Human Error and The “Dirty Dozen” (Part One)

Human Error

Human error is defined as a human action with unintended consequences. When you couple error with aviation maintenance and the negative consequences that it produces, it becomes extremely troublesome. Training, risk assessments, safety inspections, etc., should not be restricted to an attempt to avoid errors but rather to make them visible and identify them before they produce damaging and regrettable consequences. Simply put, human error is not avoidable but it is manageable. [Figure 14-17]

Types of Errors

Unintentional

An unintentional error is an accidental wandering or deviation from accuracy. This can include an error in your action (a slip), opinion, or judgment caused by poor reasoning, carelessness, or insufficient knowledge (a mistake). For example, an AMT reads the torque values from a job card and unintentionally transposed the number 26 to 62. He or she did not mean to make that error but unknowingly and unintentionally did. An example of an unintentional mistake would be selecting the wrong work card to conduct a specific repair or task. Again, it is not an intentional mistake but a mistake nonetheless.

Intentional

In aviation maintenance, an intentional error should really be considered a violation. If someone knowingly or intentionally chooses to do something wrong, it is a violation, which means that one has purposely deviated from safe practices, procedures, standards, or regulations.

Active and Latent

An active error is the specific individual activity that is an obvious event. A latent error is the company issues that lead up to the event. For example, an AMT climbs up a ladder to do a repair knowing that the ladder is broken. In this example, the active error was falling from the ladder. The latent error was the broken ladder that someone should have replaced.

The “Dirty Dozen”

Due to a large number of maintenance-related aviation accidents and incidents that occurred in the late 1980s and early 1990s, Transport Canada identified twelve human factors that degrade people’s ability to perform effectively and safely, which could lead to maintenance errors. These twelve factors, known as the “dirty dozen,” were eventually adopted by the aviation industry as a straightforward means to discuss human error in maintenance. It is important to know the dirty dozen, how to recognize their symptoms, and most importantly, know how to avoid or contain errors produced by the dirty dozen. Understanding the interaction between organizational, work group, and individual factors that may lead to errors and accidents, AMTs can learn to prevent or manage them proactively in the future.

Lack of Communication

Lack of communication is a key human factor that can result in suboptimal, incorrect, or faulty maintenance. [Figure 14-18]

Communication occurs between the AMT and many people (i.e., management, pilots, parts suppliers, aircraft servicers). Each exchange holds the potential for misunderstanding or omission. But communication between AMTs may be the most important of all. Lack of communication between technicians could lead to a maintenance error and result in an aircraft accident. This is especially true during procedures where more than one technician performs the work on the aircraft. It is critical that accurate, complete information be exchanged to ensure that all work is completed without any step being omitted. Knowledge and speculation about a task must be clarified and not confused. Each step of the maintenance procedure must be performed according to approved instructions as though only a single technician did the work.

A common scenario where communication is critical and a lack thereof can cause problems, is during shift change in an airline or fixed base operator (FBO) operation. A partially completed job is transferred from the technician finishing his or her workday to the technician coming on duty. Many steps in a maintenance procedure are not able to be seen or verified once completed due to the installation of components hiding the work. No steps in the procedure can be omitted and some steps still to be performed may be contingent on the work already completed. The departing technician must thoroughly explain what has occurred so that the arriving technician can correctly complete the job. A recounting of critical steps and any difficulties encountered gives insight. A lack of communication at this juncture could result in the work being continued without certain required operations having been performed.

The approved steps of a maintenance procedure must be signed off by the technician doing the work as it is performed. Continuing a job that has been started by someone else should only occur after a face-to-face meeting of technicians. The applicable paperwork should be reviewed, the completed work discussed, and attention drawing to the next step. Absence of either a written or oral turnover serves as warning that an error could occur.

It is vital that work not be continued on a project without both oral and written communication between the technician who started the job and the technician continuing it. Work should always be done in accordance with the approved written procedure and all of the performed steps should bear the signature of the technician who accomplishes the work. If necessary, a phone call can be made to obtain an oral turnover when technicians cannot meet face-to-face at the work area. In general, the technician must see his or her role as part of a greater system focused on safe aircraft operation and must communicate well with all those in that system to be effective.

