Chapter 14Human FactorsIntroductionWhy are human conditions, such as fatigue, complacency,and stress, so important in aviation maintenance? Theseconditions, along with many others, are called humanfactors. Human factors directly cause or contribute to manyaviation accidents. It is universally agreed that 80 percentof maintenance errors involve human factors. If they are notdetected, they can cause events, worker injuries, wasted time,and even accidents. [Figure 14-1]14-1

Human EnvironmentalConditionsFigure 14-1. Human factors and how they affect people are veryimportant to aviation maintenance.Aviation safety relies heavily on maintenance. When it isnot done correctly, it contributes to a significant proportionof aviation accidents and incidents. Some examples ofmaintenance errors are parts installed incorrectly, missingparts, and necessary checks not being performed. Incomparison to many other threats to aviation safety, themistakes of an aviation maintenance technician (AMT) can bemore difficult to detect. Often times, these mistakes are presentbut not visible and have the potential to remain latent, affectingthe safe operation of aircraft for longer periods of time.AMTs are confronted with a set of human factors uniquewithin aviation. Often times, they are working in the eveningor early morning hours, in confined spaces, on platforms thatare up high, and in a variety of adverse temperature/humidityconditions. The work can be physically strenuous, yet it alsorequires attention to detail. [Figure 14-2] Because of thenature of the maintenance tasks, AMTs commonly spend moretime preparing for a task than actually carrying it out. Properdocumentation of all maintenance work is a key element, andAMTs typically spend as much time updating maintenancelogs as they do performing the work. [Figure 14-3]Human factors awareness can lead to improved quality, anenvironment that ensures continuing worker and aircraftsafety, and a more involved and responsible work force. Morespecifically, the reduction of even minor errors can providemeasurable benefits including cost reductions, fewer missedFigure 14-2. Aviation maintenance technicians (AMTs) are confronted with many human factors due to their work environments.14-2

Elements of Human FactorsHuman factors are comprised of many disciplines.This section discusses ten of those disciplines: ClinicalPsychology, Experimental Psychology, Anthropometrics,Computer Science, Cognitive Science, Safety Engineering,Medical Science, Organizational Psychology, EducationalPsychology, and Industrial Engineering. [Figure 14-5]Figure 14-3. AMT documenting repair work.deadlines, reduction in work related injuries, reduction ofwarranty claims, and reduction in more significant events thatcan be traced back to maintenance error. Within this chapter,the many aspects of human factors are discussed in relation toaviation maintenance. The most common human factors areintroduced along with ways to mitigate the risk to stop themfrom developing into a problem. Several Federal AviationAdministration (FAA) human factor resources are providedto include the most direct link to aviation maintenance humanfactors which can be found at is Human FactorsThe term human factors has grown increasingly popular as thecommercial aviation industry realize that human error, ratherthan mechanical failure, underlies most aviation accidentsand incidents. Human factors science or technologies aremultidisciplinary fields incorporating contributions frompsychology, engineering, industrial design, statistics,operations research, and anthropometry. It is a term thatcovers the science of understanding the properties of humancapability, the application of this understanding to the design,development, and deployment of systems and services, andthe art of ensuring successful application of human factorprinciples into the maintenance working environment.The list of human factors that can affect aviation maintenanceand work performance is broad. They encompass a wide rangeof challenges that influence people very differently as humansdo not all have the same capabilities, strengths, weaknesses,or limitations. Unfortunately, aviation maintenance tasks thatdo not account for the vast amount of human limitations canresult in technical error and injuries. Figure 14-4 shows someof the human factors that affect AMTs. Some are more seriousthan others but, in most cases, when you combine three orfour of the factors, they create a problem that contributes toan accident or incident.The study and application of human factors is complexbecause there is not just one simple answer to fix orchange how people are affected by certain conditions orsituations. Aviation maintenance human factors researchhas the overall goal to identify and optimize the factors thataffect human performance in maintenance and inspection.The focus initiates on the technician but extends to theentire engineering and technical organization. Research isoptimized by incorporating the many disciplines that affecthuman factors and help to understand how people can workmore efficiently and maintain work performance.By understanding each of the disciplines and applying themto different situations or human behaviors, we can correctlyrecognize potential human factors and address them beforethey develop into a problem or create a chain of problemsthat result in an accident or incident.Clinical PsychologyClinical psychology includes the study and application ofpsychology for the purpose of understanding, preventing, andrelieving psychologically-based distress or dysfunction andto promote subjective well-being and personal development.It focuses on the mental well-being of the individual. Clinicalpsychology can help individuals deal with stress, copingmechanisms for adverse situations, poor self image, andaccepting criticism from coworkers.Experimental PsychologyExperimental psychology includes the study of a variety ofbasic behavioral processes, often in a laboratory environment.These processes may include learning, sensation, perception,human performance, motivation, memory, language,thinking, and communication, as well as the physiologicalprocesses underlying behaviors, such as eating, reading, andproblem solving. In an effort to test the efficiency of workpolicies and procedures, experimental studies help measureperformance, productivity, and deficiencies.AnthropometricsAnthropometry is the study of the dimensions and abilities ofthe human body. This is essential to aviation maintenance dueto the environment and spaces that AMTs have to work with.14-3

