1、AECMA STANDARD NORME AECMA AECMA NORM prEN 4533-004 Edition P 1 April 2005 PUBLISHED BY THE EUROPEAN ASSOCIATION OF AEROSPACE INDUSTRIES - STANDARDIZATION Gulledelle 94 - B-1200 Brussels - Tel. + 32 2 775 8110 - Fax. + 32 2 775 8111 - www.aecma-stan.orgICS: 49.060 Descriptors: ENGLISH VERSION Aerosp
2、ace series Fibre optic systems Handbook Part 004: Repair, maintenance and inspection Srie arospatiale Systmes des fibres optiques Manuel dutilisation Partie 004 : Rparation, maintenance et contrle Luft- und Raumfahrt Faseroptische Systemtechnik Handbuch Teil 004: Reparatur und Inspektion This “Aeros
3、pace Series“ Prestandard has been drawn up under the responsibility of AECMA-STAN (The European Association of Aerospace Industries - Standardization). It is published for the needs of the European Aerospace Industry. It has been technically approved by the experts of the concerned Domain following
4、member comments. Subsequent to the publication of this Prestandard, the technical content shall not be changed to an extent that interchangeability is affected, physically or functionally, without re-identification of the standard. After examination and review by users and formal agreement of AECMA-
5、STAN, it will be submitted as a draft European Standard (prEN) to CEN (European Committee for Standardization) for formal vote and transformation to full European Standard (EN). The CEN national members have then to implement the EN at national level by giving the EN the status of a national standar
6、d and by withdrawing any national standards conflicting with the EN. Edition approved for publication 30 April 2005 Comments should be sent within six months after the date of publication to AECMA-STAN Electrical Domain Copyright 2005 by AECMA-STAN Copyright Association Europeene des Constructeurs d
7、e Materiel Aerospatial Provided by IHS under license with AECMANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Page 2 prEN 4533-004:2005Foreword This standard was reviewed by the Domain Technical Coordinator of AECMA-STANs Electrical Domain. After inquiries and vot
8、es carried out in accordance with the rules of AECMA-STAN defined in AECMA-STANs General Process Manual, this standard has received approval for Publication. Contents Page Foreword 3 1 Scope 4 2 Normative references. 4 3 Fault analysis and repair 4 3.1 From notification to repair 4 3.2 Fault notific
9、ation 4 3.3 Symptoms . 5 3.4 Fault location. 5 3.5 Potential faults. 10 3.6 Repair techniques 13 4 Scheduled maintenance and inspection 16 4.1 When to maintain / inspect?. 16 4.2 Maintenance/Inspection of system. 17 5 Good practices during maintenance / inspection 18 6 Harness design considerations
10、. 19 Copyright Association Europeene des Constructeurs de Materiel Aerospatial Provided by IHS under license with AECMANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Page 3 prEN 4533-004:2005Foreword a) The handbook The handbook draws on the work of the Fibre-Opti
11、c Harness Study, part sponsored by the United Kingdoms Department of Trade and Industry, plus other relevant sources. It aims to provide general guidance for experts and non-experts alike in the area of designing, installing, and supporting multi-mode fibre-optic systems on aircraft. Where appropria
12、te 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: Rep
13、air, maintenance and inspection b) Background It is widely accepted in the aerospace industry that photonic technology offers a number of significant advantages over conventional electrical hardware. These include massive signal bandwidth capacity, electrical safety, and immunity of passive fibre-op
14、tic components to the problems associated with electromagnetic interference (EMI). To date, the latter 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 sp
15、ecifications from 10s 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
16、signalling, electronic warfare, and entertainment systems, as well as in sensing many of the physical phenomena on-board aircraft. The basic optical interconnect fabric or optical harness is the key enabler for the successful introduction of optical technology onto commercial and military aircraft.
