Process management for avionics - Defining and performing highly accelerated tests in aerospace systems - Application guide

IEC/TS 62500:2008(E) specifies the targets assigned to highly accelerated tests, their basic principles, their scope of application and their implementation procedures. Is primarily intended for programme managers, designers, test managers, and RAMS experts to facilitate the draft of the specification and execution of highly accelerated tests. Is applicable to all programmes and is of primary interest to the industrial firms in charge of designing, developing and producing equipment built for these programmes, and also their customers.

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Status
Published
Publication Date
24-Jul-2008
Current Stage
PPUB - Publication issued
Start Date
25-Jul-2008
Completion Date
25-Jul-2008
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IEC TS 62500:2008 - Process management for avionics - Defining and performing highly accelerated tests in aerospace systems - Application guide
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IEC/TS 62500
Edition 1.0 2008-07
TECHNICAL
SPECIFICATION
Process management for avionics – Defining and performing highly accelerated
tests in aerospace systems – Application guide
IEC/TS 62500:2008(E)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC/TS 62500
Edition 1.0 2008-07
TECHNICAL
SPECIFICATION
Process management for avionics – Defining and performing highly accelerated
tests in aerospace systems – Application guide
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
ICS 03.100.50; 31.020; 49.060 ISBN 2-8318-9933-8
® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – TS 62500 © IEC:2008(E)
CONTENTS

FOREWORD...........................................................................................................................4

INTRODUCTION.....................................................................................................................6

1 Scope...............................................................................................................................7

2 Terms and definitions .......................................................................................................7

3 Acronyms .........................................................................................................................9

4 Highly accelerated test goals and principles ...................................................................10

4.1 General characteristics..........................................................................................10

4.2 General principles of highly accelerated tests........................................................11

4.3 Example of the limitations of highly accelerated tests ............................................13

5 Industrial technical domains covered by highly accelerated tests....................................14

6 Highly accelerated tests in the lifecycle and associated assembly levels ........................14

7 Planning and management of highly accelerated tests....................................................16

7.1 General .................................................................................................................16

7.2 Validation and verification .....................................................................................16

7.3 Planning of highly accelerated tests ......................................................................17

7.4 Management of highly accelerated tests................................................................18

8 General methodology for implementing highly accelerated tests .....................................18

8.1 Structure of the approach ......................................................................................18

8.2 Analysis of product sensitive points.......................................................................19

8.3 Selection of applicable stresses ............................................................................20

8.4 Producing a test plan.............................................................................................21

8.5 Performing tests ....................................................................................................23

8.6 Analysis of test results, corrective action and resumption of testing.......................24

9 Building on and using experience ...................................................................................24

9.1 General .................................................................................................................24

9.2 Creating the database ...........................................................................................25

9.3 Inclusion in the company reference system ...........................................................25

9.4 Use of results for environmental stress screening..................................................25

9.5 Correlation with feedback ......................................................................................26

9.6 Synthesis and impact on company culture .............................................................26

10 Customer/supplier relations ............................................................................................26

10.1 Prime contractor/supplier relations ........................................................................26

10.1.1 Responsibilities .........................................................................................26

10.1.2 Contract procedures ..................................................................................27

10.1.3 Tests synthesis..........................................................................................27

10.2 Supplier/test laboratory relations ...........................................................................27

11 Costs and savings ..........................................................................................................28

11.1 General .................................................................................................................28

11.2 "Non-reliability" costs ............................................................................................28

11.2.1 Cost in delayed time to market ..................................................................28

11.2.2 Cost of an in-service failure .......................................................................29

11.2.3 Cost of a recovery operation......................................................................30

11.2.4 Impact on brand image ..............................................................................30

11.3 Expenses generated by the highly accelerated tests..............................................30

11.3.1 Engineering upstream of testing ................................................................30

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TS 62500 © IEC:2008(E) – 3 –

11.3.2 Test resources used ..................................................................................31

11.3.3 Manpower dedicated to highly accelerated tests ........................................31

11.3.4 The cost of damaged or destroyed products ..............................................31

Annex A (informative) Comparative characteristics of highly accelerated tests and

reliability tests ......................................................................................................................32

Annex B (informative) Example of potential effectiveness table for stresses or loadings

according to the nature of the product sensitive point ...........................................................33

