March 30, 2015


The MSG Process introduced a decision logic into the assessment of appropriate maintenance.

With the introduction of MSG-3 this process was refined to ensure the correct treatment of both ‚ÄúSafety Related‚ÄĚ and ‚ÄúEconomic Related‚ÄĚ as well as including the Corrosion Protection Corrosion Prevention CPCP and Structural Integrity Program considerations including:

  • Consequences of failure approach – either safety or economics
  • Distinction between failure evident to or hidden from operating crew
  • Customised task selection in each category
  • Develops an applicability and effectiveness criteria for each task
  • Task selection arranged in preferred task sequence


In the case of Airframe Structures the logic requires assessment of the possibility of structural deterioration in respect of 3 possible effects and considers:

  • Fatigue
  • Corrosion
  • Accidental Damage


In addition MSG-3 recognises the development of structural inspections and age exploration programmes.

Structures programme development and Zonal programmes are integrated into the program and offer the following features:

  • Recognises damage tolerance rules and the supplemental inspection programme.
  • Significant improvement in the structures decision logic
  • The logic is task-oriented, not maintenance process oriented.
  • Improves MRB Maintenance Programme Development
  • Includes servicing / lubrication
  • Improves the description of maintenance tasks
  • Offers a significant improvement in the treatment of hidden functional failures
  • Also considers multiple failures.¬† Sequential failure concepts applied to both Systems / Powerplant and Structures
  • Improved distinction between economic and safety consequences


CS25.1309 Provides for a Standard in relation to equipment systems & installations, by maintain compliance, with CS 25.1309 ensures that the aircraft installations are safe under all perceived operating conditions.

MSG 3 analysis requires that safety effects are addressed ‚Äď the maintenance analysis must adopt this this requirement

The aircraft must be able to perform function under any foreseeable operating conditions and occurrence of failure condition which prevents continued flight and safety landing must be extremely improbable.

Occurrence of other failure conditions which reduce capability of crew to cope with adverse operating conditions must be shown to be improbable.

Warning information should be provided to alert to crew to unsafe system operating conditions.

Systems and controls designed to recognise the potential of Human Error and to minimise crew errors.

Compliance with the above should be shown by analysis and where appropriate tests, utilising either Ground, Flight or Simulator as appropriate.

Testing & Display Considerations include the following:

  • Failure modes – malfunctions and external sources
  • Possibility of multiple failures and undetected failures
  • Any resulting effects concerning either – aeroplane or occupants
  • Crew Warning ‚Äď Ability to take corrective action
  • Capability of detection
  • Power supplies (including consideration 2/3 engine installations)
  • Load shedding
  • Critical environmental conditions


Failure modes effects analysis and Fault trees to be developed in support of the analysis

Note that Fault trees and dependency diagrams are used to provide quantitative assessment of multiple, interactive failures.

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MSG Process, MSG-3