The Weakest Link

What is the weakest, most unreliable, least dependable part of any system or process? If you said the human that is operating it or maintaining it, you would be correct. Human Factors is a buzz word in industry these days, but it has been around in the airline world for a long while now. We have special classes on Human Factors - how to recognize them, and how to defend against them. It is something that we take quite seriously, and perhaps you should also.

There are twelve recognized human factors. The “Dirty Dozen” as they are commonly called. They are:

1) Lack of Communication

Communication can be verbal, written or a combination of the two. With a lack of effective communication, maintenance operations will not function safely and efficiently.

2) Complacency

Complacency is the result of constant repetition of maintenance inspections or procedures. It is the false sense of security that occurs after long periods without encountering errors or defects.

3) Lack of Knowledge

Lack of knowledge is not all that uncommon with the changes that are constantly taking place.

4) Distraction

This cause is thought to be responsible for about 15% of all maintenance errors. One leaves a task, (both physically and / or mentally), for any reason and returns thinking that they are further along with the task then they actually are.

5) Lack of Teamwork

This cause is often tied to lack of communication and can be responsible for major errors. With maintenance often involving multitudes of workers, good teamwork becomes essential.

6) Fatigue

Fatigue is very dangerous because, until it becomes extreme, the person is usually unaware that they are fatigued. They are even less aware of what the effects of fatigue are.

7) Lack of Resources

There are times when there may be a lack of resources and a decision must be made between putting the job on hold or figuring out an alternate way to continue.

8) Pressure

Most industries have constant pressure to see tasks completed. The secret to not allowing pressure to become a factor is the ability to recognize when the pressure becomes excessive or unrealistic.

9) Lack of Assertiveness

Maintenance personnel are not normally faced with situations that require them to be assertive. However, there may be a time when something is not right and they will have to be assertive to ensure that a problem is not overlooked.

10) Stress

Stress is a normal part of everyday life until it becomes excessive. The secret to effectively dealing with stress is the ability to recognize when it becomes excessive.

11) Lack of Awareness

This often occurs to very experienced maintenance personnel who fail to fully think about the possible consequences of the work they are doing. This also includes not being constantly aware of your surroundings.

12) Norms

This last factor is a powerful one. Maintenance personnel are inventive types and will develop methods or procedures that may seem to be quicker and more efficient. Deviating from approved procedures may result in problems or failures appearing at a later time. The mere mention of the words “...we’ve always done it that way…” or “...that’s not the way we do it here…” is a clear indicator that a “norm” is in place and thriving.

Each of the “dirty dozen” impacts some part of your operation to some degree or another every single day. Sometimes they are easily recognized and dealt with, but most times they are not. People in general tend to ignore or under estimate their own shortcomings or, worse yet, recognize their shortcomings and continue on anyway.

A Real World Example


The sinking of the USS Guitarro was accidental, and the immediate cause of the sinking was the negligence of certain shipyard employees. This is combined with the contributing factors of inadequate teamwork, lack of communication, lack of awareness, lack of knowledge, and distraction.

The Guitarro Timeline:

4:00 P.M.: A civilian nuclear construction group began an instrument calibration assignment which required the filling of certain tanks, located aft of the ship’s pivot point, with approximately five tons of water.

4:30 P.M.: A civilian non-nuclear construction group began an assignment to bring the ship within a half degree of trim. This entailed the adding of water to tanks forward of the ship’s pivot point to overcome a reported two degree up-bow attitude.


4:30 to 7:45 P.M.: The non-nuclear group continued to add water forward.

7:00 P.M. and again at 7:30 P.M.: A security guard advised the non-nuclear group that the Guitarro was riding so low forward that a one and a half foot wave action, stirred up by boats operating in the river, was causing water to enter an uncovered manhole in the most forward and lowest portion of the ship’s deck. These warnings went unheeded.

7:45 P.M.: The non-nuclear group stopped adding water to the ballast tanks in preparation for their lunch break.


8:00 P.M.: The non-nuclear group left for lunch.

8:30 P.M.: A member of the nuclear group emptying the water from the aft tanks noticed a “...sudden down angle being taken by the boat.” At approximately the same time, the non-nuclear group and others, returning to the ship from lunch, observed the ship was down sharply at the bow with a massive flooding taking place through several large open hatches.


8:55 P.M.: The Guitarro sank.


The tragedy was not caused by lack of formal policies, procedures, or directives. Over 300 pages of instructions, guidelines, and organizational charts meticulously detailed and parceled out responsibilities and authorities.

Despite the elaborate formulation of policies and procedures, something was lost in their translation into practice and the Guitarro went down. Its sinking could have been prevented by the timely exercise of very little common sense and the taking of a few simple precautions.

Reference has been made to two operations which were under way simultaneously on the Guitarro during the late afternoon and early evening of May 15. One operation was being performed aft by a nuclear group and the other was being performed in the forward part of the ship by a non-nuclear group. Neither group knew what the other was doing nor were they apparently aware of each other’s presence. There is a mutual dependency which should require constant communication if operations are to be coordinated and scheduled in the most effective and efficient manner.

The swing shift Foreman to whom this work was assigned testified before a Congressional Subcommittee that he had never before attempted to trim a ship and did not feel qualified to do so, although he had participated to some extent in the trimming operation on the 13th. He stated that although he was told that the Guitarro was bow down he had it checked by one of his workers who reported the bow up two degrees.

It further appears from the testimony before the Subcommittee that only the Nuclear Ship Superintendent and a subordinate knew on the afternoon of May 15 that the non-nuclear side had been requested to recheck the ship’s trim and there is no evidence that they brought this information to the attention of the swing shift nuclear group slated to run the calibration tests or to anyone else on the nuclear side. This suggests that communication within the nuclear section was no better than communication between the nuclear and non-nuclear groups.


The Guitarro was refloated three days later, May 18th. Damages were estimated at between $15.2 million and $21.85 million. The Guitarro was commissioned two and a half years late, on September 9, 1972.

In the mid to late 1970s, The Guitarro was stationed at Point Loma in San Diego, California. She was active in the pre-operational testing of the new Tomahawk cruise missile during this time, launching several of the missiles on a test range off the coast of Southern California.

The Guitarro was decommissioned and stricken from the Naval Vessel Register on May 29, 1992, and entered the Nuclear Powered Ship and Submarine Recycling Program in Bremerton, Washington.

The sinking of the Guitarro is a prime example of the importance of human factors in the work place. Sure, most of us have nothing to do with nuclear powered submarines, but in my airline world I see incidents almost every day that are either directly caused by or exasperated by human factors.

Could a series of events like those that sank the Guitarro happen in your company? The shipyard had policies and procedures in place, their employees were well trained in their area of expertise, and they had an excellent workplace safety record. So, why did the Guitarro sink? Human Factors - the weakest link in any process or procedure.

Shipyard representatives pointed out the fact that the shipyard had been building ships for a long time and no one had been killed and no equipment had been damaged. On May 15, the shipyard’s luck ran out. Proving yet again that Chicken Little only has to be right once.

Article submitted by by Bill Brinkley AP / IA / ASQ
Manager of Reliability and Development
USAirways Express