SIST EN 3197:2011

SLOVENSKI STANDARD
01-maj-2011
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Aerospace series - Design and installation of aircraft electrical and optical
interconnection systems
Luft- und Raumfahrt - Konstruktion und Installation elektrischer und optischer
Verkabelung in Luftfahrzeugen
Série aérospatiale - Conception et installation des organes de raccordements électriques
et à fibres optiques sur avions
Ta slovenski standard je istoveten z: EN 3197:2010
ICS:
49.090 2SUHPDLQLQVWUXPHQWLY On-board equipment and
]UDþQLKLQYHVROMVNLKSORYLOLK instruments
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 3197
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2010
ICS 49.060; 49.090
English Version
Aerospace series - Design and installation of aircraft electrical
and optical interconnection systems
Série aérospatiale - Conception et installation des organes Luft- und Raumfahrt - Konstruktion und Installation
de raccordements électriques et à fibres optiques sur elektrischer und optischer Verkabelung in Luftfahrzeugen
avions
This European Standard was approved by CEN on 30 July 2010.

CEN 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 CEN-CENELEC Management Centre or to any CEN 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 CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same
status as the official versions.

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

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2010 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 3197:2010: E
worldwide for CEN national Members.

Contents Page
Foreword .3
ORGANISATION OF THIS STANDARD (Detailed organisation may be found in Annex A) .4
1 Scope .5
2 Normative references .5
3 Terms and definitions .6
4 Limitations .6
5 General requirements .6
6 Selection of EWIS and OFIS Components . 19
7 EWIS Components Identification . 45
8 Separation and principles to apply . 48
9 Installation and manufacturing principles . 60
10 Modification and repairs by STC applicants . 84
11 EWIS and OFIS Safety . 86
Annex A (informative) EN 3197 detailed content . 87
Annex B (normative) Main normative references and ASD-STAN Technical Reports per family
of products . 95
B.1 Quality and General standards . 95
B.2 Wires and cables. 96
B.3 Optical fibre cables, connectors and contacts . 98
B.4 Connectors and contacts . 99
B.5 Protective devices . 102
B.6 Switching devices . 103
B.7 Terminal junctions . 103
B.8 Terminal lugs and in-line splice . 104
B.9 Ties . 104
B.10 Solder sleeves . 104
B.11 Bonding leads . 105
B.12 Clamps . 105
B.13 Protective parts . 105
B.14 Identification parts . 106
B.15 Installation Components . 106
B.16 Lamps . 107
Annex C (informative) Differences of electrochemical potentials between some conductive
materials (in mV) . 108

Foreword
This document (EN 3197:2010) has been prepared by the Aerospace and Defence Industries Association of
Europe - Standardization (ASD-STAN).
After enquiries and votes carried out in accordance with the rules of this Association, this Standard has
received the approval of the National Associations and the Official Services of the member countries of ASD,
prior to its presentation to CEN.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by June 2011, and conflicting national standards shall be withdrawn at
the latest by June 2011.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
ORGANISATION OF THIS STANDARD
(Detailed organisation may be found in Annex A)
1 Scope page 5
Description of the aim of this document.
2 Normative references page 5
List of Normative references used.
3 Terms and definitions page 6
List of particular definitions or mentions of particular applicable documents.
4 Limitations page 6
Applicability of this document.
5 General requirements page 6
General and important considerations, plus specific requirements linked to particular areas of use.
6 Selection of EWIS and OFIS Components page 19
Guideline for the choice of necessary components.
7 EWIS and OFIS Components Identification page 45
Description of necessary identifications for components, bundles, equipements and repairs.
8 Separation and principles to apply page 48
Rules to satisfy for a good integration and behaviour of systems.
9 Installation and manufacturing principles page 60
Description of installation and manufacturing principles.
10 Modification and repairs by STC applicants page 84
11 EWIS and OFIS Safety page 86
Safety analysis.
