MAINTAINABILITY DESIGN TECHNIQUES METRIC - AcqNotes.com

Downloaded from http://www.everyspec.com on 2011-10-29T14:56:01.DOD-HDBK-791(AM)gram within the North Atlantic Treaty Organization(NATO), which is discussed in par. 3-2.2. The US Alliesusually employ the International System of Units (SI),i.e., metric units. Even though DoD Directive No.4120.18 (Ref. 3) established a policy to consider the use ofthe metric system in all of its activities consistent withoperational, economical, technical, and safety requirements.materiel fielded prior to 1976 is still in the US andNATO inventories and new equipment being fielded isstill not metric. Ref. 4 presents a thorough discussion ofthe SI system and contains a comprehensive list of conversionfactors for transferring from one system to theother. Software programs are available to facilitate theconversion.3-3.2 RATIONALIZATION, STANDARDIZA-TION, AND INTEROPERABILITY (RSI)PROGRAMThe RSI Program was established by DoD DirectiveNo. 2010.6 (Ref. 5). The overall objective of the programwas to achieve improved NATO operational effectivenessand combat capability by means of1. Rationalization. Any action that increases theeffectiveness of NATO forces through more efficient oreffective use of defense resources committed to NATO,including both codevelopment and coproduction of NATOStandard Weapon systems2. Standardization. The process by which nationsachieve the closest practicable cooperation among forces;the most efficient use of research, development, and productionresources: and agreement to adopt on thebroadest possible base the use of common or compatibleprocedures. equipment, and tactical doctrine3. Interoperability. The ability of systems, units, orforces to provide services to, and accept services from,other systems. units, or forces and to use the services soexchanged to enable them to operate effectively together.Standardization if and when ever attained wouldensure a major increase in the operational capability ofNATO forces. Total standardization within NATO wouldovercome the present advantage of the Warsaw Pactforces in that their weapons and support systems areessentially standard throughout the Pact. The forces ofthe Pact countries currently possess a high degree ofstandardization because of the unique situation that limitstheir source of’ weapons, ammunition, and follow-onsupplies.It is interesting to note that the National CodificationBureau Code (NCBC) identifies 24 allied country codesstored in the Defense Logistics Services Center (DLSC)(Ref. 6); this fact indicates that standardization is emergingeven though it may be limited to such items as tiresand storage batteries. The national stock number, ofwhich NCBC and DLSC are an integral part, is discussedin par. 3-5.3-3.3 DESIGN PRINCIPLESTo attain rnaximum interchangeability, the followingdesign principles apply:1. Functional interchangeability of’ parts and unitsshould exist wherever physical interchangeability existsto avoid a dangerous situation.2. Physical interchangeability should not exist wheneverfunctional interchangeability is not intended.3. Whenever complete functional and physical—interchangeability is impractical, the parts and unitsshould be designed for functional interchangeability, andadapters provided to make physical interchange possible.4. To remove latent doubts, sufficient informationshould be provided undocumented instructions and identificationplates to enable the technician to decide positivelywhether or not two similar parts or units are actuallyinterchangeable.5. Differences should be avoided in the shape, size,mounting, and other physical characteristics of functionallyinterchangeable units.6. Modifications of parts and units should notchange the manner of mounting, connecting, and otherwiseincorporating them into an assembly or system.7. Complete interchangeability should be providedfor all parts and units thata. Are intended to be identicalb. Are identified as being identicalc. Have the same manufacturer’s part number orother identificationd. Have the same function in different applications—this is especially important for parts and units that have ahigh failure rate.8. Parts, fasteners and connectors, lines and cables,etc., should be standardized throughout a system, particularlyfrom unit to unit within the system.9. Mounting holes and brackets should be made toaccommodate parts and units made by different facilities—i.e., make them universally interchangeable.3-3.4 ADVANTAGESThe advantages to be gained from effective interchangeabilityare essentially the same as those gained by standardization(see par. 3-2.2). In addition, the provision ofinterchangeability is essential to effective standardization.The greatest advantage is gained when parts are bothstandardized and interchangeable.3-4 DESIGN APPLICATIONSAreas that are well suited to standardization and interchangeabilityinclude operating and physical characteristics,as well as equipment types. Standard parts, components,circuits, methods, and practices should be used inthe following applications:1. Voltage and/or current levels, input or output,3-3