Human factors and aircraft maintenance

Human factors and aircraft maintenance

Anthony Wurmstein

Human factors and aircraft maintenance, what’s a maintainer to do? If you look at past mishaps, we spend a lot of time looking at aircrew human factors, but what about the person turning the wrench and making the aircraft fly? They are a human factor, and the Air Force needs to look at how we can prevent the maintenance human factor mishap. We hope to provide you with some information that you, the supervisor and the individual, can use to help understand human factors in aircraft maintenance.


What is Human Factors?

Human factors is the science of analyzing the limitations of humans as we interact with the environment and preventing or mitigating the inevitable human error. The limitations of humans come in five flavors and are known as the Five Ps: Physical (heat, cold, etc.); Physiological (oxygen, blood flow, etc.); Psychological (senses, information processing, etc.); Psychosocial (team interaction, communication, etc.) and Pathological (illness, injury). Each of these areas is a profession by itself, but together they make up the field of human factors. Human factors lets us look at not just individual human failures but the failures in the systems that we humans create. “OK,” you say. “That’s all great, but how does it help me?” Well, in order to analyze these failures and develop strategies to prevent them, you need a structure or “taxonomy” to organize the different types of failure.


What Is the Human Factors Taxonomy?

This is how we apply human factors to a mishap to determine the cause of the human failure or error that contributed or led to the mishap. If you look at the human factors taxonomy charts (Charts 1-4), you can see we start at the organizational influences and work our way down to the individual acts. This ensures we look at all aspects of the mishap to find the root cause–not the easy answer.

We start by looking at organizational influences or culture (Chart 1). These are the factors in a mishap where the decisions of upper-level management directly affect supervisory practices, conditions and actions of the operator, and result in system failure, human error or unsafe situation. This could be resource management or acquisition, organizational climate or organizational process.

These factors apply when upper-level management sets up or fails to provide an adequate safety environment, structure, policies, procedures or equipment that influences individual actions and results in human error or an unsafe condition. The processes fail when operations, procedures, ORM and oversight negatively influence individual, supervisory, and/or organizational performance and results in unrecognized hazards and/or an uncontrolled risk. Have you ever heard of a mishap where the cause was a procedure that was overlooked as being wrong until the mishap? It happens every year and even cost one maintainer his life.


The next level is supervision, which is a factor in a mishap if the methods, decisions or policies of the supervisory chain of command directly affect practices, conditions, or actions of individuals and results is human error or an unsafe condition (Chart 2). The main aspects of the supervision factors are inadequate supervision, planned inappropriate operations, failure to correct a known problem and supervisory violations.


How do we define inadequate supervision? In a mishap sequence, it would be when supervision proves to be inappropriate or improper, and fails to identify a hazard, recognize or control a risk, provide guidance, training and/or oversight that result in human error or an unsafe situation. How about when supervision is supposed to perform an In-Process Inspection and doesn’t?

The next supervisory item is planned inappropriate operations. This is a factor in the mishap sequence when supervision fails to adequately assess the hazards associated with an operation and allows for unnecessary risk. Additionally, supervision may allow non-proficient or inexperienced personnel to attempt missions/tasks beyond their capability or when crew or flight makeup is inappropriate for the task or mission assigned. We had one mishap during an engine run where supervision planned an engine run operation that ended up with the aircraft jumping chocks.

Another factor is failure to correct a known problem. This is when supervision fails to correct known deficiencies in documents, processes or procedures, or fails to correct inappropriate or unsafe actions of individuals and this lack of supervisory action creates an unsafe situation. How often do we hear, “This is the way we have always done it?” Too often! Supervisors knew the people were violating the rules, or supervision said to violate the rule, and nothing was done to prevent the mishap. How many cases are out there today where supervisors watch a young inexperienced troop do things wrong and don’t correct them on the spot? This sets the person up for failure in the future.

The final supervisory factor is supervisory violations. This is the most serious factor after failing to correct the problem. Here is where supervision, while managing organizational assets, willfully disregards instructions, guidance, rules or operating instructions, and this lack of supervisory responsibility creates an unsafe situation. Any supervisor guilty of this act needs to be shot. When we visit units, we always ask the question, “Are you told to violate tech data?” The answer we get is no, but … “You have 20 minutes to get the job done by the book.” Is this a supervisory violation?

