Maintainability Programs
Maintainability Assessment
Maintainability Modeling
Maintainability Demo
Design for Maintainability
DRACAS

At the onset of a program it is important to identify the maintenance concept and derive the initial system maintainability requirements and design attributes. A maintainability assessment of a system or equipment is one method used to determine and validate the actual design taking into consideration the maintainability characteristics of the system. This could include performing an assessment of the:

• Quantitative characteristics
• Physical Characteristics

Quantitative characteristics: The quantitative characteristics that could be considered for a system, are it's specific maintainability performance characteristics and could include:

Mean-Time-To-Repair: ( MTTR): The MTTR would be calculated taking into consideration the times needed to implement each of the corrective maintenance and preventative maintenance task for the system for each level of maintenance. (See Maintainability Modeling)

Maximum Time to Repair: An important element of the quantitative characteristics is the max time to repair.

Built-In-Test (BIT): The establishment of the BIT capability is important. For example a system (mainly electronic) the principal means of fault detection and isolation to the LRU level requires the use of self-diagnostics or built-in-test. This capability, in terms of its effectiveness may need to be quantified.

Heath Status and Monitoring (HSM): Incorporated into the design of the system could be a HSM capability. This could be a relatively simple concept, such as the monitoring of the axle temperature of a locomotive to safeguard against the main wheel bearing overheating. Other HSM systems may employ an arsenal of sensors, such as strain gages, thermal sensors, accelerometers etc. to measure electrical and mechanical stresses on a system. However, to determine the effectiveness of this approach needs to be established in quantitative terms.

Physical Characteristics: The physical characteristics take in consideration the issues such as accessibility and the characteristics that will accommodate the maintainer's for ease of maintenance, and include:

Ergonomics: These characteristics would address the physical characteristics for the maintainer. MIL-STD-1472D Human Engineering Design Criteria for Military Systems, Equipment and Facilities, and MIL-STD-46855B Human Engineering Requirements for Military Systems, Equipment and Facilities provide good source when considering issues associated with human factors. This would range from the weight of components and required lifting points to the clearance between electrical connectors etc.

Mechanical Interfaces: May require specific criteria for interface issues such as mating and self-alignment, captive fasteners, access for tools, to keyed connectors.

Test Point: This effort must be interfaced with the testability engineering effort. A system may require some manual diagnostic interaction, where specific test points will be required for fault diagnostic and isolation purposes.

Test Equipment: This assessment would address how test equipment (and tools) would interface with the system or equipment.

Accessibility: Is an important attribute. As a system integrator the design of a system must avoid the need to remove other assemblies to gain access to a failed unit or the ability to permit the use of standard hand tools must be observed.

Reliability degradation: Caution must be given to reliability characteristics. A system required to provide a continuous service, by utilizing redundant elements should be safeguarded against any maintenance actions. For example to remove and replace a failed unit would not allow the complete system to be powered down.

Software Characteristics: With systems using software applications to perform their functions, such as a real-time data processing platform, it must be recognized that these, if required because of a maintenance action, to be powered down, would need time to reboot the system and retrieve any back-up configuration and database files.

When assessing the maintainability characteristics, the maintenance concept must play an influential role. For example to stipulate that a system should be capable to isolate to a function level of each circuit card assembly, may not be justified if the circuit card, through the Logistics Support Analysis process deemed it to be returned to an third party for repair or even discarded. These could otherwise impose unnecessary developmental cost for a redundant feature.

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