NOTE Inside this standard, texts in italic come from official texts and cannot be modified without verification.
1 Scope
This European standard provides instructions on the methods to be used when designing, selecting,
manufacturing, installing, repairing or modifying the aircraft electrical and optical interconnection networks,
now called Electrical Wiring Interconnection System (EWIS), and Optical Fibre Interconnection Systems
(OFIS), subjects to the limitations defined in Clause 4 of this standard.
The general content of this standard is described in page 2.
A detailed content of this standard is given in Annex A.
This standard lists all the relevant European standards related to EWIS and OFIS in Annex B.
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.
EN 60270, High-voltage test techniques — Partial discharge measurements (IEC 60270:2000)
ISO 2574, Aircraft — Electrical cables — Identification marking
ISO 2685, Aircraft — Environmental test procedure for airborne equipment — Resistance to fire in designated
fire zones
ISO 4046-1, Paper, board, pulps and related terms — Vocabulary — Part 1: Alphabetical index
ISO 7137, Aircraft — Environmental conditions and test procedures for airborne equipment
1)
MIL-DTL-22520G, Revision G General Specification for Crimping Tools, Wire Termination — Entire Set
1)
MIL-STD-202, Test method standard electronic and electrical component parts
1)
MIL-T-43435B, Military specification tape, lacing and tying
2)
TR 4684, Aerospace series — Electrical technology and components definitions
2)
TR 9535, Aerospace series — Substance declaration
2)
TR 9536, Aerospace series — Declarable Substances Recommended Practice
3)
AS 81824/1, Splice, electric, permanent, crimp style copper, insulated, environment resistant, class 1
AS 83519, Shield termination, solder style, insulated, heat-shrinkable, environment resistant with pre installed
3)
leads for cables having tin or silver plated shields (class I)

1) Published by: Department of Defense (DoD), http://www.defenselink.mil/.
2) Published as ASD-STAN Technical Report at the date of publication of this standard by Aerospace and Defence
Industries Association of Europe-Standardization (ASD-STAN), (www.asd-stan.org).
3) Published by: Society of Automotive Engineers (SAE), (www.sae.org).
ASTM D 1868, Standard Test Method for Detection and Measurement of Partial Discharge (Corona) Pulses in
4)
Evaluation of Insulation Systems
NOTE Related to EWIS and OFIS, all today existing ASD Normative references per family of products may be found
in Annex B.
3 Terms and definitions
For the purposes of this document, the terms and definitions given in TR 4684 and the following apply.
3.1
Design Authority
in this document, this term covers the Companies, in charge of the original design or to give the design
agreement for which Certification will be required from the Regulatory Authorities
3.2
Regulatory Authority
in this document, this term covers the Organisations in charge to write rules to satisfy, to survey the design
and to grant Navigability Certificate, like EASA and FAA
4 Limitations
It is recognized that the installation practices contained in this standard do not necessarily represent the full
requirements for a safe and satisfactory electrical and optical interconnection system.
In the event of a conflict between the text of this document and the references cited herein, the text of this
document takes precedence. However, nothing written in this standard shall override the specific
requirements of a Design Authority, the Airworthiness Requirements, applicable laws or any regulation from
the regulatory authorities, unless a specific exemption has been obtained.
5 General requirements
5.1 Applicable Rulemaking
The main rulemakings to satisfy for the definition of the various possible electrical installations on large
aircrafts are coming from:
 Design technical requirements
From the EASA European Aviation Safety Agency (CS 25) and the FAR Federal Aviation Regulation (14CFR –
Part 25).
 Organisation requirements
From the EASA European Aviation Safety Agency (IR 21) and the FAR Federal Aviation Regulation (14CFR –
Part 21).
4) Published by: American Society For Testing and Materials (ASTM), http://www.astm.org/.
