Development & evaluation of the MEDA process

The authors set out to design a tool that could be used to capture the factors that contribute to error in maintenance. They realized that the cause of error was rarely just one reason, but a process made up of a series of circumstances, and when aligned, had the potential to become an incident or an accident. They wanted to design a process that not only highlighted the error itself, but looked at what other factors led to the incident/accident. Highlighting and analyzing the causes would allow the correct actions to be taken with the possibility to reduce or eliminate future incidents/accidents.
The MEDA process was the outcome of this thought process and the article discusses the evaluation results from field testing the MEDA tool.


In the field test survey participants were asked a series of questions regarding the support they received in their maintenance environment.

Environmental Elements Agree % Not Sure % Disagree %
Written materials are available as necessary 77 12 11
Lessons learned from errors are shared 48 19 33
Technical kept informed about problem areas for errors 46 22 32
Written material is presented in understandable formats 43 38 29
Technical receive effective support from organizations 34 29 37
Technical not afraid to admit errors 29 21 50
Technical receive feedback from supervisor about performance 22 24 54
Technical are satisfied with their working environment 29 21 50
Technical are satisfied with their working environment 29 21 50
Punishment is often used to discipline technicians 45 NR NR
Disciplinary actions are fairly applied and justified 22 35 43
Punishment usually results in improved performance 9 28 63

NR=not reported

Next a 'tool survey' was administered, the intention was to find out if participants found the MEDA process easy to use.

MEDA Process Agree % Not sure / Disagree %
Uses familiar words & terms 85 15
Documentation was understandable 83 17
Documentation was complete 76 24
Sufficient instructions on how to use the process 69 31
Use of listing existing barriers to error that failed on Results Form 67 33

Next questions were asked regarding using MEDA for investigations.

MEDA Usage Agree % Not Sure % Disagree %
The results of the analysis were understandable to me 74 25 1
The results of the analysis are applicable 74 24 2
The Results Form helped me identify contributing factors 71 29 0
I found MEDA easy to use 65 28 7
MEDA guided me in identifying technician error 63 23 4
MEDA guided me in identifying corrective actions 57 40 3
I had cooperation from employees while using MEDA 52 44 4

Participants were then asked questions regarding whether MEDA had been accepted as a reporting tool and were they likely to use it?

MEDA Acceptance Agree % Not Sure % Disagree %
MEDA will yield standardized results 75 22 3
MEDA could replace current error investigation method 72 24 4
Job environment will improve because of MEDA 68 27 5
Maintenance error will reduce because of MEDA 58 35 7
MEDA investigations are supported by management 57 41 2
Maintenance error investigations will increase because of MEDA 57 34 9
Will be less punitive action because of MEDA 35 54 11
MEDA will be accepted in my job environment 34 53 13
Because of MEDA, will be new corrective actions 32 61 7

Post maintenance technician interviews the Subject Survey was distributed to the interviewees with the aim to gather information regarding maintenance technician involvement in the MEDA process.

MEDA Involvement Agree % Not Sure % Disagree %
I did not feel intimidated by the use of MEDA 88 5 7
I thought it was useful to discuss existing barriers 75 25 0
The purpose of using MEDA was made clear 65 23 12
MEDA documentation was made available to me 60 7 33
Using MEDA did not create more work for me 57 33 0
MEDA documentation was understandable 53 35 8
MEDA helped in identifying contributing factors 12 50 38
The results of the analysis were understandable 28 59 13
Results of the analysis were made available to me 36 43 21

Airline managers were asked to participate in the Airline Management Survey which addressed the issue of implementing the MEDA reporting system.

Management Observations of MEDA Agree % Not Sure % Disagree %
I fully agree with the MEDA philosophy 92 8 0
I understand how MEDA investigations are done 67 9 24
Airline has done a good job in MEDA implementation 50 34 16
Strong acceptance of MEDA by Management 85 15 0
Strong acceptance of MEDA by technicians 42 42 16
I have seen positive benefits from MEDA 42 58 0
I strongly support the continued use of MEDA 77 23 0
Other airlines should adopt MEDA 75 25 0
It is important for airlines to share MEDA results 69 31 0
My airline will keep MEDA after field test 38 62 0

The final survey administered to MEDA investigators was the Field Test Follow-up Survey and this contained seven of the same questions asked of the Management.

Investigator Observations of MEDA Agree % Not Sure % Disagree %
Airline has done a good job in MEDA implementation 18 53 29
Strong acceptance of MEDA by technicians 17 46 37
Strong acceptance of MEDA by Management 33 39 28
I have seen positive benefits from MEDA 20 40 40
I strongly support the continued use of MEDA 56 25 19
Other airlines should adopt MEDA 45 40 15
My airline will keep MEDA after field test 22 65 13

The researchers then compared answers between management and the MEDA investigators in order to gauge opinions.

