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At War with the “Dirty Dozen”

Battlefield Tips Against a Mechanic’s Worst Enemy

Reprinted with permission from FAA Aviation News

It’s 1994 on the eve of D-Day, a gravel-voiced Army major barks orders to ready his commando unit for a top-secret suicide mission behind enemy lines. Many might recall this vivid Hollywood scenario when hearing the term “Dirty Dozen.” Although the film is not necessarily the inspiration for Gordon DuPont’s long standing list of elements in the maintenance human error chain, an interesting corollary can be seen in its basic application to the breakdown of safety.

If you’re familiar with the 1967 movie, the major (played by silver-haired, consummate tough guy Lee Marvin) heads a group of rowdy, insubordinate military convicts on a near-impossible assignment. Each soldier brings a distinct weakness to the team, e.g., paranoia or dementia, which, if unchecked, can either individually or collectively endanger the mission and the lives of each team member. Like the movie, the consequences of a mechanic not recognizing and heeding warning signs of errors can prove costly, if not deadly.

The “Lone Frontier”

The study of aviation human factors—or as some would say, the optimization of human performance—dates back to the early 1900s, when Orville and Wilbur Wright first wrestled with how to place a human body in their new flying machine and still have it take to the air. Despite its significance, the human factors buzz often took a backseat to mastering the mechanics of flying and appealing to the budding consumer demand for aviation. Over the years, advancements in technology, along with the multiple layers of security and redundancy, have reduced the risks of flying to where many could consider human factors as the “lone frontier” of aviation safety.

The NTSB reports that approximately 80 percent of all aviation accidents are caused by the failure of humans rather than machine failure. Although pilot operations get the lion’s share of attention when it comes to human factors studies, accident data indicate a need for greater emphasis on the mechanic side of the house. Of course, nothing demonstrated this more dramatically than the 1988 incident when an Aloha B737 suffered an explosive decompression at 24,000 feet. This tragic event, triggered by oversight in maintenance procedures, opened many eyes to the consequences of human error in maintenance and led to a more active FAA role. In the subsequent 20 years, regulatory agencies worldwide developed programs to explore the dynamics of human error and mitigate its effect in aviation maintenance.

Know Thy Enemy

Ask any soldier and you’ll likely be told that the key to a successful battle plan is to know your enemy. Enter the “Dirty Dozen,” the early-1990s brainchild of Special Programs Coordinator Gordon Dupont of Transport Canada. With previous experience as a technical investigator for the Canadian Aviation Safety Board, Dupont witnessed firsthand the tragic results of maintenance and human error. To mitigate these errors, Dupont developed 12 basic factors of error (see Figure 1) ranging from mental, to physiological, to environmental elements, that individually, or in concert, form the core of the error chain that can lead to tragedy.


What exactly is so dirty about the Dirty Dozen?

You see them on break room posters, or in PowerPoint presentations, but is their importance truly recognized? Unfortunately for many maintenance professionals, they can be overlooked and considered common sense guidelines that any good mechanic should recognize. That is the challenge. While appearing obvious and familiar, these elements can be elusive and their danger disguised by the myriad of routine distractions, even when right under your nose. Add the unique hazards of an aviation maintenance environment, e.g., extreme heat or cold, strenuous actions, confined spaces, and the well-known “time is money” mantra, and error has every opportunity to rear its ugly head.

“It’s easy to lose sight of even some of the most basic warning signs of errors,” explains FAA Human Factors National Staff Specialist Jay Hiles. “It’s a domino effect that can quickly get out of control, even for an experienced mechanic.”

Although not specifically listed in the Dirty Dozen, the element most commonly attributed to maintenance-related aircraft accidents is failure to follow procedures. This unfortunate circumstance can be the result of any one or more of the 12 factors, and it underscores the importance of staying on top of your game to recognize all possible warning signs.

Arm Yourself (with Knowledge)

“FAA is leading the way in implementing new programs and training aids in the maintenance human factors field,” said Hiles. “The previous four years have been especially active with several new research and development projects, including a line operations safety audit, as well as a fatigue risk-management study, to help combat this long-time nemesis of mechanics.” In addition, FAA also hosted its first aviation fatigue management symposium in June 2008.

In 2006, FAA, along with a consortium of industry and government human factors experts, released the Operator’s Manual for Human Factors in Aviation Maintenance.

According to FAA Human Factors Chief Scientific and Technical Advisor Dr. Bill Johnson, who contributed to the project, “the manual is recognized among the global aviation community for providing guidance to establish a successful maintenance human factors program.”

The Operator’s Manual is posted on FAA’s newly re-designed Maintenance Human Factors website, Here you’ll find videos, presentations, and a document library containing decades of human factors research all at your fingertips. Check it out!

A discussion of the war against human error wouldn’t be complete without mentioning night vision goggles. Okay, maybe they’re not really night vision goggles. But, you do have at your disposal a set of “human-factors spectacles” that, according to Dr. Johnson, “can open your eyes to threats or things that are about to go wrong.” Putting your spectacles on, says Johnson, means standing back and noticing things that might be less obvious, but are potentially critical in recognizing a dangerous situation. For instance, is the weather affecting my ability to do my job safely? Do I have the proper tools and resources? Did I get enough rest last night? These, and more, are vital considerations on the job. Wearing “human factors spectacles” will provide a better perspective and allow you to take action before something goes wrong.

Your Mission

Are you ready to wage this war? You should be. Like it or not, a mechanic’s daily routine is ripe for the possibility of error every single day. Enemies lurk all around, but luckily there are several weapons to keep them at bay. And, you are not alone. Thanks to the efforts of your “allies” in industry and government worldwide, we continue to see advancements, such as voluntary reporting programs, Safety Management Systems, and strategies to address human error specifically in general aviation maintenance.

“Eliminating risk associated with human factors is an ongoing process,” states Hiles. “Forums such as the annual FAA/Air Transport Association of America, Inc., (ATA) Maintenance Human Factors Symposium, which any aviation maintenance professional can attend, will help the industry keep pace with the continuous evolution of systems, materials, and information technology.”

It’s easy to fall victim to the Dirty Dozen. In most cases they are manifestations of personal work habits that can lead to an innocent or unintentional error. The important point: Recognize the warning signs of error and carefully think through your actions. Being prepared and having a constant and consistent focus on maintenance human factors will send the Dirty Dozen running for cover every time.

Martin Bailey is manager of Flight Standards Service’s Repair Station Branch. Tom Hoffmann contributed to the article. He is associate editor of FAA Aviation News and is a commercial pilot and holds an Airframe and Power plant certificate.


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