MEDA Investigation Process
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A contributing factor is anything that can affect how the maintenance technician or inspector does his or her job, including the technician's own characteristics, the immediate work environment, the type and manner of work supervision, and the nature of the organization for which he or she works.

Data from the U.S. Navy shows that the contributing factors to low-cost/no-injury events were the same contributing factors that caused high-cost/personal-injury events. Therefore, addressing the contributing factors to lower-level events can prevent higher-level events.

In a typical event investigation, as conducted at many airlines in the past, a maintenance event occurs, it is determined that the event was caused by an error, the technician who did the work is found, and the technician is punished. Many times, no further action is taken.

However, if the technician is punished but the contributing factors are not fixed, the probability that the same event will occur in the future is unchanged. The MEDA process finds the contributing factors and identifies improvements to eliminate or minimize these contributing factors in order to reduce the probability that the event will recur in the future.

During a MEDA investigation, it is still necessary to determine whether the event is caused by human behavior and find the individual(s) involved. Instead of being punished, however, the technician is interviewed to get a better understanding of the contributing factors and get the technician's ideas for possible improvements. The information can then be added to a database.

The central part of the MEDA process is making the improvements needed to eliminate the contributing factors. Some of these improvements will be obvious after a single event and others will be apparent only after analyzing a number of similar events. After the improvements have been made, it is important to inform the employees so they know their cooperation has been useful.


It is important to have a discipline policy in place to deal with violation aspects of maintenance events. However, discipline or punishment is only effective for intentional acts. Boeing suggests a policy that:

Boeing supports the "Just Culture" concept, which is based on moving beyond a culture of blame to a system of shared accountability, where both individual and system accountability are managed fairly, reliably, and consistently.


Boeing has updated the MEDA Results Form and User's Guide that reflect the process's new event investigation focus. These materials are provided to anyone at no charge. Boeing will also train operators at no charge if the training takes place in Seattle.


Maintenance events have negative effects on safety and cost. A maintenance event can be caused by an error, a violation, or a combination of errors and violations. Maintenance errors are not committed on purpose and result from a series of contributing factors. Violations, while intentional, are also caused by contributing factors. Most of the contributing factors to both errors and violations are under management control.

Therefore, improvements can be made to these contributing factors so that they do not lead to future maintenance events. The maintenance organization must be viewed as a system in which the technician is one part of the system. Addressing lower-level events helps prevent more serious events from occurring. For more information, please contact William L. Rankin at william.l.rankin@boeing.com.


In addition to MEDA, Boeing has three other investigation processes available to the industry. Like MEDA, these tools operate on the philosophy that when airline personnel (e.g., flight crews, cabin crews, or mechanics) make errors, contributing factors in the work environment are a part of the causal chain. To prevent such errors in the future, those contributing factors are identified and, where possible, eliminated or mitigated. The additional investigation processes are:

  • Ramp Error Decision Aid (REDA), which focuses on incidents that occur during ramp operations.
  • Procedural Event Analysis Tool (PEAT), which was created in the mid-1990s to help the airline industry effectively manage the risks associated with flight crew procedural deviations induced operational incidents.
  • Cabin Procedural Investigation Tool (CPIT), which is designed for investigating cabin crew induced incidents.

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