PoorinstructionsBoringrepetitive jobsLack ofspare partsUnrealisticdeadlinesSubstanceabuseSmelly fumesPersonal lifeproblemsPoor toolcontrolPoor trainingFatigueLoud noisesPoorlydesigned testingfor skill andknowledgeSlipperyfloorsSnowIncompleteor incorrectdocumentationLack of toolsand equipmentPoorcommunicationFigure 14-4. A list of human factors that affect AMTs.For example, a man who is 6 feet 3 inches and weighs 230pounds may be required to fit into a small crawl space of anaircraft to conduct a repair. Another example is the size andweight of equipment and tools. Men and women are generallyon two different spectrums of height and weight. Althoughboth are equally capable of completing the same task witha high level of proficiency, someone who is smaller may beable to perform more efficiently with tools and equipmentthat is tailored to their size. In other words, one size does notfit all and the term “average person” does not apply whenemploying such a diverse group of people.Computer ScienceThe technical definition for computer science is the study ofthe theoretical foundations of information and computationand of practical techniques for their implementation and14-4application in computer systems. How this relates toaviation maintenance is a lot simpler. As mentioned earlier,AMTs spend as much time documenting repairs as they doperforming them. It is important that they have computerwork stations that are comfortable and reliable. Softwareprograms and computer-based test equipment should be easyto learn and use, and not intended only for those with a vastlevel of computer literacy.Cognitive ScienceCognitive science is the interdisciplinary scientific studyof minds as information processors. It includes researchon how information is processed (in faculties such asperception, language, reasoning, and emotion), represented,and transformed in a nervous system or machine (e.g.,computer). It spans many levels of analysis from low-level

Industrial EngineeringClinical PsychologyExperimental PsychologyAnthropometric nization PsychologyCaution20EndangermentLow RiskEducational PsychologyAreaof Concern30Safety EngineeringCognitive ScienceMedical ScienceComputer ScienceFigure 14-5. Human factor disciplines.learning and decision mechanisms to high-level logic andplanning. AMTs must possess a great ability to problem solvequickly and efficiently. They constantly have to troubleshoota situation and quickly react to it. This can be a viscous cyclecreating an enormous amount of stress. The discipline ofcognitive science helps us understand how to better assistAMTs during situations that create high levels of stress sothat their mental process does not get interrupted and effecttheir ability to work.Medical ScienceSafety EngineeringOrganizational PsychologySafety engineering assures that a life-critical system behavesas needed even when the component fails. Ideally, safetyengineers take an early design of a system, analyze it to findwhat faults can occur, and then propose safety requirementsin design specifications up front and changes to existingsystems to make the system safer. Safety cannot be stressedenough when it comes to aviation maintenance, and everyonedeserves to work in a safe environment. Safety engineeringplays a big role in the design of aviation maintenancefacilities, storage containers for toxic materials, equipmentused for heavy lifting, and floor designs to ensure no one slips,trips, or falls. In industrial work environments, the guidelinesof the Occupational Safety and Health Administration(OSHA) are important.Medicine is the science and art of healing. It encompassesa variety of health care practices evolved to maintain andrestore health by the prevention and treatment of illness.Disposition and physical well-being are very important anddirectly correlated to human factors. Just like people comein many shapes and sizes, they also have very differentreactions to situations due to body physiology, physicalstructures, and biomechanics.Organizational psychologists are concerned with relationsbetween people and work. Their interests includeorganizational structure and organizational change, workers’productivity and job satisfaction, consumer behavior,and the selection, placement, training, and developmentof personnel. Understanding organizational psychologyhelps aviation maintenance supervisors learn about thepoints listed below that, if exercised, can enhance the workenvironment and productivity. Rewards and compensations for workers with goodsafety records. Motivated workers that want to do well and worksafely.14-5