Annex C (normative) Highly accelerated tests implementation logic .....................................34

Annex D (informative) Margin-related statistical considerations – Example:

telecommunications circuit boards or board assembly...........................................................36

Bibliography..........................................................................................................................38

Figure 1 – Exploration of margins using a highly accelerated test .........................................13

Figure 2 – Financial losses generated by a delay in time to market.......................................29

Figure C.1 – General logical flowchart ..................................................................................34

Figure C.2 – Details of test performance...............................................................................35

Figure D.1 – Examples of the margin options open to the designer .......................................37

Table A.1 – Comparative characteristics of highly accelerated tests and reliability

tests .....................................................................................................................................32

Table B.1 – Example of potential effectiveness table for stresses or loadings according

to the nature of the product sensitive point ...........................................................................33

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– 4 – TS 62500 © IEC:2008(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PROCESS MANAGEMENT FOR AVIONICS –
DEFINING AND PERFORMING HIGHLY
ACCELERATED TESTS IN AEROSPACE SYSTEMS –
APPLICATION GUIDE
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

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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.

The main task of IEC technical committees is to prepare International Standards. In

exceptional circumstances, a technical committee may propose the publication of a technical

specification when

• the required support cannot be obtained for the publication of an International Standard,

despite repeated efforts, or

• the subject is still under technical development or where, for any other reason, there is the

future but no immediate possibility of an agreement on an International Standard.

Technical specifications are subject to review within three years of publication to decide

whether they can be transformed into International Standards.

IEC 62500, which is a technical specification, has been prepared by IEC technical committee

107: Process management for avionics.
---------------------- Page: 6 ----------------------
TS 62500 © IEC:2008(E) – 5 –

This technical specification cancels and replaces IEC/PAS 62500 published in 2006. This first

edition constitutes a technical revision.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
107/79/DTS 107/90/RVC

Full information on the voting for the approval of this technical specification 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.

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

• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
---------------------- Page: 7 ----------------------
– 6 – TS 62500 © IEC:2008(E)
INTRODUCTION

In an increasingly harsh economic context (tighter performance requirements, shorter

development cycles, reduced cost of ownership, etc.), it is essential to ensure product

maturity rapidly and, in any case, by the time of commissioning.

It is with a view to remedying shortcomings in traditional development methods that "highly

accelerated" tests have been developed. The main underlying principle behind this new type

of test strategy is as follows: rather than reasoning in terms of conformity with a specification

and simply performing conventional tests, it is on the contrary attempted to push the product

to its limits by applying environmental stresses and/or stimuli of levels higher than the

specification. The aim is thus to take full advantage of current technologies, by eliminating

defects which generate potential failures, as of the first prototypes.

A well-conducted accelerated test process should, in a relatively short time, lead to a

significant increase in the robustness of a product, as early as the initial prototypes stage at

the beginning of the development phase, thus accelerating early maturity of this product.

Furthermore, identification of the margins available on a "mature" product helps to design and

size its future environmental stress screening profile more accurately, by increasing the

severity of the loadings applied to just what is needed, leading to a particularly significant

boost in the efficiency of this environmental stress screening process.
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TS 62500 © IEC:2008(E) – 7 –
PROCESS MANAGEMENT FOR AVIONICS –
DEFINING AND PERFORMING HIGHLY
ACCELERATED TESTS IN AEROSPACE SYSTEMS –
APPLICATION GUIDE
1 Scope

This technical specification specifies the targets assigned to highly accelerated tests, their

basic principles, their scope of application and their implementation procedures. It is primarily

intended for programme managers, designers, test managers, and RAMS experts to facilitate

the draft of the specification and execution of highly accelerated tests. This guide is

applicable to all programmes and is of primary interest to the industrial firms in charge of

designing, developing and producing equipment built for these programmes, and also their

customers who, in drafting contractual clauses, may require that their suppliers implement

highly accelerated tests.

