2. PRINCIPIOS BÁSICOS DE LOS OBJETIVOS DE DESARROLLO
2.1 Antecedentes de los Objetivos del Desarrollo Sostenible (ODS)
Due to the increased complexity of modern aircraft, the amount of information needed, within the Maintenance, Spares and Repair manuals, has grown to an enormous extent.
For example, the Maintenance manuals, for one modern aircraft alone, consist of twenty volumes, each of which would be more than 76 mm (3 in) thick.
To compress even greater amounts of data, other media are utilised, to make the information more easily available to aircraft servicing technicians. These include: • Microfilm
• Microfiche
• Computers (CD-ROM). 5.5.1 Microfilm
This method entails one publication being reproduced, on a roll of film and contained in a special cartridge case, approximately three inches (76 mm) square. The pages are sequentially copied onto the film and wound upon a drum, within the cartridge case.
A microfilm ‘Reader’ (a projector) is used, to wind the film through a ‘gate’ and display a single page of text/drawing upon a screen, which is large enough to enable the text and illustrations to be read and understood.
Because of the condensing of the ‘hard copy’ books into a small space; a complete set of maintenance manuals can, thus, be contained in a small number of microfilm cartridges which can be stored close to the Reader.
A number of these projectors are provided with a printing facility, that allows the person, reading the film, to print a copy of any sheets which contain information that is required away from the machine. All copies, removed from the microfilm reading room, must be used once only, and not retained for later work. This practise ensures that amendments and updates are not missed.
5.5.2 Microfiche
A similar process to microfilm, with the exception that many pages of the manuals are reproduced on one clear sheet of film, measuring approximately 100 mm x 150 mm (4 in x 6 in). Each sheet is capable of storing a large number of pages (over 100) of text/drawings and takes up very little space.
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
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engineering
The Reader is similar to the microfilm Reader except that the film slide is moved about, beneath the viewing lens, until the relevant page appears upon the screen. By simply pressing a button on the machine, a photocopy of the page being viewed can be produced for remote use and, once again, any copies should not be retained for future use.
Amendment of both this and the microfilm system is by direct replacement, with local disposal of the unwanted items.
5.5.3 Computer CD-ROM
The use of computers, with respect to aircraft maintenance manuals, (and other publications), has the primary advantage of the huge amount of information that can be stored on one Compact Disc (CD).
A single computer, located within a maintenance facility, could have all the necessary publications (such as the Maintenance Manual, Illustrated Parts Catalogue and Wiring Diagrams), for the relevant aircraft type, held on one CD. As with the other two systems, there should be the facility to print the necessary information required with, of course, the limitation that the information is only valid ‘on-the-day’, and must not be used for repetitive jobs.
Updating of computer-based systems is by the simple replacement of the relevant CD-ROM, although there may be intermediate amendments.
5.5.4 Supplementary Information
It is important that only the current issue, of whichever system is in use, is supplied to servicing technicians. This means that the amendment procedures must be carefully monitored (and especially the disposal of the out-dated material). The new amendments come with a ‘Letter of Transmittal’, from the relevant authority, in exactly the same manner as they do with the ‘hard copy’ technical publications.
Because of the need to dispose of large amounts of information, whenever even a minor update or amendment is carried out, it is normal to produce Supplementary Information in hard copy form, as an intermediate source of current information. These issues are in addition to either the film/fiche/CD-ROM systems in use and must be not only carefully monitored, but also well publicised. This ensures that the technicians know that the information, contained in the system they are using, could, possibly, contain small items of out-of-date information.
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
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5.6 AERONAUTICAL STANDARDSA standard is variously defined as:
• Something, established for use as a rule, or basis of comparison, in measuring or judging capacity, quantity, content, extent, value or quality, or a level or grade of excellence
• Any measure of extent, quality or value, established either by law, or by general use, or by consent.
In the normal performance of their duties, technicians can find a wide array of standards, establishing the characteristics of the materials and components that they encounter in their day-to-day work of maintaining and repairing aircraft. 5.6.1 Air Transport Association Specification No. 100
Since 1 June 1956, the Air Transport Association of America (ATA), has used a specification, to establish a standard for the presentation of technical data, by aircraft, engine or component manufacturers, that is required for their respective products.