Important advices:
a) From the P2 issue, this standard includes the EWIS concept and associated consequences which were
introduced in the regulation by the FAA in November 2007 and by the EASA in autumn 2008. This was
also the opportunity for the authorities to group all the electrical requirements: the rules 25.17xx.
b) CS or FAR 23, 27 and 29 which concern small aircraft, small and large helicopters were not updated
in-line.
5.2 EWIS Definition
The definition of the aircraft electrical interconnection network, now called Electrical Wiring Interconnection
System (EWIS) is now given in the regulation. The retained text, coming from the EASA, is the following:
«CS 25.1701 Electrical Wiring Interconnection System Definition
(a) Electrical wiring interconnection system (EWIS) means any wire, wiring device, or combination of these,
including termination devices, installed in any area of the airplane for the purpose of transmitting electrical
energy between two or more intended termination points. Except as provided for in Subclause (c) of this
Subclause, this includes:
1) Wires and cables.
2) Bus bars.
3) The termination point on electrical devices, including those on relays, interrupters, switches,
contactors, terminal blocks and circuit breakers, and other circuit protection devices.
4) Connectors, including feed-through connectors.
5) Connector accessories.
6) Electrical grounding and bonding devices and their associated connections.
7) Electrical splices.
8) Materials used to provide additional protection for wires, including wire insulation, wire sleeving, and
conduits that have electrical termination for the purpose of bonding.
9) Shields or braids.
10) Clamps and other devices used to route and support the wire bundle.
11) Cable tie devices.
12) Labels or other means of identification.
13) Pressure seals.
(b) The definition in Subclause (a) of this Subclause covers EWIS components inside shelves, panels, racks,
junction boxes, distribution panels, and back-planes of equipment racks, including, but not limited to, circuit
board back-planes, wire integration units and external wiring of equipment.
(c) Except for the equipment indicated in Subclause (b) of this Subclause, EWIS components inside the
following equipment, and the external connectors that are part of that equipment, are excluded from the
definition in Subclause (a) of this Subclause:
1) Electrical equipment or avionics that is qualified to environmental conditions and testing procedures
when those conditions and procedures are:
i) Appropriate for the intended function and operating environment, and
ii) Acceptable to the Agency.
2) Portable electrical devices that are not part of the type design of the aeroplane. This includes
personal entertainment devices and laptop computers.
3) Fibre optics».
5.3 OFIS Definition
The definition of the aircraft optical fibre interconnection network, now called Optical Fibre Interconnection
System (OFIS) was created by similarity. The retained text is the following:
"OFIS means any fibre or cable, including termination devices, installed in any area of the aircraft for the
purpose of transmitting optical signals between two or more intended termination points. Except as provided
for in Subclause (c) of this Subclause, this includes:
1) Fibres and cables.
2) Optical Data buses.
3) The termination point on fibre optic transmitting sources and receiving devices protection devices.
4) Connectors, including feed-through connectors.
5) Connector accessories.
6) Fibre optic splices.
7) Materials used to provide additional protection for fibres and cables, including insulation, and conduit.
8) Clamps and other devices used to route and support the cable bundle.
9) Cable tie devices.
10) Labels or other means of identification.
11) Pressure seals.
a) The definition in Subclause (a) of this Subclause covers OFIS components inside shelves, panels, racks,
junction boxes, distribution panels, and back-planes of equipment racks.
b) Except for the equipment indicated in Subclause (b) of this Subclause, OFIS components inside the
following equipment, and the external connectors that are part of that equipment, are excluded from the
definition in Subclause (a) of this Subclause:
1) Fibre optic equipment or avionics that is qualified to environmental conditions and testing procedures
when those conditions and procedures are:
i) Appropriate for the intended function and operating environment, and
ii) Acceptable to the Agency"
Particular information on OFIS may be found in EN 4533-001 to EN 4533-004. (See also particular Annex B3).
