SIST EN 4533-004:2018

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.3RSUDYLODLuft- und Raumfahrt - Faseroptische Systemtechnik - Handbuch - Teil 004: Reparatur, Wartung und InspektionSérie aérospatiale - Systèmes des fibres optiques - Manuel d'utilisation - Partie 004 : Réparation, maintenance, nettoyage et contrôleAerospace series - Fibre optic systems - Handbook - Part 004: Repair, maintenance, cleaning and inspection49.060Aerospace electric equipment and systems33.180.01VSORãQRFibre optic systems in generalICS:Ta slovenski standard je istoveten z:EN 4533-004:2018SIST EN 4533-004:2018en,fr,de01-marec-2018SIST EN 4533-004:2018SLOVENSKI
STANDARDSIST EN 4533-004:20091DGRPHãþD



SIST EN 4533-004:2018



EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 4533-004
January
t r s z ICS
v {ä r x r Supersedes EN
v w u uæ r r vã t r r xEnglish Version
Aerospace series æ Fibre optic systems æ Handbook æ Part
r r vã Repairá maintenanceá cleaning and inspection Série aérospatiale æ Systèmes des fibres optiques æ Manuel d 5utilisation æ Partie
r r v ã Réparationá maintenanceá nettoyage et contrôle
Luftæ und Raumfahrt æ Faseroptische Systemtechnik æ Handbuch æ Teil
r r vã Reparaturá Wartung und Inspektion This European Standard was approved by CEN on
t u July
t r s yä
egulations which stipulate the conditions for giving this European Standard the status of a national standard without any alterationä Upætoædate lists and bibliographical references concerning such national standards may be obtained on application to the CENæCENELEC Management Centre or to any CEN memberä
translation under the responsibility of a CEN member into its own language and notified to the CENæCENELEC Management Centre has the same status as the official versionsä
CEN members are the national standards bodies of Austriaá Belgiumá Bulgariaá Croatiaá Cyprusá Czech Republicá Denmarká Estoniaá Finlandá Former Yugoslav Republic of Macedoniaá Franceá Germanyá Greeceá Hungaryá Icelandá Irelandá Italyá Latviaá Lithuaniaá Luxembourgá Maltaá Netherlandsá Norwayá Polandá Portugalá Romaniaá Serbiaá Slovakiaá Sloveniaá Spainá Swedená Switzerlandá Turkey and United Kingdomä
EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre:
Avenue Marnix 17,
B-1000 Brussels
9
t r s z CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Membersä Refä Noä EN
v w u uæ r r vã t r s z ESIST EN 4533-004:2018



EN 4533-004:2018 (E) 2
Contents Page European foreword . 3 Introduction . 4 1 Scope . 5 2 Normative references . 5 3 Fault analysis . 6 3.1 Fault notification . 6 3.2 Symptoms . 6 3.3 Potential faults . 7 3.4 Fault identification and location . 10 4 Repair techniques . 13 4.1 General . 13 4.2 Splice . 13 4.3 Structural repair . 14 4.4 Terminus recovery . 14 5 Inspection and cleaning . 16 5.1 End face inspection . 16 5.2 Cleaning . 20 6 Scheduled maintenance and inspection . 24 6.1 When to maintain/Inspect? . 24 6.2 Maintenance/Inspection of system . 25 6.3 Maintenance/Inspection of components . 26 Annex A (normative)
Termini end face contamination . 27 Annex B (normative)
Cleaning Methods . 32 B.1 Method 1 . 32 B.2 Method 2 . 34
SIST EN 4533-004:2018



EN 4533-004:2018 (E) 3 European foreword This document (EN 4533-004:2018) 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 July 2018 and conflicting national standards shall be withdrawn at the latest by July 2018. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN shall not be held responsible for identifying any or all such patent rights. This document supersedes EN 4533-004:2006. 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. SIST EN 4533-004:2018