NOTE This technical specification applies to all types of equipment used in systems developed in these

programmes, whatever their nature (electronic, electromechanical, mechanical, electro-hydraulic, electro-

pneumatic, etc.) and whatever their size, from "low-level" subassemblies (PCBs, mechanical assemblies,

connectors, etc.), up to system level groups of equipment.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

NOTE Most of the terminology used in this technical specification conforms to that used in Recommendation

RG.Aéro 000 27. For the other terms, it relies on those used in other documents, such as ET 99.04 (see

Bibliography).
2.1
step stressing
gradual step-wise increase in the level of stress applied to a product
2.2
hard failure

failure which does not disappear on returning to a lower stress level and which can only be

eliminated by repair
2.3
soft failure

failure appearing after a certain given stress level, which disappears when the stress falls

back below this level
2.4
extrinsic defect

fault or weakness inherent in the design of a product or its manufacturing processes and the

elimination of which, presumed to be economically feasible, leads to an improvement in its

operating and/or destruction margins

NOTE This type of defect, which is always the result of a deviation from standard best practices, is not by

definition related to the intrinsic limit imposed by the technologies used.
2.5
intrinsic defect

defect related to the component design, materials, processing, assembly or packaging and

provoked under circumstances within the component's design specifications
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– 8 – TS 62500 © IEC:2008(E)
2.6
latent defect

defect which originally exists in the equipment but has not yet been precipitated and is thus

as yet undetectable by conventional performance checks on this equipment
2.7
patent defect

defect in a component which, after being precipitated, has become detectable by conventional

performance checks

NOTE A patent defect thus stems from a latent defect which has evolved following application of appropriate

stresses (e.g. temperature, vibrations, etc.) and which thus becomes detectable by a performance check.

2.8
environmental stress screening
ESS

set of production process tasks consisting in applying to the equipment concerned, within the

limits permitted by its design, particular environmental stresses in order – during

manufacturing – to reveal and eliminate the largest possible number of extrinsic defects

which, in all probability, would have appeared once utilisation had begun (early life failures)

2.9
accelerated test

test, the aim of which is to predict the behaviour and/or lifetime of a product in its operational

conditions of use, by subjecting it to stresses harsher than the values expected during its

lifespan profile

NOTE Contrary to highly accelerated testing, a "conventional" accelerated test (time/stress exchange) always

relies on one or more analytical lifetime and damage models.
2.10
highly accelerated test

test during which the product or some of its component parts are subjected to environmental

and/or operating stresses that are increased progressively to values far in excess of the

specified values, up to the operating and/or destruction limits of the product

NOTE The rise in exposure time or number of cycles, whether or not associated with a combination of certain

stresses raised to values close to or equal to the specification (or stresses whose nature is not specified) may

meet the same targets as those of the highly accelerated tests, as defined in this technical specification.

2.11
reliability

ability of a product to perform a required function, in given conditions, for a given time interval

NOTE This characteristic is generally expressed by a probability.
2.12
destruction limit

level of stress above which the product will suffer irreversible damage and will no longer be in

conformity with nominal performance once the stress level is returned to below the specified

value (notion of irreversibility)
2.13
operating limit

stress level above which the product no longer functions nominally. When the stress is

returned to below this level, product performance returns to nominal (notion of reversibility)

---------------------- Page: 10 ----------------------
TS 62500 © IEC:2008(E) – 9 –
2.14
fundamental limit

intrinsic limit determined by the technology of a product or particular component, with respect

to a given stress (temperature, vibration, electrical voltage, etc.). This limit, whether or not

destructive, is an absolute barrier and cannot therefore be attributed to a extrinsic defect

EXAMPLE: Melting temperature of a plastic, maximum junction temperature of a semiconductor, yield strength of a

material, etc.
2.15
operating margin
for a given stress, difference between the operating limit and the specification
2.16
destruct margin
for a given stress, difference between the destruct limit and the specification
2.17
maturity

attainment of a product status for which its functional and operational performance can be

considered stabilised with respect to the specifications

NOTE Maturity is the result of a gradual process of eliminating extrinsic defects still present in the product and

the associated processes. This process is called maturing.
2.18
precipitation

transformation, using appropriate stresses, of a latent defect (not yet detectable) into a patent

defect (detectable)
2.19
robustness

property of a product indicating reduced sensitivity of its performance to changes in the

environmental stresses to which it is subjected, to component variation and to drifts in its

manufacturing processes

NOTE Robustness to a large extent is the result of action taken to obtain sufficient operating margins while at the

same time reducing all forms of variability.
2.20
reliability, availability, maintainability, safety
RAMS

range of capabilities of a product enabling it to achieve specified functional performance, at

the required time, for the required duration, without damage to itself or its environment

