)
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C.2. Fault tree - Exceed safe speed (ETCS)
Figure 5 - Fault tree for exceeding safe speed (sample fragment from ETCS Application Level 1 - Functional Fault Tree)
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Appendix D Examples of human error analysis
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Table 2 and Table 3 provide examples of human error analysis for ticketing system and doors release system, respectively.
D.1. Human error analysis - Ticketing system
Table 2 – Example of human error analysis for ticketing system
Task Error Mitigation
Select ticket type at ticket vending machine Incorrect ticket type selected Machine buttons labelled with the various ticket types
Machine visual display showing ticket type selected
Select destination at ticket vending machine Incorrect destination selected Machine buttons labelled with the various destinations
Machine visual display showing destinations
Enter coins into ticket vending machine Coins inserted into the notes reader Ticket vending machine has coin slot labelled
Enter notes into ticket vending machine Notes inserted into the coins slot Ticket vending machine has the notes reader labelled
Notes inserted upside down or back to front Machine labelled with a diagram showing the correct note orientations
Transport the ticket Ticket bent in transit “Do not bend this ticket” marked on the ticket
Ticket made from flexible plastic to avoid damage
Ticket size allows ticket to be placed in a wallet or purse Ticket dropped or crushed
Insert ticket into ticket reader Ticket inserted upside down “Travel Card” marked on upside of the ticket
Ticket inserted back to front Direction arrow marked on the upside of the ticket
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D.2. Human error analysis – Doors release system
© State of NSW through Transport for NSW 32 of 36
Table 3 – Example of human error analysis for doors release system
Task Error Mitigation
Locate doors release button Button not located Button labelled with doors release
Button illuminated with green lights
Press doors release button Button not pressed Button labelled with doors release
Button illuminated with green lights
Travel on train Button pressed accidently Button recessed to avoid accidental presses
Button must be pressed for 3 seconds to activate
Button obscured by passengers Door labelled requesting passengers to stand clear
Button damaged by passengers Button recessed to avoid accidental contact
Button made from material that can withstand high impacts
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Appendix E Example of maintenance requirements analysis - Station escalator
© State of NSW through Transport for NSW 33 of 36
Table 4 provides an example of maintenance requirements analysis for station escalator.
Table 4 – Example of maintenance requirements analysis for station escalator
Maintenance item
Functions associated
Possible failures modes
Effect Escalation effect
Failure recognition
Maintenance task options
Maintenance task intervals
Platforms Entry and exit access
Unable to provide entry or exit access
Platform blocked to passengers
Passengers unable to use the escalator
Visual inspections for damage
Testing
Replace platform panels
Daily cleaning, inspection and testing
6 monthly service inspection and testing
Steps Support standing or walking passengers
Unable to support passengers
Steps not safe for passengers
Passengers unable to use the escalator
Visual inspections for damage
Testing
Replace steps Daily cleaning, inspection and testing
6 monthly service inspection and testing
Tracks Provides running surface for the steps
Unable to provide running surface for the steps
Steps unable to move
Passengers unable to ride on escalator
Testing Lubricate tracks
Replace tracks
Daily testing
6 monthly service inspection and testing
Provides running surface for the handrails
Unable to provide running surface for the handrails
Handrails unable to move
Passengers unable to use handrail for support
Visual inspections for damage
Testing
Lubricate tracks
Replace tracks
Daily testing
6 monthly service inspection and testing
Drive gears Provides coupling and speed conversion of the motor to the steps
Unable to provide coupling and speed conversion of the motor to the
No or slow movement of steps.
Passengers unable to ride on escalator
Testing Lubricate gears
Replace gears
Daily testing
6 monthly service inspection and testing
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Maintenance item
Functions associated
Possible failures modes
Effect Escalation effect
Failure recognition
Maintenance task options
Maintenance task intervals
steps
Provides coupling and speed conversion of the motor to handrails
Unable to provide coupling and speed conversion of the motor to handrails
No or slow movement of handrails
Passengers unable to use handrail for support
Testing Lubricate gears
Replace gears
Daily testing
6 monthly service inspection and testing
Hand rails Provides support and stability to passengers
Handrails unable to support passengers
No handrails Passengers unable to use handrail for support
Visual inspections for damage
Testing
Replace handrails Daily cleaning, inspection and testing
6 monthly service inspection and testing
Motors Provides driving force for handrails and steps
Unable to drive the handrails or steps
No or slow movement of steps or handrails
Passengers unable to ride on escalator
Testing Replace motors Daily testing
6 monthly service inspection and testing
Control system
Regulates speed of steps and handrails
Unable to drive the handrails or steps
No or slow movement of steps or handrails
Passengers unable to ride on escalator
Testing Replace motors Daily testing
6 monthly service inspection and testing
Emergency stop system
Halts movement of steps and handrails in an emergency situation
Unable to halt steps and handrails
Steps and handrail movement
Passenger injuries
Testing Replace components Daily testing
6 monthly service inspection and testing
Glass screens
Protects passengers from moving components
Unable to protect passengers from moving components
Exposed moving parts
Passenger injuries
Visual inspections for damage
Replace components Daily inspection
Protects passengers Unable to protect
Passengers Passenger Visual inspections for
Replace components Daily inspection
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Maintenance item
Functions associated
Possible failures modes
Effect Escalation effect
Failure recognition
Maintenance task options
Maintenance task intervals
from falling passengers from falling
fall off steps injuries damage
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Appendix F Example of FRACAS incident report – CPU motherboard Table 5 provides an example of FRACAS incident report for CPU mother board.
Table 5 - Example of FRACAS incident report for CPU motherboard
FRACAS No. Company name System name Part description Part number Opened by Opened date
Closed date
F-0001 Cyberdyne Systems T-101 CPU Core CPU-XXX-001 John Connor 13/05/2015 30/06/2015
Description of problem Description of failure analysis Description of corrective action taken Remarks
Central Computer Motherboard failure Visual inspection revealed solder bridging address bus tracks on central computer motherboard, leading to CPU core failure
Automate component placement and soldering process to reduce human error
Resin-coat PCB prior to component placement and soldering to reduce solder splash impact
Increase lot inspection frequency of motherboard PCB manufacturing process
Corrective actions to be implemented in next scheduled production run on 01 July 2015
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