5.4 Design precedence
Design of the EWIS and OFIS shall conform to the following precedence:
st
1 – Safety;
nd
2 – System requirements;
rd
3 – The ease of maintenance, removal and replacement of the cabling;
th
4 – Cost effective aircraft production.
Cabling shall be fabricated and installed so as to achieve the following:
a. Maximum reliability;
b. Minimum interference and coupling between systems;
c. Accessibility for inspection and maintenance including cleaning;
d. Prevention of damage.
5.5 Selection considerations
Parts, materials, directives and procedures covered by existing European Standards shall be given preference
by Design Authorities for all new European projects wherever suitable.
This standard lists all the relevant European standards related to EWIS and OFIS in Annex B.
Otherwise the parts, materials, directives and procedures shall meet the levels of performance and safety as
required by the regulatory authorities.
5.6 Service life
In normal use conditions, the airframe electrical and fibre optic interconnection systems and its EWIS and
OFIS components shall be selected and installed so that their service life is not less than that of the aircraft
structure, which for a civil plane is generally 60 000 flying hours or 20 years, unless otherwise specified.
It shall not, however, be assumed that all EWIS and OFIS components will always achieve this life and
installations should be designed to permit a satisfactory level of inspection, test and repair according to rule
25.1725.
Similarly, for engines/power plants and undercarriages which normally have a minimum service life of
10 000 hours, but where, due to their modular construction, the interconnection system, or parts thereof, are
required to have longer service lives, the system design shall permit satisfactory inspection, test and repair.
For devices and sub-systems which are designed to be disconnected, the number of acceptable mating
unmating operations shall be specified in the relevant technical specifications.
5.7 Smoke and Fire Hazards
Components of the interconnection systems defined in this standard have been designed with an awareness
of the hazards of smoke and toxic products under failure conditions. General test requirements may be found
in EN 2825 and EN 2826 and dedicated test method may be found in the relevant component specifications
(for example: for electrical cables see EN 3475-601 and EN 3475-602).
It is the responsibility of the designer to avoid the use of materials which, in any likely conditions of use or
abuse, could create a severe failure condition.
When necessary the design of EWIS and OFIS installations shall recognize the need to provide adequate
protection or separation of cables and cable harnesses.
Flammability and self-extinguishing requirements shall be specified for all EWIS and OFIS components and it
shall be noted that these requirements are intended to minimize, for example, the transmission of fire along
cables or the propagation of fire by the release of flaming droplets.
Nevertheless, the installation of EWIS and OFIS shall recognize that severe overheating of electrical cables is
a possibility, therefore the maximum number and size of cables with associated loads within the cable harness
shall be considered, see EN 2853 for calculation.
Particular care shall be given to the torqueing of terminal lug screws.
When considering the acceptability of wire or fibre optic, reference should be made to EN 3475 or EN 3745
respectively, or alternative standards acceptable to the design authority, defining acceptable test methods,
including arc-tracking test methods (see next Subclause).
Damaged wire and insulation can cause electrical arcing, providing the spark that can cause fire. It should be
noted that contamination by materials such as dust, dirt, lint, vapours, etc. can provide fuel for fire.
Owing to potential fire hazard, silver-plating shall not be used in areas where they are subject to
contamination by ethylene glycol solutions unless suitable protection features are employed.
CASE OF SMALL NON METALLIC PARTS
Small parts are those that would not contribute significantly to the propagation of a fire as knobs, handles,
rollers, fasteners, clips, grommets, rub strips, pulleys, and small electrical parts.
When these parts are grouped together in the same zone, virtual volume are equivalent and shall be taken
into consideration. Verification of flammability behaviour shall be done, for example on a reference
homogenous material specimen of 50 mm wide and 30 cm length.
Shall be taken into account in particular:
 Self extinguishing,
 Smoke density,
 Gas emission toxicity,
 Dripping must not ignite a flammable product (paper as ISO 4046).
