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MSG-3 (Maintenance Steering Group) ‘Operator/Manufacturer Scheduled Maintenance Development’ is a document developed by the Air Transport Association (ATA) of America and it aims to present a methodology to be used for developing scheduled maintenance tasks and intervals, which will be acceptable to the regulatory authorities, the operators and the manufacturers. The main idea behind this concept is to recognise the inherent reliability of aircraft systems and components, avoid unnecessary maintenance tasks and achieve increased efficiency.
MSG-3 is widely used to develop initial maintenance requirements for modern commercial aircraft in other words Maintenance Review Board Report (MRBR) and it includes four main sections:
- ‘Systems and Powerplant’ (including components and APU’s),
- ‘Aircraft Structures’,
- ‘Zonal Inspections’ and
- ‘Lightning/High Intensity Radio Frequency (L/HIRF)’.
Each section contains its own methodology and specific decision logic diagram. Particularly ‘Systems & Powerplant’ section requires the identification of Maintenance Significant Items (MSI) before the application of logic diagrams to determine the maintenance tasks and intervals. In addition to these tasks developed by using MSG-3 analysis, other maintenance tasks may be identified as part of the certification process, which requires ‘System Safety Assessment (SSA)’ and use of methods such as ‘Failure Modes and Effect Analysis (FMEA)’ (FAR/CS 1309). Such tasks are called ‘Certification of Maintenance Requirements (CMR)’. Similarly, “Aircraft Structures’ section describes the Structure Significant Items (SSI), which are different than Principal Structure Element PSE) (FAR/CS 25.571) and it also provides methods and logic diagrams, which are to be used for the development of structural inspections tasks.
MSG-1 was first published in 1968 and used for developing scheduled maintenance for B747. Subsequently MSG-2 was developed and used for developing scheduled maintenance for 1970’s aircraft such as L1011 and DC-10. MSG-2 was process orientated and used a bottom-up approach. It also introduced ‘condition monitored maintenance’ concept. At the same time ‘European Maintenance System Guide (EMSG)’, which was an improved version of MSG-2 particularly on structure and zonal analysis, was used for development of the MRBR for the Concorde SST and completed in 1975. Based on the experience and the identified weaknesses of MSG-2, the Original version of MSG-3 was first published in 1980 and it introduced a top-down approach by focusing on ‘consequences of failure’. MSG-3 expected the assessment of functional failures and assigning consequences of failures in two basic categories, ‘SAFETY’ and ‘ECONOMIC’. MSG3 is a task orientated as opposed to MSG-2 and this eliminated the confusion associated with the different interpretations of ‘Condition Monitoring’, ‘On-condition’ and ‘Hard time’. The other fundamental improvement was the recognition of ‘damage tolerance rules’ and the ‘supplemental inspection programmes’. Since 1980, a number of revisions (Rev.1, Rev. 2, Rev. 2001, Rev. 2003, Rev. 2005, Rev. 2007) have been made to MSG-3, the most recent in 2009 but, as yet, ‘MSG-4’ has not followed. The latest version of MSG-3 introduced some elements related to Structural Health Monitoring Systems (SHMS), which was the result of issue papers published by the International Maintenance Review Board Policy Board (IMRBPB) .