This specification is known as ATA Specification No.100 (ATA 100), and its two Chapters clarify the general requirements of the aircraft industry, with reference to the coverage, preparation and organisation of all technical data.
Chapter 2 of the ATA 100 covers policies and standards applicable to specific manuals and it details the names and contents of the various manuals that must be prepared by the manufacturer. Such manuals include the:
• Aircraft Maintenance Manual • Wiring Diagrams
• Structural Repair Manual
• Aircraft Illustrated Parts Catalogue • Component Maintenance Manual • Illustrated Tool and Equipment Manual • Service Bulletins
• Weight and Balance Manual • Non-Destructive Testing Manual • Power Plant Build-up Manual • Aircraft Recovery Manual
• Fault Reporting and Fault Isolation Manuals • Engine Manual
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Chapter 1 of the ATA 100 covers policies and standards applicable to all publications and provides a uniform method for arranging technical material, within the relevant publications, in an effort to simplify the technician’s problem in locating instructions and parts.
In the ‘Arrangement of Material’ section, in Chapter 1 (1-2) of the ATA 100, the standard details the use of a three-element identifier number. Each element of the identifying number consists of two digits. The first element is designed to provide identification of all topics or systems, within the respective manuals, by reference to specific Chapters. The second element identifies sub-systems (sub- topics) as Sections, while the third element identifies associated sub-sub-systems (sub-sub topics) as Subjects.
Table 4 illustrates an example of how the ATA 100 numbering system (in this instance using numbers ranging from 27-00-00 to 27-31-14) is used, to identify the material which is covered at particular locations within a typical Maintenance Manual.
Table 4
EXAMPLE OF ATA 100 NUMBERING SYSTEM First Element, Chapter (system) Second Element, Section (sub-system) Third Element, Subject (unit) Coverage
27 00 00 Material which is applicable to
the system as a whole (in this instance Flight Controls).
27 31 00 Material which is applicable to
the sub-system as a whole (in this instance Elevator and Tab Control System).
27 31 00 Material which is applicable to
the sub-sub-system as a whole. This number (digit) is assigned by the manufacturer.
27 31 14 Material applicable to a specific
unit of the sub-sub-system (Elevator Feel Computer). Both digits are assigned by the manufacturer
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
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The subject is broken down yet further – into Page Blocks – to provide maintenance personnel with more detailed information on specific topics (or sub- topics) which relate to the Subject material.
Table 5 shows an example of a Page Block system along with the topics and sub- topics, which are allocated to the relevant Page Block numbers.
Table 5
EXAMPLE OF ATA 100 PAGE BLOCK NUMBERING SYSTEM
Topic or sub-topic Page Block
Description and Operation 1 to 100
Trouble-shooting 101 to 200
Maintenance Practices (if brief) 201 to 300
(Otherwise) Servicing 301 to 400 Removal/Installation 401 to 500 Adjustment/Test 501 to 600 Inspection/Check 601 to 700 Cleaning/Painting 701 to 800 Approved Repairs 801 to 900
Note: The word EFFECTIVITY - which may appear on the left hand side of the bottom of a page – is used to identify the aircraft serial number, or manufacturer’s serial number (MSN), or aircraft model to which a particular Subject topic may refer and those numbers will be shown. If the word ALL appears adjacent to the EFFECTIVITY then the information concerns all types of aircraft (or components), regardless of any serial numbers.
Chapter 1 of the ATA 100 also details the policies and standards applicable to all publications with reference to the:
• Physical Requirements: Format of media (Paper, Film, Page layout/numbering etc.) and Indexing (List of Effective Pages [LEPs], Table of Contents [TOC], Text, Divider Cards, Sequence, etc.)
• Issuance and Revision Service
• Aircraft and Engine Zoning: Access Door, Port, Panel and Area identification. Many airlines and similar companies also organise their spare parts in stores departments under the relevant ATA specification numbers and, irrespective of the aircraft type, information on similar components will be found in the same Chapter and Section. A complete table of the ATA numbering system, sub- system and titles, allows the technician to establish, precisely, where the information required can be found in the respective manuals.
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5.6.2 International Organisation for Standardisation (ISO)
This is an international organisation, which has representatives from each member country, usually consisting of that country’s own standardising organisation.