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Introduction a) The Handbook This handbook aims to provide general guidance for experts and non-experts alike in the area of designing, installing, and supporting fibre-optic systems on aircraft. Where appropriate more detailed sources of information are referenced throughout the text. It is arranged in 4 parts, which reflect key aspects of an optical harness life cycle, namely: Part 001: Termination methods and tools Part 002: Test and measurement Part 003: Looming and installation practices Part 004: Repair, maintenance, cleaning and inspection b) Background It is widely accepted in the aerospace industry that photonic technology significant advantages over conventional electrical hardware. These include massive signal bandwidth capacity, electrical safety, and immunity of passive fibre-optic components to the problems associated with electromagnetic interference (EMI). Significant weight savings can also be realized in comparison to electrical harnesses which may require heavy screening. To date, the EMI issue has been the critical driver for airborne fibre-optic communications systems because of the growing use of non-metallic aerostructures. However, future avionic requirements are driving bandwidth specifications from 10’s of Mbits/s into the multi-Gbits/s regime in some cases, i.e. beyond the limits of electrical interconnect technology. The properties of photonic technology can potentially be exploited to advantage in many avionic applications, such as video/sensor multiplexing, flight control signalling, electronic warfare, and entertainment systems, as well as sensor for monitoring aerostructure. The basic optical interconnect fabric or `optical harness’ is the key enabler for the successful introduction of optical technology onto commercial and military aircraft. Compared to the mature telecommunications applications, an aircraft fibre-optic system needs to operate in a hostile environment (e.g. temperature extremes, humidity, vibration, and contamination) and accommodate additional physical restrictions imposed by the airframe (e.g. harness attachments, tight bend radii requirements, and bulkhead connections). Until recently, optical harnessing technology and associated practices were insufficiently developed to be applied without large safety margins. In addition, the international standards did not adequately cover many aspects of the life cycle. The lack of accepted standards thus lead to airframe specific hardware and support. These factors collectively carried a significant cost penalty (procurement and through-life costs), that often made an optical harness less competitive than an electrical equivalent. This situation is changing with the adoption of more standardized (telecoms type) fibre types in aerospace cables and the availability of more ruggedized COTS components. These improved developments have been possible due to significant research collaboration between component and equipment manufacturers as well as the end use airframers. SIST EN 4533-004:2018



EN 4533-004:2018 (E) 5 1 Scope The handbook gives guidelines related to ‘Fault analysis and repair’ as well as ‘maintenance and inspection of fibre optic links. The first deals with what to do when something goes wrong – how to go from a fault notification to locating the fault, and finally, repairing it. The second covers the recommended procedures for upkeep and maintaining harness health over the lifetime of its installation. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 4533-001, Aerospace series — Fibre optic systems — Handbook — Part 001: Termination methods and tools EN 4533-002, Aerospace series — Fibre optic systems — Handbook — Part 002: Test and measurement EN 4533-003, Aerospace series — Fibre optic systems — Handbook — Part 003: Looming and installation practices EN 2591-601, Aerospace series — Elements of electrical and optical connection — Test methods — Part 601: Optical elements — Insertion loss EN 3733 (all parts), Aerospace series — Connector, optical, circular, single channel, coupled by self-locking ring, operating temperature up to 150 °C continuous EN 4531-101, Aerospace series — Connectors, optical, circular, single and multipin, coupled by threaded ring — Flush contacts — Part 101: Optical contact for EN 4641-100 cable – 55 °C to 125 °C — Product standard EN 4639-101, Aerospace series — Connectors, optical, rectangular, modular, multicontact, 1,25 diameter ferrule, with removable alignment sleeve holder — Part 101 : Optical contact for cable EN 4641-100 — Operating temperatures between – 65 °C and 125 °C — Product standard EN 4645 (all parts), Aerospace series — Connectors, optical, circular, single and multipin, coupled by threaded ring, self-locking 1,25 mm diameter ferrule with removable alignment sleeve holder IEC 60825-1, Safety of laser products — Part 1: Equipment classification, requirements and user's guide IEC 61300-3-35, Fibre optic interconnecting devices and passive components — Basic test and measurement procedures — Part 3-35: Examinations and measurements — Visual inspection of fibre optic connectors and fibre-stub transceivers ARINC 805, Harsh environment fibre optic connectors/testing SAE-AS5675, Characterization and requirements for new aerospace fibre optic cable assemblies — Jumpers, end face geometry, link loss measurement, and inspection SIST EN 4533-004:2018