5.8 Short-Circuit and Arc-Tracking
Experience has shown that people examining fault damages may confuse these two phenomena. So the
following Subclauses propose means to differentiate both and give technical information to explain the
Arc-tracking phenomenon.
5.8.1 Short-Circuit description
5.8.1.1 Cause
A phenomenon of electrical origin generating an over current (with or without an electric arc), which causes
local deterioration of one or more cables (conductor and insulation) by thermal effect.
The origin of this phenomenon is direct contact:
 between at least two conductors (cable core)
 of a conductor with the structure
with different electric voltages.
The over current then appears in the damaged circuit thus causing the protection device located upstream
(circuit-breaker, fuse, etc.) to trip.
The duration of the short-circuit is short (a few milliseconds to a few tenths of a second).
5.8.1.2 Effects on electric cable looms
The deterioration depends on the power flowing in the circuit.
With high short circuit current deterioration of collateral cables may occur.
Cable damage generally does not exceed 50 mm length (25 mm on either side of the defect point).
5.8.2 Arc-Tracking description
5.8.2.1 Cause
The origin of this phenomenon is contact between at least two conductors (cable core) with different electric
voltages via a wet (liquid) or dry (chafing on structure or between cables) "resistive" circuit.
This results in the appearance of electric arcs limiting the current in the circuit(s) to an integrated value below
the tripping threshold of the circuit breaker located upstream.
In returning to the source, the electric arc causes cable deterioration (conductor and insulation) by thermal
effect.
As the protection devices do not trip immediately the duration of the arc-tracking phenomenon is relatively
longer than that of a short-circuit, and can last for several seconds.
The phenomenon stops when:
 direct contact occurs between adjacent conductors (short-circuit). The over current then appears in the
damaged circuit thus causing the protection device located upstream (circuit-breaker, fuse, …) to trip.
 current flows stops due to separation of cores (lack of maintaining, blow effect, …).
The phenomenon cannot propagate if:
 the insulation is arc-tracking resistant, or
 a specific device is used to accelerate tripping from the very beginning of arcs appearance.
5.8.2.2 Effects on electric cable looms
Arc-tracking can be differentiated from a short-circuit mainly through the following indications:
• The cable insulation is partly or fully transformed into blackish carbonized residue,
• The cable damage is always located between the initial defect and the supply source,
• The cable damage is generally longer than 70 mm and can extend to hundreds millimetres.
Deterioration of collateral cables may occur.
5.8.3 Arc-tracking phenomenon
5.8.3.1 General
This phenomenon is basically a thermal effect resulting in the conversion of some particular insulating polymer
into an electrically conducting material.
There are various ways to initiate this degradation of the insulation, nevertheless once a power arc is
produced the resultant reaction is the same.
In any case the generator shall have a 1-minute rating of not less than 20 kVA. Similar results are obtained
with higher ratings. Location and tightness of cable-ties are of particular importance to obtain repeatable
results.
Present test methodologies are carried out with 115 Va.c. in order to cover all present existing voltage sources
used on aircraft, three main ways exist, classified as wet test, dry test or wet short circuit test.
Current test methods do not cover new voltages such as 230 Va.c. and ± 270 Vd.c. For these new voltages,
appropriate fault protection is essential particularly where d.c., with its absence of zero voltage crossing
points, is involved.
Combinations of materials may be employed to optimise the performance of an insulating system.
Use of Arc Fault protection, such as AFCB (Arc Fault Circuit-Breaker) is another solution. It can be used to
accelerate tripping from the very beginning of arcs appearance, thus limiting collateral damages.
5.8.3.2 Wet tracking
This is a surface phenomenon that can act over a significant distance.