2.21
failure modes and effects analysis
FMEA

qualitative method of reliability analysis which involves the study of the fault modes which can

exist in every sub-item of the item and the determination of the effects of each fault mode on

other sub-items of the item and on the required functions of the item
3 Acronyms
• CDR: Critical Design Review.
• FMEA: Failure Modes and Effects Analysis.
• EMC: Electromagnetic Compatibility.
• ESS: Environmental Stress Screening.
---------------------- Page: 11 ----------------------
– 10 – TS 62500 © IEC:2008(E)
• FRACAS: Failure Reporting and Corrective Action System.
• HAT: Highly Accelerated Test
• MTBF: Mean Time Between Failures.
• PCB: Printed Circuit Board.
• PDR: Preliminary Design Review.
• PRA: Preliminary Risk Analysis.
• RAMS: Reliability, Availability, Maintainability, Safety.
• RS: Requirements Specification.
• RTV: Rapid Temperature Variation.
• TTM: Time To Market.
4 Highly accelerated test goals and principles
4.1 General characteristics

A highly accelerated test is a test in which the product or some of its component parts are

subjected to environmental and/or operating stresses which are gradually raised to values in

excess of the specified values, until the product operating and/or destruction limits are

reached.
The primary purpose of highly accelerated tests is to contribute to:

– improving the robustness of the product, by eliminating the weaknesses inherent in the

product design and/or processes, and in the technologies used;
– obtaining products that are mature as of the first production article;
– improving the reliability and lifespan of the product in service;
– reducing development times and costs;
– specifying optimal environmental stress screening.
Attaining these goals involves:

– detecting extrinsic defects as early as possible (so that they can be corrected), as these

defects are inherent in design errors or insufficient control of the manufacturing

processes,

– exploration of the operating limits, once extrinsic defects have been eliminated so that,

whenever applicable, they can be pushed back through new design choices, when the

margins in relation to the specified operating range appear inadequate.

Instead of reasoning in terms of conformity with the specification, which is a poor way of

reflecting the product's real lifespan profile, it is on the contrary attempted to push the product

to breaking point (often up to failure), using environmental stresses or various stimuli at levels

far in excess of the specifications, in order to reveal, identify, then correct the extrinsic

defects still present. This implies on the one hand exploration of the available margins, and

on the other, improving these margins through appropriate action on the design of the product

itself or its manufacturing processes (see Annex D).

Owing to the adopted definition for the highly accelerated test, the following characteristics of

this type of highly accelerated test can be identified:

– A highly accelerated test is a proactive type of test: it is here understood that a highly

accelerated test should be considered as a tool to support the design of the product and

its processes and that it normally leads to engineering activities aimed at understanding

the failure mechanisms observed, in order to provide the corrections felt to be

economically feasible and which will enable them to be eliminated or at least delay their

---------------------- Page: 12 ----------------------
TS 62500 © IEC:2008(E) – 11 –

evolution. The highly accelerated test is "proactive" in that it encourages these

engineering actions at the earliest stage in development.

– A highly accelerated test is not a conformity test: through the desire to explore the

margins and expand them if necessary, the highly accelerated test looks above all to

reveal the product defects which generate failures when working beyond the

specifications. It is therefore the opposite of a conformity test, which simply aims to

ensure that the product's performance is correct when it is subjected to the specific

operating and environmental conditions.
– A highly accelerated test should not be confused with an ordinary margins

verification test: a margins verification test in fact simply aims to ensure that product

performance remains correct when the stress values are raised to predetermined values

above the specified values, whatever the initially adopted margin. Consequently, the

margins verification test consists in practice in applying an extra coefficient to certain

specified stresses (referred to as the "regulation coefficient" in certain mechanical

professions). It is similar to a conformity test, even if it deals with performance conformity

in operating conditions which are outside the specified range. The highly accelerated test,

for its part, establishes operating and/or destruction margins for the product.

– A highly accelerated test should not be confused with a "conventional" accelerated

lifespan test: the purpose of an accelerated lifespan test is in fact to predict the evolution

of the behaviour of a product in its operational conditions of use, by subjecting it to

stresses that are harsher than the values expected during its lifespan profile. To do this,

the accelerated test
...

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