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3 Fault analysis 3.1 Fault notification A fault notification will arise from one or more of three sources; scheduled maintenance, Built-In-Test (BIT), or failure of equipment. Ideally, scheduled maintenance should highlight all latent faults i.e. those which initially have no effect on the system performance but may lead to a problem sometime later during aircraft operation. It should also highlight faults of the gradual degradation type i.e. those which gradually deteriorate the system performance but have yet to cause a failure and any other faults that slipped through the BIT net. BIT is the ability of the aircraft’s systems to diagnose themselves. It should identify all faults that occur in the time between scheduled maintenance and, with the exception of sudden catastrophic faults, before a failure occurs. It should also be able to provide some help in locating the fault. Failure is the worst case and should only be the result of a fault occurring which cannot be prepared for. 3.2 Symptoms This is where differences between fibre optic and electrical installations become apparent. The most common symptom in a fibre optic link is complete or partial loss of optical power. This occurs when light breaks its confinement from the fibre core and can be the result of damage to the fibre or interconnect. It can also be the result of contamination of the fibre optic terminus end face, excessive pressure, crushing or severe bending on the fibre optic cable. Depending on the magnitude of the loss, the result may be a fault that is above or below the link threshold – a fault below the link threshold is a failure. Severe damage, such as an optical fibre break may induce a complete loss of optical power. Intermittent optical signals are possible and may be the result of fibre movement e.g. vibration or bending of a fibre. An increase in optical power is also possible although this is more likely to be due to stability of the light source rather than the link itself. Gradual degradation of optical power is an important symptom to be able to detect as it could indicate the onset of a failure. Increasing contamination or proliferation of damage to the fibre optic terminus end face could be responsible. Outside of the harness it could be due to degradation of an optical source. Back reflection is a phenomenon that occurs at any interface with different refractive index, e.g. glass/air. Back reflection is of particular concern where active devices utilise laser-based systems where reflected light can affect the transmitting capabilities of the optical source. This can result in degradation of the transmitted signal and potentially damage the optical source.
SIST EN 4533-004:2018



EN 4533-004:2018 (E) 7 Latent fault symptoms i.e. those which have no effect on the optical power of the system but could be the first stage of a fault that does. These are most likely to be noticed during inspection and include poor routing, incorrect retention methods leading to exertion of excessive pressure on the fibre optic cable and poor stress relief on interconnects. 3.3 Potential faults 3.3.1 Fibre Fibre breaks can occur in the cable where the fibre enters a connector and inside the connector ferrules. A broken fibre would lead to total loss of optical power or, if an optical path was maintained across the break, a reduction in power which could oscillate under vibration. Fibre breaks are most likely to occur during installation or other maintenance work when the fibre is placed under excessive stress. Latent faults such as damage to the structure of a backshell may lead to a break where the fibre is at its most vulnerable – entering the connector ferrules. Other fibre faults are cracks which may develop under environmental stress and micro-bending which is where the fibre is bent into ‘ripples’ of millimetre bend radii within the cable. This effect has been seen in telecommunication cables when exposed to cold temperatures which cause the cable jacketing to contract. Damage and contamination of the fibre end face are listed as connector faults. Another possible fibre fault can also occur, which is due to localized stress (for instance unappropriated cable-tie mounting, low bend radius, fibre crush) applied to the fibre that may induce unwanted optical attenuation. 3.3.2 Cable Physical damage to the cable can come from abrasion or clamping/crush damage. The cable also has a long and short-term minimum bend radius. If these are not adhered to, there is risk of damage to the fibre. 3.3.3 Connector The connector and the area around the connector is perhaps the most susceptible to faults. De-mating can lead to the most common problem; contamination. De-mating is discouraged as far as possible but it is unavoidable in some circumstances. Contamination can range from mild, where a wipe clean with a lint-free cloth will suffice, to severe, where the connection mechanism is affected. Contamination may lead to permanent damage of the fibre end face. Fluid contamination presents some unique problems.
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There are also issues of fibre grow in/out (when the adhesion between fibre and ferrule fails) and fibre misalignment. Connectors also have the potential to be carrying latent faults such as over-tightening of the connection mechanism and inadequate strain relief. 3.3.4 Backshell Apart from physical damage to the backshell there is also potential for fibres to be crushed, bent or strangled if the routing within the backshell is not correct. 3.3.5 Conduit Breaking, kinking or crushing of conduit could have an effect on the optical fibre but experience with electrical harnesses suggests that damage to a conduit is likely to be a latent fault which is found during scheduled maintenance before it affects harness performance. 3.3.6 Pigtailed components A break or crack of a pigtailed fibre from a component would give rise to a total or partial optical power loss symptom. 3.3.7 Splices Splice faults that could have a direct effect on the optical signal include fibre separation. Additionally, mechanical splices may be degraded by contamination, fluids ingress, migration of index matching means. Latent faults are similar to those for connectors; inadequate strain relief and support. 3.3.8 Others The faults listed above are limited in scope to the harness. Faults at the hardware interface level e.g. transceivers and controlling electronics would result in a selection of the symptoms detailed in 3.2. Potential faults are summarised in Table 1.
SIST EN 4533-004:2018