When failure occurs the conversion proceeds through the bulk of the insulation and results in more extensive
damage (see note below). A continuing supply of electrolyte is required over the polymer surface, bridging
points at different electrical potential typically exposed by some form of damage. When the supply of
electrolyte is at a suitable rate multiple random dry spots on the surface, due to heating in the electrolyte, lead
to very small low current, short duration arcs (scintillation). These arcs have a temperature of 1 000+ degrees
acting over a very tiny area and in a tracking material gradually produce a characteristic “treeing” pattern on
the surface of the insulation. When a branch (or branches) of the “tree” eventually forms a complete path
between the electrodes a sustained high temperature power arc is established. This can lead to an avalanche
effect where the resultant high energy and temperature convert adjacent insulating material, that was not
initially involved, into a thermally and mechanically stable, electrically conducting graphitic material.
The concerned test method is EN 3475-603.
The test was designed to simulate the effect of moisture creating an electrical path between insulation
damage on adjacent cables. This damage may come from insulation ageing or from possible mechanical
aggression for example from bad hot stamp markings.
5.8.3.3 Electrical erosion
Where a material does not produce conductive surface spots the scintillation may lead to the loss, by
evaporation or de-polymerisation, of tiny amounts of insulation whilst leaving the surface chemically unaltered.
In tests for wet tracking it is important that the pass/fail criteria be set to discriminate between violent tracking
failure and the longer term, relatively benign effects resulting from extreme erosion in materials prone to this
effect.
It is important to quote that all insulating systems subjected to a permanent electrical erosion will fail, even
collateral cables. It is just a question of time.
So visual examination of test samples is an important way of discriminating between the arc-tracking and
electro erosion phenomena (see 5.8.2.2).
5.8.3.4 Dry tracking
This is a bulk rather than a surface effect. No electrolyte or moisture is required.
Very localised heating occurs over the cross section of the insulation at the “fault” point. The heating results
from tiny intermittent, short duration, sparks from the bridging of exposed conductors that do not trip a
conventional circuit breaker. Such faults are known as “splashing” or “ticking” faults and may be caused in
service by vibrating conductor to structure contact or flexing of wire with broken conductor strands. Such
sparks act in a similar manner to scintillation and gradually pyrolyse the whole bulk of the insulation producing,
in the case of a tracking polymer, a conducting graphitic structure with the potential for avalanche failure within
a bundle in the same manner as for the wet case above.
Typically in tests for dry tracking the initiation is via a vibrating metal edge which bridges power carrying
conductors at points having different electrical potential.
The concerned test method is EN 3475-604.
The test was designed to simulate the effect of chaffing against structure creating an electrical path between
insulation damage on adjacent cables.
5.8.3.5 Wet short circuit test
This involves the simultaneous shorting, by drops of electrolyte that run down the insulation and across the
exposed flush cut ends of conductors in a wire bundle. The conductors are energised at different potentials
and because of the small inter-conductor distances vigorous arcing is quickly established on all wires. There is
a combination of some surface scintillation between the electrolyte drip point and the conductors but primarily
vigorous arcing over the short distance of the insulation cross section. In a tracking insulation there is rapid
conversion into a graphitic structure and rapid “burn back” towards the electrical source. In a non-tracking
system the conductor itself is gradually eroded within the insulation. The insulation remains as a tube and the
path length between conductors slowly increases to the point where activity ceases.
The concerned test method is EN 3475-605.
The test was designed to simulate the effect of moisture ingress into a connector back shell which, where
bung sealing is faulty, can lead to shorting between rear parts of pins via wire insulation and/or across the
surface of the sealing bung.
5.8.3.6 Notes on arc characteristics
Metal to metal arcs are of high current density and relatively unstable; as such they tend to “cut” conductors
rapidly and thus limit damage to the faulted wire. Graphite to metal and particularly graphite to graphite arcs
are low current density, stable and spread over a large area so that circuit interruption is delayed; this delay
gives time, in tracking materials (only a few milliseconds are required), for the conversion of adjacent
insulation to conducting material and the potential avalanche effects.
