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Maintenance Error Decision Aid (MEDA)

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Category: Human Behaviour Human Behaviour
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The Maintenance Error Decision Aid (MEDA) is a structured process used to investigate events caused by maintenance technician and/or inspector performance.


Developed originally by the Boeing Company in the early 1990s with the active involvement of three major international airlines, a maintenance staff trade union and the FAA, Maintenance Error Decision Aid (MEDA) was the first structured attempt to enhance the value derived from investigation of maintenance error by providing a process in which human error was placed in its full procedural context. It has since been widely adopted - and adapted - as a basis achieving effective maintenance error investigations worldwide.

The MEDA method was developed as a more effective alternative to simply ‘retraining’ employees found to have made maintenance errors. It was realised that by the time a specific individual had been identified as responsible for an error, information about the factors that contributed to the error had often been lost. It was concluded that if the factors which contributed to an error remained, then similar errors would be likely to recur.

Boeing describes the MEDA philosophy as being based on three assumptions:

  • That people want to do the best job possible and do not make errors intentionally
Investigators will get more help from employees who do not feel their competence is in question. The employees are more likely to be helpful in identifying the factors that might have contributed to an error and in suggesting possible solutions.
  • That a series of factors is likely to contribute to an error
Findings on the context of a particular error investigation may have much wider significance for the occurrence of errors generally. Often, matters like difficulty in understanding of documentation (Job Cards, the Aircraft Maintenance Manual, the Illustrated Parts Catalogue or the applicable CMM), inadequate lighting, poor shift handover or aircraft design issues may be disclosed in an investigation. "Fixing" just some of the identified factors will probably be able to significantly reduce the likelihood of most types of error recurring.
  • That most of the factors which contribute to an error can be managed
Involvement of employees close to an error in the investigation of it helps to establish how to manage the issues. Processes can be changed, procedures improved or corrected, facilities enhanced and best practices shared.

The MEDA process is described as having five key stages:

  • Selection of the technical event to be investigated by the maintenance organisation involved
  • Decision on whether the error identified was maintenance-related
  • Investigation using the MEDA results form to record relevant information about the event which disclosed the error and the error that caused the event, the factors contributing to the error and a list of possible prevention strategies.
  • Prevention Strategies review leads to prioritising, implementation and tracking of process improvements
  • Feedback to the workforce advises what changes have been made, explains the value of employee participation and shares the results of the investigation.

Further Reading

Three ‘case studies’ of MEDA application are available through a UK based user group. The incidents are:

  1. Incorrect de-jacking of a large jet aircraft in early 2006
  2. Nose wheel steering impossible - torch found in nose wheel steering cable run
  3. Incorrectly fitted main wheel found after flight