EN 4533-004:2017 (E) 9 Table 1 — Possible symptoms for optical component failure
Complete loss of optical power Drop in optical power or intermittent loss of power or gradual degradation Increase in back reflection Decrease in optical power Latent fault symptom Fibre Fibre break Fibre break Fibre crack Micro-bending Fibre break Fibre crack Fibre localized stress — Cable — Tight Bend Cable Crushed — — Cable abrasion Cable crushing Cable split Terminus Severe contamination Fibre grow in/out Fibre break inside of terminus — Fibre grow in/out Fibre misalignment — Inadequate strain relief Connector Contamination Contamination Fluid ingress — Fluid ingress (index matching) Inadequate strain relief Backshell — Fibres crushed/bent/strangled — — Physical damage Conduit — Conduit kink or crush — — Conduit break, kink or crush Coupler Pigtail break Mixer rod crack Pigtail break/Crack Mixer rod crack Pigtail break — — Splice Fibre grow in/out Packaging failure Fibre grow in/out Packaging failure
Fluid ingress Poor end face preparation Poor end face alignment — Inadequate strain relief Other Transceiver fault Transceiver fault — Transceiver fault — SIST EN 4533-004:2018



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3.4 Fault identification and location 3.4.1 General Fault finding techniques and strategies will play a key role in restoring and maintaining the integrity of aircraft fibre-optic systems. Unless appropriate solutions are available the aircraft operator could incur significant down time, cost, and inconvenience whilst the fault is being located. The problem is exasperated by the fact that the fibre-optic networks in question could be relatively complex, incorporating fan-out connection paths (enabled by passive couplers or active switches, for example) and may be harnessed into relatively inaccessible areas of the airframe. Criteria considered when assessing potential fault finding techniques included:  effectiveness of the technique for likely fault scenarios,  cost of equipment,  skill level and time required to perform the technique,  size, weight, power requirements, and robustness of equipment,  safety issues. The first factor that will influence the choice of fault location technique is the type of harness – inaccessible, embedded or open. Several of the techniques described below cannot be used on an embedded or inaccessible harness. The first step of fault identification is to determine the failed part: cable, connector or system. The following fault location methods are presented from the simplest to the most complex. 3.4.2 Good practices during maintenance/Inspection The following good practices are recommended to be included as part of any overall scheduled maintenance philosophy:  Whenever test equipment requires de-mating of a connector the appropriate cleaning procedure should be followed to ensure no contamination is introduced.  End protection must be used at all times. When de-mating is required the de-mated connectors should be protected. Dust caps should be kept clean. Disposable items are preferred.  Correct fibre handling procedures should be followed to avoid damage. Minimum bend radii should be observed. Exposed fibre should be treated as sharps.  Eye safety issues should be highlighted. Test equipment should all be eye safe and extra care needs to be taken if the system transceivers pose potential eye safety problems.  Correct sources and filters should be used for all footprinting, including O.T.D.R’s. Failure to do so will invalidate data collected. SIST EN 4533-004:2018