5.9 Installation Groups
The design, modification and repair of EWIS and OFIS need to be considered for each of the following groups
according to their specific requirements:
 engine cable harnesses;
 electrical power generation - heavy duty;
 airframe non-pressurized SWAMP (Severe Wind And Moisture Problems) areas;
 general airframe;
 equipment cabling (line replaceable unit boxes, panels and racks, etc.);
 radio- and/or video frequency;
 data bus and/or video digital links;
 optical fibre link.
5.10 Maintenance considerations
The maintainability of EWIS and OFIS including cleaning and inspection shall be a prime consideration in the
selection, design, installation and identification of harnesses, electrical/optical cable assemblies and wiring
system components. All cabling should be accessible, repairable and/or replaceable at the maintenance level
specified by the design authority. Other specific requirements concerning maintenance, such as cleaning
methods, are specified in the appropriate Subclause on the subject.
It shall be noted that EWIS and OFIS of some particular systems or parts may require particular maintenance
considerations, examples: engines, landing gears, fly-by-wire, shielded bundles.
5.11 Materials considerations
5.11.1 General
As a minimum, the selection of EWIS and OFIS materials shall take into account requirements of rule 25.603.
5.11.2 Environmental Directives
Directives, such as EU (RoHS-REACH), relative to electrical components or equipments evolved and call from
now for the prohibition of the use of substances considered to be hazardous, such as lead, cadmium, mercury
and hexavalent chromium, contained in these components or equipments. For particular cases where no
substitutive solution exists, derogation shall be obtained from the authorities.
Some technical reports apply to the aerospace and defence industries and their supply chains:
TR 9535, Aerospace series — Substance declaration
TR 9536, Aerospace series — Declarable Substances Recommended Practice
5.11.3 Metals
The metals used shall be corrosion-resistant or suitably protected for resistance to corrosion throughout the
expected service-life. The maximum potential difference between any two metals in mutual contact should be
300 mV to minimize the risk of electrolytic corrosion unless the junction shall be protected to avoid electrolyte
presence. See Annex C for potential differences between common metals.
5.11.4 Non-metals
All non-metals used, including plastics, fabrics and protective finishes, shall not support micro-organic or
fungus growth, and should not be adversely affected by weathering, applicable fluids, temperature and
ambient conditions encountered while the aircraft is in service.
So as to avoid any hazards to the occupants, they shall:
 meet the relevant flammability requirements of the Design Authority,
 not emit, when burning, a smoke density higher than a specified limit,
 not emit toxic gases with a concentration exceeding specified values.
Cable insulation and protective parts using PVC (Polyvinyl chloride) are absolutely prohibited.
Polyamide materials can be used for cable ties and fitting parts.
Attention is brought on some fluoro-elastomers for which decomposition residus, after fire for example, can be
hazardous.
Wire insulation shall have an arc resistance capability as defined in their own standard.
5.12 Quality
5.12.1 Components Qualification
EWIS and OFIS components shall be qualified for airborne use or specifically assessed as acceptable for the
intended use and be appropriate for the environment in which they are installed, through for example the ASD
Quality management systems and Qualification Procedures defined in EN 9133.
Aircraft manufacturers list approved components in their manuals, such as the standard wiring practices
manual (ATA Chapter 20). Only the components listed in the applicable manual or approved substitutes
should be used for the maintenance, repair, or modification of the aircraft. EWIS and OFIS modifications to the
original type design should be designed and installed to the same standards used by the original aircraft
manufacturer or other equivalent standards acceptable to the Authorities. This is because the manufacturer’s
technical choice of an EWIS and OFIS component is not always driven by regulatory requirements alone. In
some cases specific technical constraints would result in the choice of a component that exceeds the
minimum level required by the regulations.
5.12.2 Processes Qualification
All processes, used for production shall be qualified for airborne use or specifically assessed as acceptable for
the intended use, when available through European Standards such as example EN 2812 for stripping of
electric cables or EN 2242 for crimping of electric contacts.