Unified work teams and groups that get along andwork together to get the job done right. Treat all workers equally.Educational PsychologyEducational psychologists study how people learn anddesign the methods and materials used to educate people ofall ages. Everyone learns differently and at a different pace.Supervisors should design blocks of instruction that relateto a wide variety of learning styles.Industrial EngineeringIndustrial engineering is the organized approach to the studyof work. It is important for supervisors to set reasonable workstandards that can be met and exceeded. Unrealistic workstandards create unnecessary stressors that cause mistakes.It is also beneficial to have an efficient facility layout so thatthere is room to work. Clean and uncluttered environmentsenhance work performance. Another aspect of industrialengineering that helps in the understanding of human factorsis the statistical analysis of work performance. Concrete dataof work performance, whether good or bad, can show thecontributing factors that may have been present when thework was done.History of Human FactorsAround 1487, Leonardo DiVinci began research in thearea of anthropometrics. The Vitruvian Man, one of hismost famous drawings, can be described as one of theearliest sources presenting guidelines for anthropometry.[Figure 14-6] Around the same time, he also began tostudy the flight of birds. He grasped that humans are tooheavy and not strong enough to fly using wings simplyattached to the arms. Therefore, he sketched a device inwhich the aviator lies down on a plank and works two large,membranous wings using hand levers, foot pedals, and asystem of pulleys. [Figure 14-7] Today, anthropometry playsa considerable role in the fields of computer design, designfor access and maintainability, simplicity of instructions, andergonomics issues.Figure 14-6. Vitruvian Man, one of Leonardo DiVinci’s famousIn the early 1900s, industrial engineers Frank and LillianGilbreth were trying to reduce human error in medicine.[Figures 14-8 and 14-9] They developed the concept ofusing call backs when communicating in the operating room.For example, the doctor says “scalpel” and the nurse repeats“scalpel” and then hands it to the doctor. That is called thechallenge-response system. Speaking out loud reinforces whattool is needed and provides the doctor with an opportunity tocorrect his/herself if that is not the necessary tool. This sameverbal protocol is used in aviation today. Pilots are requiredto read back instructions or clearances given by air trafficFigure 14-7. Leonardo DiVinci’s rendering of a flying device14-6drawings about anthropometry.for man.control (ATC) to ensure that the pilot receives the correctinstructions and gives ATC an opportunity to correct if theinformation is wrong. Frank and Lillian Gilbreth also areknown for their research on fatigue.Also in the early 1900s, Orville and Wilbur Wright werethe first to fly a powered aircraft and also pioneered manyhuman factors considerations. While others were trying to

