MAINTAINABILITY DESIGN TECHNIQUES METRIC - AcqNotes.com

Downloaded from http://www.everyspec.com on 2011-10-29T14:56:01.DOD-HDBK-791(AM)Figure 4-6. Methods of Securing Hinged Covers4-4 LOCATION OF ACCESSESIt is important to consider tactical scenarios whenlocating components and the access to these components.For example, the loading of ordnance and other missionessentialconsumables must be rapid, and the readiness ofmission-essential components must be checked beforegoing into action. Accordingly, access for these essentialoperations must be accorded first priority; however, thesesame accesses can often accommodate maintenance operations.Also, existence of an access door through which toapproach an item that may require maintenance is anecessary, but not sufficient, condition to assure ease ofmaintainability—the arrangement of the componentsbehind the opening also is an important consideration(see par. 4-4.1). Thus a mutual relationship exists betweenthe access and the positioning of the components to beaccessed.Where possible, accesses should be located1. Only on equipment faces that are accessible asnormally installed2. For direct access and maximum convenience forjob procedures, i.e., arrangement3. On the same face of the equipment as relateddisplays, controls, test points, cables, etc.4. Away from high voltages or dangerous movingparts. If this is impossible, provide adequate insulation,shielding, barriers, etc., around such parts so personnelwill not be injured. These factors should be considered inthe system safety plan (Ref. 2).5. To enable heavy items to be pulled out rather thanlifted out6. To accommodate items requiring frequent adjustmentor maintenance7. So that components behind the access will not beexposed to dripping oil or other fluids, or other contaminantsgenerated by the equipment8. To avoid frames, bulkheads, brackets, and structuralmembers which will interfere with maintenance andoperations personnel’s reaching components which theymust maintain, inspect, or operate (Fig. 4-7) (Ref. 3).These general principles are expanded upon in the discussionthat follows.Figure 4-7. Avoidance of StructuralMembers (Ref. 3)4-4.1 COMPONENT ARRANGEMENTThe relative position of units which can be expectedto require maintenance inside a box-like enclosureaffects the amount of time required to perform the maintenancetask. Consider the four possible mounting positions--i.e., top. bottom, side, or back panel:1. Top Panel. In this position, quick access requiresthat the panela. Be hinged in backb. Have sufficient space above the box to swingthe panel open and to manipulate the item after openingthe box (Fig. 4-8 (A)) (Ref. 3).4-6