MEDA Investigation Process
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The central philosophy of the MEDA process is that people do not make errors on purpose. While some errors do result from people engaging in behavior they know is risky, errors are often made in situations where the person is actually attempting to do the right thing. In fact, it is possible for others in the same situation to make the same mistake. For example, if an inspection error (e.g., missed detection of structural cracking) is made because the inspector is performing the inspection at night under inadequate lighting conditions, then others performing a similar inspection under the same lighting conditions could also miss detection of a crack.

MEDA began as strictly a structured error investigation process for finding contributing factors to errors that caused events. However, in the 11 years that MEDA has been in wide use, Boeing has learned that errors and violations both play a part in causing a maintenance-related event.

An error is defined as a human action (i.e., behavior) that unintentionally departs from the expected action (i.e., behavior). A violation is a human action (i.e., behavior) that intentionally departs from the expected action (i.e., behavior).

Today, MEDA is seen as an event investigation process, not an error investigation process. This new approach means that a maintenance-related event can be caused by an error, a violation, or a combination of an error and a violation.


Violations are made by staff not following company policies, processes, and procedures while trying to finish a job not staff trying to increase their comfort or reduce their workload. Company policies, processes, and procedures all can be violated.

The revised version of MEDA acknowledges that violations have a causal effect, and they cannot be ignored if an airline is to conduct a complete investigation. The MEDA process distinguishes between three types of violations: routine, situational, and exceptional.

Routine. These violations are "common practice." They often occur with such regularity that they are automatic. Violating this rule has become a group norm. Routine violations are condoned by management. Examples include:

Situational. The mechanic or inspector strays from accepted practices, "bending" a rule. These violations occur as a result of factors dictated by the employee's immediate work area or environment and are due to such things as:

Exceptional. The mechanic or inspector willfully breaks standing rules while disregarding the consequences. These types of violations occur very rarely.

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