Complacency

Complacency is a human factor in aviation maintenance that typically develops over time. [Figure 14-19]

As a technician gains knowledge and experience, a sense of self satisfaction and false confidence may occur. A repetitive task, especially an inspection item, may be overlooked or skipped because the technician has performed the task a number of times without ever finding a fault. The false assumption might be made that inspection of the item is not important. However, even if rare, a fault may exist. The consequences of the fault not being detected and corrected could cause an incident or accident. Routine tasks performed over and over allow time for the technician’s mind to wander, which may also result in a required task not being performed.

When a technician finds him- or herself performing work without documentation, or documenting work that was not performed, it is a sign that complacency may exist. Approved, written maintenance procedures should be followed during all maintenance inspections and repairs. Executing the proper paperwork draws attention to a work item and reinforces its significance.

To combat complacency, a technician must be trained to expect to find the fault that created the inspection item in the first place. He or she must stay mentally engaged in the task being performed. All inspection items must be treated with equal importance, and it must never be assumed that an item is acceptable when it has not been inspected. A technician should never sign for any work that has not been performed. Prior to the pen touching the paper for a signature, the technician should read the item before signing and confirm it has been performed.

Lack of Knowledge

A lack of knowledge when performing aircraft maintenance can result in a faulty repair that can have catastrophic results. [Figure 14-20]

Differences in technology from aircraft to aircraft and updates to technology and procedures on a single aircraft also make it challenging to obtain the knowledge required to perform airworthy maintenance.

All maintenance must be performed to standards specified in approved instructions. These instructions are based on knowledge gained from the engineering and operation of the aircraft equipment. Technicians must be sure to use the latest applicable data and follow each step of the procedure as outlined. They must also be aware that differences exist in the design and maintenance procedures on different aircraft. It is important for technicians to obtain training on different types of aircraft. When in doubt, a technician with experience on the aircraft should be consulted. If one is not available, or the consulted technician is not familiar with the procedure, a manufacturer’s technical representative should be contacted. It is better to delay a maintenance procedure than to do it incorrectly and cause an accident.

Distraction

A distraction while performing maintenance on an aircraft may disrupt the procedure. [Figure 14-21]

When work resumes, it is possible that the technician skips over a detail that needs attention. It is estimated that 15 percent of maintenance related errors are caused by distractions.

Distractions can be mental or physical in nature. They can occur when the work is located on the aircraft or in the hangar. They can also occur in the psyche of the technician independent of the work environment. Something as simple as a cell phone call or a new aircraft being pushed into the hangar can disrupt the technician’s concentration on a job. Less visible is a difficult family or financial matter or other personal issues that may occupy the technician’s thought process as work is performed. This can make performance of the required maintenance less effective.

Whatever their nature, numerous distractions can occur during the course of maintaining an aircraft. The technician must recognize when attention to the job at hand is being diverted and assure that work continues correctly. A good practice is to go back three steps in the work procedure from when distraction occurred and resume the job from that point. Using of a detailed step-by-step written procedure and signing off each step only after it is completed also helps. Incomplete work can be marked or tagged, especially when the technician is pulled from the work by a distraction, and it is unknown when work will be resumed and by whom. Disconnect any connector and leave it plainly visible if an installation is not complete. There is a tendency to think a job is finished when a component is “hooked up.” Similarly, when a step in the maintenance procedure is complete, be sure to immediately lock wire or torque the fasteners if required. This can be used as an indication that all is well up to that point in the procedure.

Lack of Teamwork

A lack of teamwork may also contribute to errors in aircraft maintenance. [Figure 14-22]

Closely related to the need for communication, teamwork is required in aviation maintenance in many instances. Sharing of knowledge between technicians, coordinating maintenance functions, turning work over from shift to shift, and working with flight personnel to troubleshoot and test aircraft are all are executed better in an atmosphere of teamwork. Often associated with improved safety in the workplace, teamwork involves everyone understanding and agreeing on actions to be taken. A gear swing or other operational check involves all the members of a team working together. Multiple technicians contribute to the effort to ensure a single outcome. They communicate and look out for one another as they do the job. A consensus is formed that the item is airworthy or not airworthy.

The technician primarily deals with the physical aspect of the aircraft and its airworthiness. Others in the organization perform their roles and the entire company functions as a team. Teams can win or lose depending on how well everyone in the organization works together toward a common objective. A lack of teamwork makes all jobs more difficult and, in maintenance, could result in a miscommunication that affects the airworthiness of the aircraft.

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