5.6.3 British Standards (BS)
These are controlled by the British Standards Institution (BSI) and are the
recognised body for the preparation and promulgation of national standards and codes of practice. The BSI represents the United Kingdom on matters pertaining to ISO.
5.6.4 Military Standard (MS)
This standard was developed by the military, and has found its way into all aspects of aviation. The MS (also MIL) standard has, all but, replaced the AN system and, in many cases, former AN parts are now being produced as MS or MIL parts.
The suffix usually consists of a letter, which identifies the item (R for rivet, S for steel, C for cable, etc.), and a serial number. These standards apply both to hardware and materials. For example, MIL-C-5424 is a standard 7 x 19, aircraft cable, made of carbon steel.
5.6.5 Air Force and Navy (AN)
The AN system is one of the most widely used standards in aircraft hardware. It was developed, together with the MS system, by the US military to ensure quality and uniformity. Items manufactured to this standard are not limited to the military and are found in all classifications of aircraft.
5.6.6 National Aerospace Standard (NAS)
Items of hardware used within military aviation, which have been proven satisfactory by the aerospace industry, can be granted a NAS designation.
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6
FITS AND CLEARANCES
For ease of manufacture and replacement, it is essential that the components of similar mechanisms should be interchangeable. For this reason limits (tolerances and allowances) are imposed on the manufacturing procedures.
The limits on dimensions ensure that, if any two mating parts are manufactured to the tolerances and allowances, stated on the drawing, then they will assemble without the need of further hand working or machining to achieve the required standard of fit.
Because shafts are much easier than holes to machine small diameters, the main systems of Limits and Fits, for engineering purposes, is usually the ‘hole-based’ system. The holes are created to a certain tolerance and the sizes of the shafts are altered to provide the required class of fit between the two items.
6.1 DIMENSIONS
Mass production has long been the basis of the approach to the most economic methods of manufacturing and the complete replacement of a defective item is common practice in the maintenance of aircraft and aerospace components. For this reason, limits are imposed on the manufacturing processes, to ensure that, if any two mating parts are manufactured to the dimensions as stated on the relevant drawings, then the parts will assemble without need of further major adjustments and in the least time possible.
The limits are based on the allowances and tolerances imposed on the dimensions of the manufactured parts. These dimensions will be given the accuracy required by the designer of the respective parts.
6.1.1 Allowances
An allowance is a difference in dimension that is necessary to give a particular ‘class of fit’ between two parts. If, for example (and using a typical limit system), a shaft were required to locate with a corresponding hole in a component. Then, to assist in the economy of manufacture, either the hole or the shaft is made as accurately as possible to the nominal size and an allowance is applied to the associated item. The term ‘shaft’ also includes bolts and pins.
If the shaft is constant and the hole varies in size, then the system used is said to be ‘shaft-based’. If the hole is constant and the shaft varies in size, then the system is ‘hole based’. The hole-based system is the one in more general use.
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The item dimensioned to include the allowance also has high and low limits and, therefore, a tolerance. The correct allowance would be the difference between the high limit of the shaft and the low limit of the hole.
6.1.2 Tolerances
The tolerance on a dimension is the variation tolerated and may be considered as a numerical expression of the desired quality of workmanship. It is the difference between the high and low limits of size for that dimension (refer to Fig. 1). Thus, a part that should be exactly 25 mm nominal diameter, will be accepted for a certain purpose if it is within the limits 25.1 mm, (the high limit); and 24.9 mm, (the low limit). The difference between the two (0.2 mm) is the tolerance.
High limit of shaft Low limit of shaft Low limit of hole High limit of hole
Shaft/Hole Tolerance Terms Fig. 1
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Table 1 shows that tolerances may be stated in one of three ways, using a hole that has a nominal size of 100 mm diameter and a tolerance of 0.02 mm as an example. Table 1 TYPES OF TOLERANCES Bilateral 100 mm ± 0.01 mm Unilateral 100 mm + 0.02 mm 100 mm – 0.00 mm Limits 100.01 mm 99.99 mm
With sheet material, such as patch plates, used in certain repairs, the dimensions quoted in the repair scheme usually have a tolerance in one direction only, the nominal size being the lower limit. In effect the patch plate must never be below the nominal size, although it can be slightly over, in accordance with the repair scheme in the manual.