Devil Hills, near Kitty Hawk, North Carolina, to developthe first practical human interactive controls for aircraftpitch, roll, and yaw. On December 17, 1903, they made fourcontrolled powered flights over the dunes at Kitty Hawk withtheir Wright Flyer. [Figure 14-10] They later developedpractical in-flight control of engine power, plus an angle ofattack sensor and stick pusher that reduced pilot workload.The brothers’ flight demonstrations in the United States andEurope during 1908-1909, awakened the world to the newage of controlled flight. Orville was the first aviator to use aseat belt and also introduced a rudder boost/trim control thatgave the pilot greater control authority. The Wrights’ flighttraining school in Dayton, Ohio included a flight simulatorof their own design. The Wrights patented their practicalairplane and flight control concepts, many of which are stillin use today.Figure 14-8. Frank Gilbreth – Industrial Engineer.Figure 14-10. The Wright Brothers on December 17, 1903, flyingover the dunes at Kitty Hawk with their Wright Flyer.Prior to World War I, the only test of human to machinecompatibility was that of trial and error. If the humanfunctioned with the machine, he was accepted, if not he wasrejected. There was a significant change in the concern forhumans during the American Civil War. The U.S. PatentOffice was concerned about whether the mass produceduniforms and new weapons could effectively be used by theinfantry men.Figure 14-9. Lillian Gilbreth – Industrial Engineer.develop aircraft with a high degree of aerodynamic stability,the Wrights intentionally designed unstable aircraft withcerebralized control modeled after the flight of birds. Between1901 and 1903, the brothers worked with large gliders at KillEvolution of Maintenance Human FactorsWith the onset of World War I (1914–1918), moresophisticated equipment was being developed and theinability of personnel to use such systems led to an increasedinterest in human capability. Up to this point, the focus ofaviation psychology was on the pilot, but as time progressed,the focus shifted onto the aircraft. Of particular concernwas the design of the controls and displays, the effects ofaltitude, and environmental factors on the pilot. The waralso brought on the need for aeromedical research and theneed for testing and measurement methods. By the end ofWorld War I, two aeronautical labs were established, one atBrooks Air Force Base, Texas, and the other at Wright Fieldoutside of Dayton, Ohio.14-7

Another significant development was in the civilian sector,where the effects of illumination on worker productivity wereexamined. This led to the identification of the HawthorneEffect, which suggested that motivational factors couldsignificantly influence human performance.With the onset of World War II (1939–1945), it wasbecoming increasingly harder to match individuals to preexisting jobs. Now the design of equipment had to take intoaccount human limitations and take advantage of humancapabilities. This change took time as there was a lot ofresearch to be done to determine the human capabilities andlimitations that had to be accomplished. An example of thisis the 1947 study done by Fitts and Jones, who studied themost effective configuration of control knobs to be used inaircraft flight decks. Much of this research transcended intoother equipment with the aim of making the controls anddisplays easier for the operators to use.In the initial 20 years after World War II, most human factorsresearch was done by Alphonse Chapanis, Paul Fitts, andArnold Small. The beginning of the Cold War led to a majorexpansion of Department of Defense supported researchlaboratories, and many of the labs established during the warstarted expanding. Most of the research following the war wasmilitary sponsored and large sums of money were granted touniversities to conduct research. The scope of the researchalso broadened from small equipment to entire workstationsand systems. In the civilian industry, the focus shifted fromresearch to participation through advice to engineers in thedesign of equipment.The Pear ModelThere are many concepts related to the science and practiceof human factors. However, from a practical standpoint, it isPEOPLEmost helpful to have a unified view of the things we shouldbe concerned about when considering aviation maintenancehuman factors. A good way to gain this understanding is byusing a model. For more than a decade, the term “PEAR” hasbeen used as a memory jogger, or mnemonic, to characterizehuman factors in aviation maintenance. PEAR promptsrecall of the four important considerations for human factorsprograms, which are listed below. People who do the job. Environment in which they work. Actions they perform. Resources necessary to complete the job.PeopleAviation maintenance human factors programs focus onthe people who perform the work and address physical,physiological, psychological, and psychosocial factors.[Figure 14-11] It must focus on individuals, their physicalcapabilities, and the factors that affect them. It also shouldconsider their mental state, cognitive capacity, and conditionsthat may affect their interaction with others. In most cases,human factors programs are designed around the peoplein the company’s existing workforce. You cannot applyidentical strength, size, endurance, experience, motivation,and certification standards equally to all employees. Thecompany must match the physical characteristics of eachperson to the tasks each performs.The company must consider factors like each person’s size,strength, age, eyesight, and more to ensure each person isphysically capable of performing all the tasks making up thejob. A good human factors program considers the limitationsof humans and designs the job accordingly. An importantPhysical Physical size Sex Age Strengh Sensory limitationsPsychological Nutritional Factors Health Lifestyle Fatigue Chemical dependencyFigure 14-11. People who do the job.14-8Physiological Workload Experience Knowledge Training Attitude Mental or emotional statePsychosocial Interpersonal conflicts