17、Compared to the mature telecommunications applications, an aircraft fibre-optic system needs to operate in a hostile environment (e.g. temperature extremes, humidity, vibrations, and contamination) and accommodate additional physical restrictions imposed by the airframe (e.g. harness attachments, ti
18、ght 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. T
19、he 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. c) The fibre-optic harness study T
20、he Fibre-Optic Harness Study concentrated on developing techniques, guidelines, and standards associated with the through-life support of current generation fibre-optic harnesses applied in civil and military airframes (fixed and rotary wing). Some aspects of optical system design were also investig
21、ated. This programme has been largely successful. Guidelines and standards based primarily on harness study work are beginning to emerge through a number of standards bodies. Because of the aspects covered in the handbook, European prime contractors are in a much better position to utilise and suppo
22、rt available fibre optic technology. Copyright Association Europeene des Constructeurs de Materiel Aerospatial Provided by IHS under license with AECMANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Page 4 prEN 4533-004:20051 Scope The original task headings in the
23、 Fibre Optic Harness Study were Inspection and Fault Analysis and Repair and Maintenance. However, to create a more coherent and readable handbook these have been re-arranged in this part of EN 4533 to make two new topic headings Fault analysis and repair and Scheduled maintenance and inspection. Th
24、e 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. It is beneficial to read both se
25、ctions together as many of the practices and techniques are applicable to both situations. Two supplemental sections consider designing a harness with repair and maintenance in mind and good practices when maintaining or repairing a harness. To keep the handbook to a reasonable size, other Harness S
26、tudy reports are called up where more detail is required. This handbook does not contain sufficient information, for example, to be the sole reference for harness fault finding but it should provide adequate background for somebody working in that field. 2 Normative references The following referenc
27、ed 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 4533-002, Aerospace series Fibre optic systems Handbook Part 002: Te
28、st and measurement. 1)3 Fault analysis and repair 3.1 From notification to repair Once notified of a fault, choosing a repair strategy depends on a multitude of factors; accessibility of the fault, criticality of the system, availability of spares etc. These same issues already exist for electrical
29、harnesses for which proven strategies are in place. What the Harness Study set out to provide were similar strategies taking into account the unique aspects of fibre optic harnesses. The result is the “Repair and Maintenance Strategy” which contains a comprehensive list of fibre optic harness faults
30、, their symptoms and how to locate and repair them. Much of the information in this section is taken from that document. 3.2 Fault notification A fault notification will arise from one or more of three sources; scheduled maintenance, Built-In-Test (BIT), or failure of equipment dependent upon the ha
31、rness. 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
32、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 aircrafts systems to diagnose themselves. It should identify all faults that occur in the time between scheduled maintenance and, with the exception of
33、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. 1) Published as AECMA Prestandard at the date of publication of this stan
34、dard. Copyright Association Europeene des Constructeurs de Materiel Aerospatial Provided by IHS under license with AECMANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Page 5 prEN 4533-004:20053.3 Symptoms This is where differences between fibre optic and electrica
35、l harnesses become apparent. The most common symptom in a fibre optic harness 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 connector. It can also be the result of contamination, excessi
36、ve pressure on the cable or bending of the 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 a fibre break may induce a complete loss of optical power. Intermittent
37、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 harness itself. Gradual degradation of optical power is an
38、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 could be responsible. Outside of the harness it could be due to degradation of an optical source. Back reflection occurs at any interface with differen
39、t refractive index, e.g. glass/air. Connectors are designed to minimise back reflection but a fault in this area can lead to an increase. Back reflection is of particular worry in laser-based systems where the returning light can damage the optical source. A final category of symptoms are latent fau
40、lt 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 chafing of cables and poor stress relief on connectors. 3.4 Fault location 3.4.1 General Fault finding t
41、echniques 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 exas
42、perated 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
43、potential fault finding techniques included: effectiveness of the technique for likely fault scenarios; 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 locat
44、ion 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. 3.4.2 Inspection This is the simplest fault location procedure and falls into two categories inspection of the fibre end faces and ins
45、pection of the cables and connector housings (which requires no de-mating). Visual inspection of the fibre end face with the naked eye or with the aid of a microscope is an important fault finding technique. A clean, undamaged end face is essential for optimum performance. Assuming the termination e
46、nd face can be visually accessed, then inspection is, in most situations, entirely adequate for determining levels of contamination and damage. In terms of skill levels and equipment required, it is a technique suitable for all fault finding scenarios from manufacturing through to first line mainten
47、ance. An inspection microscope with a magnification of 200 is sufficient for multimode fibres. Copyright Association Europeene des Constructeurs de Materiel Aerospatial Provided by IHS under license with AECMANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Page 6 p
48、rEN 4533-004:2005Inspection of multi-way connectors can be more complicated, especially if the end faces are recessed. Most inspection microscopes are designed solely for viewing single terminations but modified microscopes which are able to hold and view multi-way connectors are appearing. Some mul
49、ti-way connectors can be partially de-assembled to provide better access to the end faces. This is beneficial for cleaning procedures as well as inspection. This is discussed further in the introduction to this Part. Visual inspection of the harness construction is the same as for existing electrical harnesses. The only difference is that often fibre has a greater minimum bend radius than most electrical cabling so inspe
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