The next group of factors is the preconditions (Chart 3). These mishap factors are the active and/or latent preconditions that include three main areas: the environmental factors, the condition of individuals, and the personnel factors that result in human error or an unsafe condition.

Environmental factors are the physical or technological factors that affect practices, conditions and actions of individuals. Some examples of the physical restrictions are reduced vision due to weather, workplace, or noise. Technological conditions are when aircraft, vehicle or workplace design affects the actions of individuals. This could be anything from switch positions to small confined spaces.


The condition of individuals is the physical/mental limitations, cognitive, adverse physiological states, and psycho-behavioral factors. The physical/mental limitations are when the person lacks the capabilities either physically or mentally to cope with the situation. This could be their learning ability, technical knowledge, or memory issues.

The cognitive factors are attention management conditions such as inattention, channelized attention, cognitive task saturation, confusion, distraction and habit pattern interference, a key factor for maintenance. We are creatures of habit, and many mishaps are caused when habit lets us forget to do something, like install a cotter pin or properly torque a nut.

The adverse physiological states are when the person is on prescribed drugs, or when an injury, illness or a pre-existing injury, illness or deficit affects your ability to perform the task at hand. Fatigue is found here, as well as sleep deprivation and physical task over-saturation. Physical task over-saturation is one we maintainers need to look at. It occurs when the number of manual tasks to perform in a compressed timeframe exceeds the individual capacity to perform them. How many of us can relate to compressed schedules and too much work?

The last part of these factors is the psychobehavioral factors. This covers such things as a pre-existing personality or psychological disorder, emotional state, personality style, overconfidence in capabilities, pressing beyond known capabilities, complacency, inadequate, misplaced, or excessive motivation, overaggressive behavior, and-one many maintainers may look at-burnout or motivational exhaustion. All these together look at the condition/state of the people performing the task at the time of a mishap to determine if there were other factors that could have led them down the mishap path.

The final set of preconditions is the personnel factors or self-imposed stress or crew resource management (CRM). Many people think CRM is just for aircrew, but they are wrong. CRM applies to maintenance, because we have tow crews, refuel crews, launch and recovery crews, hot-pit crews … and how many other crews can you name? CRM deals with communications between team members, preparation for the mission, crew leadership, analysis of the situation and crew coordination. Any slip of these factors and we can damage an aircraft or cause an injury in seconds. Just look at the number of towing mishaps we have had in the last few months, and you can see where CRM needs to be applied.

We are responsible to take care of ourselves, and self-imposed stress is the last of the personnel factors. This deals with our physical fitness for the mission, our nutrition, crew rest (Yes, maintenance needs rest as well; see AFI 21-101), self-medication and unreported disqualifying medical condition. Aircrew can’t fly on medications or when sick, so why should the person who makes the aircraft fly be able to work? This isn’t an excuse to get out of work, but you need to look at your capability to safely and correctly perform the mission.

The last set of human factors is acts (Chart 4). These are the factors most closely tied to the mishap and can be described as active failures or actions by the operator that result in human error or an unsafe condition. These can be an error or a violation. A violation is the most serious, as it is the willful disregard for rules and instructions and lead to an unsafe condition. Violations are deliberate acts. Examples are failure to follow tech data or an accepted procedure/practice, and lack of discipline. This is the disregard for normal and necessary procedures and restrictions in published instructions, regulations, rules of engagement or other official direction. Remember: If the rules are wrong, there are methods to correct them.

Errors are when the mental or physical activities of the operator fail to achieve their intended outcome as a result of skill-based, perceptual, or judgment and decision-making errors leading to an unsafe act which is unintended. This is what many people would call an “honest mistake.”

Skill-based errors are inadvertent operation of a machine, checklist or procedural error, and over- or under-control of a system. This could be such things as hitting the wrong button, missing a step in the checklist or responding inappropriately to system operation.

