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MSG-2 is maintenance process oriented. The process is the means for classifying the way in which a particular component is maintained. The intent of the process is to ensure the inherent design reliability of the component is maintained. The three primary maintenance processes of MSG-2 are Hard-time, On Condition and Condition Monitoring.
MSG-2, Primary Maintenance Processes Definitions:
Hard Time (HT), Overhaul Time Limit or Part Life-Limit:This is a preventive primary maintenance process that requires a system, component, or appliance be either overhauled periodically (time limits) or removed from service (life limit). Time limits may only be adjusted based on operating experience or tests, in accordance with procedures in the operator’s approved reliability program.
On Condition (OC):This is also a preventive primary maintenance process that requires a system, component, or appliance be inspected periodically or checked against some appropriate physical standard to determine if it can continue in service. The standard ensures that the unit is removed from service before failure during normal operation. These standards may be adjusted based on operating experience or tests, as appropriate, in accordance with a carrier’s approved reliability program or maintenance manual.
Condition Monitoring (CM):This is a primary non-preventative maintenance process. Items classified in this process are permitted to fly-to-failure without a plan for removal. Therefore, safety related items are not eligible for condition monitoring classification. Items classified in the condition monitoring process do not have an adverse relationship between age and reliability.
MSG-3 is a task-oriented logic that uses a “top down” approach at looking at failure consequences.
Systems/powerplant functional failures are categorized as safety or economic, then subcategorized as hidden or evident.
Structures logic considers damage tolerant design and structural deterioration factors of fatigue, environmental, and accidental damage.
Other structure not covered in the structural program is covered in the Zonal Inspection Program.
The latest revision of MSG-3 includes logic for development of L/HIRF maintenance programs.
MSG-3 Systems/Powerplant Maintenance Task Definitions:
Lubrication/Servicing (LU/SV): Any act of lubrication or servicing for the purpose of maintaining inherent design capabilities. The replenishment of the consumable must reduce the rate of functional deterioration.
Operational/Visual check (OP/VC): Hidden functional failure categories. An operational check is a task to determine if an item is fulfilling its intended purpose. The check does not require quantitative tolerances, but is a failure-finding task. A visual check is an observation to determine that an item is fulfilling its intended purpose and does not require quantitative tolerances. This is a failure finding task that ensures an adequate availability of the hidden function, to reduce the risk of a multiple safety failures, and to avoid economic effects of multiple failures and be cost-effective.
Inspection/Functional check (IN/FC), all categories.
Inspections:
Detailed inspection: An intensive visual examination of a specific item, installation or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at an intensity deemed appropriate. Inspection aids such as mirrors, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required.
General visual inspection: A visual examination of an interior or exterior area, installation, or assembly to detect obvious damage, failure or irregularity. This level of inspection is made from within touching distance, unless otherwise specified. A mirror may be necessary to ensure visual access to all surfaces in the inspection area. This level of inspection is made under normally available lighting conditions, such as daylight, hangar lighting, flashlight, or drop-light and may require removal or opening of access panels or doors. Stands, ladders, or platforms may be required to gain proximity to the area being checked.
Special detailed inspection: An intensive examination of a specific item, installation, or assembly to detect damage, failure or irregularity. The examination is likely to make extensive use of specialized inspection techniques and/or equipment. Intricate cleaning and substantial access or disassembly procedures may be required.
Functional check: A quantitative check to determine if one or more functions of an item perform within specified limits. Reduced resistance to failure must be detectable, and there must be a reasonably consistent interval between a deterioration condition and functional failure.
Restoration (RS): That work necessary to return an item to a specific standard. Since restoration may vary from cleaning or replacement of single parts to a complete overhaul, the scope of each assigned restoration task has to be specified.
Discard (DS): The removal from service of an item at a specified life limit. Discard tasks are normally applied to so-called single celled parts such as cartridges, canisters, cylinders, engine disks, safe-life structural members, etc.
MSG-3 Structural Inspection Program: Aircraft structural programs use an analysis to assess each structural item in terms of its significance to continuing airworthiness, susceptibility to any form of damage, and the degree of difficulty involved in detecting such damage. Once this is established, scheduled inspections can be developed which can be shown to be effective in detecting and preventing structural degradation due to each of the deterioration factors of fatigue, environmental deterioration, or accidental damage.
MSG-3 Zonal Inspection Program: Zonal inspections may be developed from application of the zonal analysis procedure. This requires a summary review of each zone on the aircraft and normally occurs as the MSG-3 analyses of structures, systems, and powerplants are being concluded. Many support items such as plumbing, ducting, other structure (non significant structure), wiring, etc., may benefit from a general visual inspection to detect degradation.
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