element when incorporating human factors into job design isplanned rest breaks. People can suffer physical and mentalfatigue under many work conditions. Adequate breaks and restperiods ensure the strain of the task does not overload theircapabilities. Another “People” consideration, which also isrelated to “E” for “Environment,” is ensuring there is properlighting for the task, especially for older workers. Annualvision testing and hearing exams are excellent proactiveinterventions to ensure optimal human physical performance.Attention to the individual does not stop at physical abilities.A good human factors program must address physiologicaland psychological factors that affect performance. Companiesshould do their best to foster good physical and mental health.Offering educational programs on health and fitness is oneway to encourage good health. Many companies have reducedsick leave and increased productivity by making healthymeals, snacks, and drinks available to their employees.Companies also should have programs to address issuesassociated with chemical dependence, including tobaccoand alcohol. Another “People” issue involves teamworkand communication. Safe and efficient companies find waysto foster communication and cooperation among workers,managers, and owners. For example, workers should berewarded for finding ways to improve the system, eliminatewaste, and help ensure continuing safety.EnvironmentThere are at least two environments in aviation maintenance.There is the physical workplace on the ramp, in the hangar,or in the shop. In addition, there is the organizationalenvironment that exists within the company. A humanfactors program must pay attention to both environments.[Figure 14-12]PhysicalThe physical environment is obvious. It includes ranges oftemperature, humidity, lighting, noise control, cleanliness,and workplace design. Companies must acknowledge theseENVIRONMENTconditions and cooperate with the workforce to eitheraccommodate or change the physical environment. It takes acorporate commitment to address the physical environment.This topic overlaps with the “Resources” component ofPEAR when it comes to providing portable heaters, coolers,lighting, clothing, and workplace and task design.OrganizationalThe second, less tangible, environment is the organizationalone. The important factors in an organizational environmentare typically related to cooperation, communication, sharedvalues, mutual respect, and the culture of the company.An excellent organizational environment is promoted withleadership, communication, and shared goals associatedwith safety, profitability, and other key factors. The bestcompanies guide and support their people and foster a cultureof safety. A safe culture is one where there is a shared valueand attitude toward safety. In a safe culture, each personunderstands their individual role is contributing to overallmission safety.ActionsSuccessful human factors programs carefully analyze all theactions people must perform to complete a job efficiently andsafely. Job task analysis (JTA) is the standard human factorsapproach to identify the knowledge, skills, and attitudesnecessary to perform each task in a given job. The JTA helpsidentify what instructions, tools, and other resources arenecessary. Adherence to the JTA helps ensure each workeris properly trained and each workplace has the necessaryequipment and other resources to perform the job. Manyregulatory authorities require the JTA serve as the basis forthe company’s general maintenance manual and trainingplan. Many human factors challenges associated with use ofjob cards and technical documentation fall under “Actions.”A crystal clear understanding and documentation of actionsensures instructions and checklists are correct and useable.[Figure 14-13]Physical Weather Location inside/outside Workspace Shift Lighting Sound level SafetyOrganizational Personnel Supervision Labor-management relations Pressures Crew structure Size of company Profitability Morale Corporate cultureFigure 14-12. Environment in which they work.14-9

