PEAR Model | Human Factors in Aviation Maintenance

human factors

PEAR Model Human Factors

What do you think when I say PEAR? It is not that known fruit, PEAR is a human factors model that helps us understand human factors assonated with human errors in aviation maintenance.

Traditionally, Human Factors researches endeavors have been directed towards flight crew performance and, to a lesser extent, towards the performance of air traffic controllers for a long time.

There was little consideration of the Human Factors issues which could affect aircraft maintenance personnel who inspect and repair aircraft.

While the fact is, human error in aircraft maintenance has indeed had as dramatic an effect upon the safety of flight operation as the errors of pilots and air traffic controllers.

Aviation maintenance technician are confronted with a set of human factors unique within aviation. Oftentimes, they are working in the evening or early morning hours, in confined spaces, in humidity conditions. The maintenance work can be physically strenuous, yet it also required attention to detail.

For more than decades, the PEAR model for human factors has been used as a memory jogger, or mnemonic, to characterize human factors in aviation maintenance.

 Examples of Aviation Maintenance Errors

The fact is that aviation safety relies heavily on aviation maintenance work. When it is not done correctly, it contributes to a significant proportion of aviation accidents and incidents.

 I will mention for you some examples of maintenance errors:

- Installing parts incorrectly.

- Missing parts during maintenance tasks.

- Not performing necessary checks.

Aircraft maintenance errors have been reported as a contributing factor in 15% of major aircraft accidents from 1982 to 1991, at a cost of over 1400 lives.


Safety Management and PEAR Model

As part of the airline’s Safety Management System, policies must be established, hazards must be identified and mitigated.

The human factors program, exemplified by the PEAR model, provides methods for identifying and controlling many of the potential hazards within an organization and should be an integral part of the airline’s SMS program.


Reason’s SWISS CHEESE model, SHELL model, or PEAR model

Human factors specialists may use Reason’s SWISS CHEESE model, SHELL model, or PEAR model.


You may ask | What are the differences between these three human factors models?

Well, the SHELL model is based on ergonomics; the Reason’s SWISS CHEESE model is focused on the importance of organization; the PEAR model is similar to the SHELL model, but is more easily to be understood than the SHELL model, especially in aviation maintenance.

PEAR Model

PEAR model human factors prompt recall of the four important considerations for HF programs:

1- People - who do the work

2- Environment - in which they work

3- Actions - they perform; and

4- Resources - necessary to complete the job.

People - who do the work

 A- Physical Factors

Aviation maintenance technician come in all shapes, sizes, other variables include age, gender, health, experiences, and capabilities. Even though we experience variability from one form to another in physical attributes, for the most part, these characteristics are the most concrete. Our physicality directly impacts the job needing to be done.

 There are 5 Physical Factors, I will try to give you a short explanation for each factor based on my understanding.

1- Physical Size

Physical size deals with issues of anthropometrics, matching the people to the job. At times various tasks may take into consideration the variable of size.

For example, a taller aviation maintenance technician may not need a ladder to perform a task.

 2- Gender

We agree with the principles of gender equality rights. But when it comes to safe lifting weight. The manual handling guidelines suggest that the maximum safe lifting weight for a woman is 16kg, and the maximum safe lifting weight for men is 25kg.

  3- Age

Aging is most likely to affect job performance if job tasks require sensory perception, selective attention, working memory, information processing, rapid reaction, or physical strength.


It’s no secret that people who feel better are more successful in their daily lives. What you may not know is muscle strength can improve your health and job performance.

 5- Sensory Limitations

The effect of losing one or more of our senses can result in an individual’s inability to interact with the work environment.

 B- Physiological Factors

 Physiology is a dynamic state that changes based upon health, habits, and the way we live.

It is a bit more abstract, but this attribute is tied directly to our physical world.

 1- Nutritional factors

Maintaining healthy eating habits reduces anxiety and stress, allows us to think clearly, and keeps us physically fit. As a result, it enhances our confidence.

2- Health

Poor health leads to minimal productivity — when an employee is away from work due to an illness, there will likely be a case of poor productivity.

 3- Lifestyle

A more balanced work lifestyle can lead to higher productivity.


Fatigue can adversely affect safety, health, work performance, and worker productivity, and it can occur if there are risk factors. Fatigue – faced by AMT aviation - is a major human factor that has contributed to many human errors resulting in aircraft incidents and accidents.

 5- Chemical dependency

The body's physical and/or psychological addiction to a psychoactive (mind-altering) substance, such as narcotics, alcohol, or nicotine. You may need to read my previous article about aircraft crashes - central airlines.

 C- Psychological Factors

Psychological differences are not as easy to identify our psychological self takes into consideration our :

  •       experiences,
  •       knowledge,
  •       training,
  •       attitude, and
  •       emotional state

 These factors inform our attitudes, awareness, and cognitive capabilities.


Regularly working long hours and overtime damages professionals' health, making maintenance errors more likely.

2- Experience

Work experience that an aviation maintenance technician holds leads to seriousness in what they do, mature judgment, stability.

3- Knowledge

Knowledge is familiarity or awareness, of someone or something, such as facts (descriptive knowledge), skills (procedural knowledge), or objects (acquaintance knowledge) contributing to an aviation maintenance technician’s understanding.

As we know, knowledge can be acquired in a wide range of ways and from many sources, including but not limited to perception, reason, memory, testimony, scientific inquiry, education, training, and practice.

4- Training

Education, training and hands-on training - Including human factors training - are the most important pieces of an aviation maintenance technician's journey into the career field! Without proper training, aircraft would not be maintained and repaired correctly, leading to safety issues and a halt to the aviation industry.


The working attitude that causes concern is the unwillingness to change, the - that is the way we have always done it- posture prevents the opportunity to evaluate the workplace and institute positive change that can make a work environment safer.

6- Mental or emotional state

The emotional state has been shown to influence perception, thinking, and decision-making.

 D- Psychosocial Factors

The psychosocial self is defined by how we relate to others and this directly impacts teamwork.

1- Interpersonal conflicts

Interpersonal conflicts at work (ICW) refer to negative interactions with others in the workplace, For example, the argument with coworkers and supervisors.

Interpersonal conflicts at work were found to be a risk factor. 



Human factors design should be focused on people in the airlines' existing workforce.  The airlines must match the physical characteristics of each aviation technician to the tasks each one performs.


The airlines must consider factors like each person’s size, strength, age, eyesight and more to ensure each aviation technician is physically capable of performing all the aircraft maintenance tasks making up the job.

A good human factors program considers the limitations of humans and designs the job accordingly.

The Main References:

1- Chapter 14, Human Factors

2- A Model to Explain Human Factors in Aviation Maintenance, B y D r . William B . Johnson , and D r . Michael . Maddox.

Maged Saeed AL-Hadabi

I’m Instructor / Maged Saeed Al-Hadabi. ​ Air Cargo / IATA Dangerous Goods Regulations / Safety Management System Senior Instructor, Auditor [ Yemen Airways] . Approved IATA DGR/ SMS Instructor by Yemen Civil Aviation Authority.

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