Maintenance Error Decision Aid (MEDA)

April 1, 2001

Maintenance Error Decision Aid (MEDA)

A process to help reduce maintenance errors

By Joe Escobar

April 2001

April 28, 1988 — an Aloha Airlines Boeing 737-200 lost 20 feet off the top of its main cabin during flight, killing a flight attendant and terrifying dozens of passengers. The NTSB report on that incident cited human factors as a contributing cause. It was that accident that began the focus on human factors and how they contribute to maintenance errors.
In the early days of aviation, a large number of accidents were attributed to mechanical failure. In fact, human error only accounted for 20 percent of accidents, whereas mechanical failure was responsible for the other 80 percent.
Today, the scales have tipped in the other direction. Technologies and product engineering have improved so much that mechanical failure now only contributes to 20 percent of accidents. It is human error that has taken the top spot, contributing to 80 percent of accidents.

Education is key
So what can we do to reduce the number of accidents attributed to human factors? It is no small task. Sending a few employees to a "Human Factors" course may make them feel good, and will probably give them plenty of useful information, but it will not solve the problem. Educating yourself on the elements that lead to accidents or incidents may help you spot them and initiate safety nets, but it will not produce a significant reduction in accidents.
In order for a serious effort at accident reduction, there needs to be a complete buy-in by the company — from the top executive to the most junior employee; each and every person must participate in whatever program that is initiated.
Recently, I sat in on a Maintenance Error Investigation course given by Anne Bates, who is a trainer for Midwest Express. In communication with her afterwards, she shared some of the things that has helped her company implement an effective human factors program.
In her presentation, she pointed out that the old views of maintenance error causes need to be changed. In the past, management believed that errors were caused by lack of skill, lack of professionalism, lack of training, or lack of time. In fact, many experts believe that errors are caused by poor design, training, morale, loss of situational awareness, physical health, procedures/policy, and organizational factors. By determining which of these factors led to an incident or accident, the company is able to correct the problem and thus prevent it from recurring.

The MEDA process
Midwest Express uses a process tool developed by Boeing called Maintenance Error Decision Aid (MEDA). Boeing originally developed MEDA to collect more information on maintenance errors. It developed into a project to provide maintenance organizations with a standardized process for analyzing contributing factors to errors and developing possible corrective actions The basic philosophy behind MEDA is:
• Maintenance errors are not made on purpose.
• Most maintenance errors result from a series of contributing factors.
• Many of these contributing factors are part of a company process and, therefore, can be managed.
The MEDA process involves five basic steps: Event, Decision, Investigation, Prevention Strategies, and Feedback.

Event – Examples include an in-flight shutdown or damage to the aircraft. The company needs to determine what events will be investigated.

Decision – After the aircraft is fixed and returned to service, the company determines if the event was maintenance related. If it was, then they perform a MEDA investigation.

Investigation – When using MEDA, one of the key steps is the interview after an event. Effective interviews incorporate the following:
• Introduce yourself and make sure the interviewee is familiar with the MEDA process.
• Use a checklist.
• Follow up on contributing factors alluded to.
• Ask for ideas on needed corrective actions.
• Avoid "Yes" or "No" questions like "Did you use the maintenance manual?" Instead, you can rephrase it as "What kind of written information did you use?"
The investigation process is the one that presents a major challenge to many companies. It involves a culture change in many cases. The company needs to change from a "blame game" philosophy of investigating an accident so that they can determine who needs to get written up. Instead, the actual causal factors need to be uncovered. Was fatigue a factor? Was adequate technical information provided and used? Was the person properly trained to perform the task? These are some of the questions that can help determine root causes.

Prevention strategies – In this step, the company reviews, prioritizes, implements, and tracks prevention strategies (also known as process improvements) in order to avoid or reduce the likelihood of similar errors in the future.

Feedback – The company must provide feedback to the maintenance technicians. A new policy does no good if nobody on the hangar floor knows about it.

Stop the blame game
As discussed earlier, an antiquated discipline policy that seeks blame is not useful in a MEDA type program. If technicians are disciplined for honest errors, they may:
• Hide errors.
• Not talk openly during an investigation.
• Not perform some tasks that are prone to error.
In the long run, a human factors program such as MEDA can significantly affect safety. To learn more about Boeing’s MEDA program, you can view an article titled The Role of Human Factors in Improving Aviation Safety at In addition, Human Factors in Aviation Maintenance and Inspection is available online at

Benefits of MEDA
About 60 operators have implemented some or all of Boeing’s MEDA process. Some of the benefits reported by them are:
• A 16 percent reduction in mechanical delays.
• Revised and improved maintenance procedures and work processes.
• A reduction in airplane damage through improved towing and headset procedures.
• Changes in the disciplinary culture of operations.
• Improvements in line maintenance workload planning.