During maintenance, repair or modification, processes must come from the same standards used by the
original aircraft manufacturer or from other equivalent standards acceptable to the Authorities.
Some particular processes may required qualified operators and this qualification shall be periodically re-
validated.
5.12.3 Test Methods
Test methods used for qualification, validation, expertise, technical comparison should come from recognized
standards and particularly when available from European standards such as examples EN 2591, EN 3475…
(See list of existing standards in Annex B).
5.13 Specific Requirements
5.13.1 Advice
In this particular chapter, only requirements specific to power plants, helicopters and light planes are
highlighted. All other requirements are in accordance with this standard.
5.13.2 Power plant
5.13.2.1 General
Engines have no pressurized zones, but normally operate below an altitude of 50 000 feet for civil aircraft or
100 000 feet for military aircraft.
Engines are generally equipped with several harnesses which can be removed separately and are considered
as equipment. Generally there is no need for functional identification on individual wire or cable.
5.13.2.2 Connectors
a) Selection
Sealed version of connectors and connecting devices are required.
b) Sealing
Contacts shall be fitted in all cavities. All cavities in the rear grommet shall be filled with either a wire, a filler
plug or a wire stub.
c) Mechanical locking
Plugs shall have a self locking device.
Wire locking of coupling nuts is not recommended.
5.13.2.3 Wiring and fastening
a) Minimum bend radius recommended
For solid harness (when cables are strongly clamped together) and interconnection harnesses, minimum bend
radius recommended are:
 5 times to 10 times the diameter of assembly depending on harness technology
 10 times the diameter of the largest cable contained in the bundle.
For particular dynamic installations and design, the minimum bend radius shall be 3 times or 6 times the
bundle during the sequence. (open Nacelle door, pylon / nacelle liaison).
Except with permanent relatives movements
b) Harness clamps
The use of plastic cable ties with internal metallic locking serrations can be used on engine harness bundles
when metallic braids or heat-shrinkable sleeves are covering the cables.
Generally harnesses shall be fixed on engine either together or individually using “P” clamps. Broomhandle
(“W” clips / omega / terry clips) may be used for straight harness runs.
5.13.2.4 Installation
Harnesses should be installed so that they can be removed and refitted without the need to remove other
engine components, such as brackets, pipes etc.
When a harness crosses butting flanges in hot area of engine main casings, sufficient care shall be brought
such that no possible hot gas leakage can damage cable insulation.
The harness shall not be routed parallel to and on top of engine main flanges junction where a hot gas
leakage may destroy the cable insulation.
Consideration shall be given to the following when deciding a cable route:
a) Avoidance of, or protection from, damage during engine installation and maintenance.
b) Avoidance of areas where crash-landing damage would constitute a hazard.
c) Accessibility for maintenance testing, inspection and repair.
d) Avoidance of any position and/or shape which would encourage the use of the harness for handholds or
footrests.
e) Common mode failure of duplicated functions.
f) Minimise physical damage that may result from fire, turbine burst, starter burst, duct burst or fluid
contamination
g) Failure Mode Effect Analysis (FMEA) on signal separation.
h) Removal of harness without disturbance to another system that would necessitate a re-test to that
system.
i) Removal of LRU accessories with minimal harness disturbance.
j) Relative movement between connectors/terminations and fixed points, such as clipping points, terminal
blocks etc.
In the area of fan blade-out containment, special attention shall be taken for the minimum clearance in order
to avoid any hazardous damage.
The connections to accessories which are mounted on vibration isolators shall be carefully considered. The
clipping and harness shall not add loads to the installed accessory outside of defined limits. The accessory
manufacturer shall take into account the connecting hardware (harness and associated clipping) and its spring
rate for the requirements of the anti-vibration system.
5.13.2.5 Separation
On dual channel, electronically controlled engines, harnesses for the two separate channels shall be allocated
to different connectors and the separa
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