ACTIONS Steps to perform a task Sequence of activity Number of people involved Information control requirements Knowledge requirements Skill requirements Altitude requirements Certification requirements Inspection requirementsFigure 14-13. Actions they perform.ResourcesThe final PEAR letter is “R” for “Resources.”[Figure 14-14] Again, it is sometimes difficult to separateresources from the other elements of PEAR. In general, thecharacteristics of the people, environment, and actions dictatethe resources. Many resources are tangible, such as lifts,tools, test equipment, computers, technical manuals, and soforth. Other resources are less tangible. Examples includethe number and qualifications of staff to complete a job, theamount of time allocated, and the level of communicationamong the crew, supervisors, vendors, and others. Resourcesshould be viewed (and defined) from a broad perspective. Aresource is anything a technician (or anyone else) needs to getthe job done. For example, protective clothing is a resource.A mobile phone can be a resource. Rivets can be resources.What is important to the “Resource” element in PEAR isfocusing on identifying the need for additional resources.produces, it becomes extremely troublesome. Training, riskassessments, safety inspections, etc., should not be restrictedto attempt to avoid errors but rather to make them visible andidentify them before they produce damaging and regrettableconsequences. Simply put, human error is not avoidable butit is manageable. [Figure 14-15]ETYHUMAN EHuman ErrorHuman error is defined as a human action with unintendedconsequences. There is nothing inherently wrong ortroublesome with error itself, but when you couple error withaviation maintenance and the negative consequences that itSAFRRORFigure 14-15. Safety awareness will help foresee and mitigate therisk of human error.RESOURCES Procedures/work cards Technical manuals Other people Test equipment Tools Computers/software Paperwork/signoffsFigure 14-14. Resources necessary to complete the job.14-10 Ground Handling equipment Work stands and lifts Fixtures Materials Task lighting Training Quality systems

Types of ErrorsUnintentionalAn unintentional error is an unintentional wandering ordeviation from accuracy. This can include an error inyour action (a slip), opinion, or judgment caused by poorreasoning, carelessness, or insufficient knowledge (amistake). For example, an AMT reads the torque values froma job card and unintentionally transposed the number 26 to 62.He or she did not mean to make that error but unknowinglyand unintentionally did. An example of an unintentionalmistake would be selecting the wrong work card to conducta specific repair or task. Again, not an intentional mistakebut a mistake nonetheless.IntentionalIn aviation maintenance, an intentional error should really beconsidered a violation. If someone knowingly or intentionallychooses to do something wrong, it is a violation, whichmeans that one has deviated from safe practices, procedures,standards, or regulations.Kinds of ErrorsActive and LatentAn active error is the specific individual activity that is anobvious event. A latent error is the company issues that leadup to the event. For example, an AMT climbs up a ladder todo a repair knowing that the ladder is broken. In this example,the active error was falling from the ladder. The latent errorwas the broken ladder that someone should have replaced.The “Dirty Dozen”Due to a large number of maintenance-related aviationaccidents and incidents that occurred in the late 1980s andearly 1990s, Transport Canada identified twelve humanfactors that degrade people’s ability to perform effectivelyand safely, which could lead to maintenance errors. Thesetwelve factors, known as the “dirty dozen,” were eventuallyadopted by the aviation industry as a straight forward meansto discuss human error in maintenance. It is important toknow the dirty dozen, how to recognize their symptoms,and most importantly, know how to avoid or contain errorsproduced by the dirty dozen. Understanding the interactionbetween organizational, work group, and individual factorsthat may lead to errors and accidents, AMTs can learn toprevent or manage them proactively in the future.Lack of CommunicationLack of communication is a key human factor that canresult in suboptimal, incorrect, or faulty maintenance.[Figure 14-16] Communication occurs between the AMTand many people (i.e., management, pilots, parts suppliers,aircraft servicers). Each exchange holds the potentialfor misunderstanding or omission. But communicationbetween AMTs may be the most important of all. Lackof communication between technicians could lead to amaintenance error and result in an aircraft accident. Thisis especially true during procedures where more than onetechnician performs the work on the aircraft. It is criticalthat accurate, complete information be exchanged to ensurethat all work is completed without any step being omitted.Knowledge and speculation about a task must be clarified andnot confused. Each step of the maintenance procedure mustbe performed according to approved instructions as thoughonly a single technician did the work.A common scenario where communication is c

programs and computer-based test equipment should be easy to learn and use, and not intended only for those with a vast level of computer literacy. Cognitive Science Cognitive science is the interdisciplinary scientific study of minds as information processors. It includes resea