MEDA Comparison Management Agree % Investigator Agree %
Airline has done a good job in MEDA implementation 50 18
Strong acceptance of MEDA by technicians 43 17
Strong acceptance of MEDA by Management 85 33
I have seen positive benefits from MEDA 42 20
I strongly support the continued use of MEDA 77 56
Other airlines should adopt MEDA 75 45
My airline will keep MEDA after field test 38 22


Research Approach

Exploratory research using quantitative and qualitative data collection methods.

The authors set out to exam whether the Maintenance Error Decision Aid was effective in highlighting the factors which cause maintenance error and whether after understanding what caused the error change could be made to prevent reoccurrence. The authors conducted a field test of the decision aid using several different methods to collect data, which included:

  • five different surveys
  • two interviews
  • completed MEDA results form


The MEDA process was field tested by employees across eight airlines and one repair station. Sample size varied depending on the survey being administered.

  • Field test survey - 248 airline employees pre MEDA process usage
  • Tool Survey - 237 airline employees post MEDA process usage (participants being the ones to use the process)
  • Subject Survey - post maintenance technician interview they were asked to complete the survey, 17 were returned (it was not mentioned how many were administered)
  • Airline Management Survey - 13 surveys returned from the nine airlines (does not indicate how many were administered or how the nine returned were distributed)
  • Field Follow-up Survey - 49 returned by MEDA investigators (during the last month of the field test). (Does not indicate how many were administered)


Non-experimental with an aspect of longitudinal design (surveying and resurveying the same participants) using quantitative and qualitative methods of data collection.


The results Form is the dependent variable and the error being reported is the independent variable.
In this study there is no control over the dependent variable, therefore confounding variables cannot be managed. However, the MEDA process relies on the facts of the error being reported, and the opinions of the investigator, and cannot eliminate external factors.


A working party, made up of people from aircraft manufacturer, airlines and the national regulatory authority, designed and developed the MEDA process which was to be used to investigate maintenance error. From this working group came a Results Form and a User's Guide.
The Results Form is what is used to report the incident/accident and is designed to gather information not only from the incident itself, but what could be classed as contributing factors.

Field evaluation was the main goal of the authors. They were looking to assess how the MEDA process was received by the industry and this was achieved by evaluating the data collected, from several different collection methods, across different airlines.
1. Surveys

  • Field Test Survey

a pre survey administered to technicians before they became 'investigators' and before using the MEDA investigative process. Collected opinions on maintenance error and airline maintenance programs.

  • Tool Survey

post survey administered to 'investigators' after the used the MEDA investigative process. Collected opinions about using the MEDA Results Form.

  • Subject Survey

administered to the technician who made the error, who was interviewed as part of the investigation process. Collected their opinions regarding the MEDA process.

  • Management Survey

Filled out by Maintenance Managers. Collected opinions on their acceptance of the MEDA process and how highly they rated the importance of contributing factors.

  • Follow-up Survey

Filled out by the investigators who used the MEDA process and re-asked several of the questions form the Field Test Survey, but of course this time after experiencing the MEDA process.

2. Analysis of completed Result Forms
Looked at for completeness, content of information supplied, amount of information supplied and relevance of informations supplied.

3. Meetings
During and post meetings were held to evaluate the MEDA process. The intention was to receive feedback from the selected airlines on the MEDA process from the persons involved in the MEDA process trial.

Data analysis

Following a variety of data analysis, research results were reported in the form of pictorial tabulated results.

  • Qualitative analysis was conducted through Result Form review and participant interviews (although the interviews were more to do with the MEDA process and then assessed with surveys post interview).
  • Quantitative analysis through the use of surveys and tabulating the response percentage.
  • Follow-up Survey checked for statistical significance in its comparison between Manager and technician opinions.

Generalization potential

The developers of the MEDA process carried out field analysis across several different airlines in different countries. Generally the authors showed that the MEDA process could be used by any airline and the results obtained could be trusted.
There was a significant difference in opinions between managers and technicians in the follow-up survey, showing that technicians were reasonably negative in comparison to managers. However the sample size was relatively small and the authors did not provide information on who returned the surveys for analysis.

1. Rankin, W., Hibit, R., Allen, J., Sargent, R. (2000). Development and evaluation of the Maintenance Error Decision Aid (MEDA) process. International Journal of Industrial Ergonomics, 26 (2000) 261-276.
+++ Notes +++
2. ###

Want to know more?

Boeing - Maintenance Error Decision Aid (MEDA) Users Guide (
Explains what error is, what MEDA is, why it should be used, how to use it effectively and how to carry out an investigation.
MEDA - Investigation Process (
A guide to what MEDA is, the philosophy behind it and how to utilize the tool to get the most out of it.

Contributors to this page

K. Twyman


Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License