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3.4.3 Inspection This is the simplest fault location procedure and falls into two categories – inspection of the end faces of the fibre optic termini and external inspection of cables and connector housings (which requires no de-mating). A clean, undamaged end face is essential for optimum performance. Inspection of multi-way connectors can be complicated, especially if the termini are recessed. Visual inspection of a fibre optic bundle is the same as for existing electrical harnesses. Inspection of fibre optic bundle components (if accessible) is the only viable way to control latent faults. 3.4.4 Continuity check A continuity test performed with a simple laser source is an easy method to show a fibre or connector break. This method needs to have access to both ends of the cable. It consists in lighting one end with the laser and to check the presence of the light on the other side. Eye protections must be used during this test. 3.4.5 Power measurement Provided appropriate launch and detection conditioning is applied (see EN 4533-002), optical power measurement is the recommended technique for determining attenuation in ‘useable power’ through an avionic fibre-optic harness or harness component. If compared to a previous equivalent measurement of the system, a measurement of a control sample, or a theoretical prediction, the presence of a localised fault or distributed degradation (due to ageing, for example) in the harness can be deduced. Optical power measurement can also be used for fault location given prior knowledge that a fault has been detected, e.g. from BIT. If the symptom is ‘signal below threshold’ then the use of appropriate conditioning is still recommended. For ‘no signal’ or ‘intermittent signal’ type faults this is much less critical. In fact, a tailored overfilled or under filled launch may be advantageous in certain cases, e.g. a significant under fill may minimise non-critical loss mechanisms that would otherwise confuse/distract the operator. In some senses this case is analogous to visual fault finding (especially when used for continuity checking) except that an optical power meter is used in place of the eye. Optical power measurement is intrinsically a double ended test. Thus, whatever the symptom, in order to localise the fault or loss mechanism further, access to in-line connectors within the harness is required for the test source and/or the detector. The technique is therefore far less applicable to ‘embedded’ harnesses than to ‘open’ harnesses. By accessing in-line connectors in open harnesses and then taking appropriate optical power measurements, a fault can be localised to a particular “connectorised” section of the harness. This can then be repaired, cleaned, or replaced depending on the repair policy adopted. Having taken appropriate repair action, optical power measurement also has a role to play in confirming the level of functionality of the harness.
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To summarise, power measurement is easy to perform and interpret but is probably more time consuming than some of the others described in this report. It is the best technique for locating gradual degradation faults and drop in optical power as the data is simpler than that presented by an OTDR. However, power measurement cannot find the position of a fault on a cable so for a long run between connectors e.g. on a point-to-point link its usefulness is reduced. 3.4.6 Insertion loss measurement Insertion loss measurement is a variation of power measurement as it consists in determining the attenuation on the link. Contrary to power measurement where the measure is performed with the functional system connected to the link, insertion loss measurement needs to connect fibre ends to light launch system on one end and light detector system on the other end. It enables to quantify the attenuation of the link. The result must be compared to a reference measurement or to the theoretical insertion loss prediction of the link to identify a fault but it won’t localise the defect. The measurement method is described in EN 2591-601 standard. 3.4.7 Optical time domain reflectometry The use of an optical time domain reflectometry is a recognised method of accurately measuring the length of an optical link and identifying ‘events’ within the link. Designed for long haul, single mode optical fibres there have been doubts over their suitability for use on very short aerospace fibre optic links. New high resolution OTDR’s have been developed and are able to measure ‘events’ with centimetre resolution in multimode fibres. An event can be described as being identified losses within the link, such as; Insertion Loss (IL) (interconnects), attenuation (tight bends, fibre breaks), etc. This new capability allows operators to measure and map events in short optical links of less than 5 metres and up to 100’s of metres. An initial end to end measurement of an optical link can be taken and stored, future measurements can then be carried out from one end of the link. This allows full measurement of a link with minimal disturbance of the system. In addition, the equipment is also capable of providing IL and RL measurements across events, video inspection and visual fault location providing multi-function capability. Full details of OTDR measurement of short optical links is defined in EN 4533-002, Test and Measurement. 3.4.8 BIT information As well as signalling a fault, BIT can also play a part in fault location. In particular, some of the other techniques covered here, such as power measurement and OTDR analysis, ideally require information previously acquired from the BIT information to rationalise the number of fault possibilities.
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4 Repair techniques 4.1 General Once the fault has been isolated a repair can be initiated. Ideally the repair strategy for a specific aircraft will be such that given the fault and scenario, a single repair technique will be app
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