The next group of errors is judgment or decision-making errors. This could be risk assessment, task mis-prioritization, rushed or delayed necessary action, ignored caution or warning and improperly executed procedure. Every day on flightlines around the world, our maintainers are faced with many decisions that rely on their judgment and expertise to be exact. How well we train them to deal with these choices determines if we create an unsafe situation or not.

The final error is the perceptual error or the misperception of an object, threat or situation that results in human error. This can apply to towing mishaps where the tow supervisor or driver misjudged the distance between the aircraft and another object. We have listed a bunch of different factors that most of you should be able to see on your flightline, and hopefully you can use them to prevent a mishap.

How is Human Factors applied to a mishap?

Now that you have the basic description of the different human factors that can apply to maintainers, how are these applied? We took a look at the Class A and Class B maintenance mishap causal findings in FY03 to see what we could determine. The three of us, a human factors physiologist, a maintenance officer and a maintenance chief, spent four hours going over the mishaps, and many times our judgment of what was the true cause was different. Not being part of the investigation, we had to rely on the mishap narrative to make our conclusions. Some mishaps have more than one cause, so don’t try to add up the numbers.

The first category of causes we found was supervision, which wasn’t a major factor in the majority of mishaps but was a cause in eight of them. The most frequent was inadequate supervision, oversight or leadership. Here, we have mishaps where supervision failed to detect bad safety wire, or a person was directed to perform a task they weren’t proficient at, with no supervision. We have a young maintenance force that needs the help of the old hats to ensure they have proper training, adequate supervision and follow-up to key tasks.

We found that organizational influences were causes in 12 mishaps, with organizational processes being the cause of 10 of the 12. How many times do we find out after a mishap that there is a process that has been going on for years that everyone “accepts” as the right way? An example of accepted practice is the MH-53 helicopter rotor blade weights. After a Class A mishap, it was found that the wrong hardware had been installed. An inspection of the fleet showed that only one aircraft had the correct hardware. Everyone had been installing the wrong length bolts, nuts, and washers, even though the tech data was correct. The biggest factor is that the safety hazard was unrecognized. A method to help prevent this unrecognized hazard is to have someone from outside your organization take a look at your practices. A good place to start is your wing safety office and their annual inspection. You can request a staff assistance visit from headquarters and view it as helping you prevent a mishap. It is easier to be proactive than to react to a major mishap. Then you get help you really don’t want.

To no one’s surprise, unsafe acts were the main cause of the maintenance mishaps, with violations being the No. 1 cause. Of the mishaps we looked at, we found skill-based errors to be the cause in three mishaps, and judgment and decision-making errors the cause in 10 mishaps. As we had suspected, intentional failure to use accepted procedure was the No. 1 cause of mishaps. When people willfully disregard tech data, we are setting ourselves up for failure, and a lot more work during a very busy time in our Air Force. Some examples of failing to follow tech data are an engine technician failing to properly safety wire bolts and the engine failing on the test cell, and a tow supervisor deciding to tow an aircraft into the hangar without wing walkers. These are bad choices that you can’t write off as an honest mistake.

How can I use Human Factors to prevent mishaps at my unit?

The best thing you can do is work with your people, wing safety and the medical folks to ensure you stay alert for changes and problem areas at your location. By being aware of the human factors that influence our workforce and which affect their decisions and ability to perform the mission, you can prevent a mishap and/or recognize when unsafe conditions are created. In addition, you can use this to educate your supervisors, upper- and mid-level, to look beyond the task at hand and take care of your people. There are people at your base who can help if you don’t understand the human factors puzzle. Few people do. Your wing safety office has received training on human factors, plus almost every base with a flying operation has a flight surgeon and someone trained in human factors in the medical group. These experts are there to help. All you have to do is ask.

It’s very hard for us to read a mishap narrative and get the information needed to make an accurate assessment of what were the human factors, so we need you to help us. When you perform an investigation of a maintenance mishap, look at the human factors to help determine the root cause. If you need help, your wing safety office and medical group are there to provide assistance. Be safe, and never forget that we are human beings!





COPYRIGHT 2004 U.S. Air Force, Safety Agency

COPYRIGHT 2004 Gale Group