 Accidents are not inevitable. They can be prevented. Conservation of the Air Force and its combat capability makes it essential to probe the causes of accidents which, in a matter of seconds, can turn the product of thousands of man-hours into scrap metal and destroy the hopes, the skills and the lives of its crews. Scientific investigation and analysis of accidents reveal there are two major causes human error and material failure. And in the final analysis, even the material failures can be traced to human error. Most of these errors are not a result of willful negligence or violation but of a man's failure to act on what he knows. Sometimes we find these errors begin with the initial requirement for a new piece of equipment or in the process of creating the design. Although the design may be correct mechanically, it is difficult to anticipate all the possible human ramifications which may affect it. Sometimes we find these failures in the manufacturing process, installation and testing or in the writing and interpretation of procedures for maintenance and finally in operational use. In the early phases when the equipment is new, the greatest source of error is functional or structural breakdown, material failure. In time, as the bugs are taken out of the system, the major cause of accidents becomes human error. It does little good, however, merely to say that an accident is caused by human error unless we explore what error, under what conditions it occurred, who committed it and why. Human failure occurs in three major areas, communications, human limitations and supervision. Accidents result first when vital communications break down. Second, when the demands of a situation exceed man's limited physical, physiological and psychological capacities. Third, when the integrating function of supervision fails. Man's seldom works alone and this brings into focus one of the major sources of human error, communications. Man's great progress and his fantastic development in cultural and social fields, as well as a material achievement, has depended on his ability to convey his ideas to other men. But any communication is difficult because even a simple object like a tree has many different characteristics. When a man tries to describe it to someone else directly with words and gestures, he frequently fails. The problem is even more difficult when he tries to express abstract thoughts or physical properties such as electricity. The communication of mathematical concepts can be even more difficult. But the problem is further complicated when communication is written or indirect. To help matters along, man has developed symbols which are a compression of words and ideas with previously agreed upon meanings. The problem is still further aggravated in the highly sensitive area of human relations, where the same words mean different things to different people. And the greater the number of stations in any communications chain, the greater the chance for error. Check with the source. There have always been tremendous barriers to man-to-man communication, but today another factor is becoming increasingly important. The communication between man and machine. A large part of it is carried out on a simple direct man-to-machine basis through man's sense of hearing, sight, and touch. But as man ventures into new environments, his communication with machines becomes more complex. He has to derive information from many sources at once. Information about speed, location, altitude, and this information cannot be verified directly by his senses. Today man's life more than ever before depends on this complex man-machine intercommunication. The structure of his communication is vital, and he must be aware of the soft spots where communication is likely to break down. For even simple ideas or orders may be misinterpreted due to insufficient information or too much information that overloads the system and exceeds man's limited ability to absorb it. These are simple things and we are all somewhat aware of them, but unless we clearly understand and accept their implications, they may be the beginning of disaster. Sometimes the failure is due to a lack of sympathy between the sender and the receiver, or a lack of sympathy with the information being received. The receiver unwittingly distorts the meaning of the information because he is emotionally unwilling to accept it. We frequently hear only what we want to hear, as this nursery rhyme demonstrates so well. Old lady, old lady, shall we go sharing? What did you say, sir? I'm a little hard of hearing. Beautiful lady, oh beautiful lady, I said I love you dearly. Thank you kind, sir. I hear you very clearly. Since man needs information before he acts, the lack of clarity sets the stage for mechanical and human failure. Communication breaks down very fast and very often when it isn't clear, when it's garbled. This garbling can occur in many ways, technically by interference or background noise, through poor enunciation or illegible writing. By not being in the proper form of the right channel, all simple things, human errors that cause the loss of valuable men and machines. During the period of recorded history, there is little evidence to indicate that man has changed in any major respect. Among living creatures he is not the strongest or the fastest, but rather a unique compromise. He possesses a central nervous system, but not much different from some reptilian antecedent. He has a circulating system with warm blood, but not much better than that of any other mammal. He has a digestive system that gives him a great foraging range, but even this is equal by that of a rat. If we look at man as if he were a machine, we would say that he is made of three interrelated parts. First, he has a physical structure, flexible, light, strong, and functional. Second, he is a biochemical laboratory, complete with the means for converting food into fuel with filtering systems, heat exchangers, and the ability to replace worn out parts. Third, he is an emotional, psychological computing device of incredible complexity, with systems for controlling movement, acquiring and integrating knowledge, and channeling desire. He has systems that can plan, anticipate, and aspire. Modern man's aspirations carry him into new and hostile environments. Although technically better prepared, he is the same as he has always been. His mechanical, chemical, and psychological abilities are severely limited. When the demands of the situation exceed these limits, man breaks down the result, an accident. When we look at man as a physical structure, we see that he has a remarkably strong, light frame. That he is a mechanical system of levers and balances, flexible, resilient. But in spite of his abilities, he has many built-in limits. He can only reach so far. He can train himself to do involved actions requiring coordination and timing, but he cannot perform maneuvers which are too refined. He can only lift so much. He has a precarious sense of balance. With his eyes closed, he has no sensation of acceleration under the rate of two degrees per second per second. When his sense of balance is contradicted by other sensory systems such as by his vision during flight, simple things confuse him. He becomes disoriented and may get vertigo. For example, as a pilot changes channels on his radio, he changes hands on the stick and unwittingly pushes it aside. When he straightens up, he is level relative to his plane, but confused. In almost any sensory area, some other animal exceeds him. Man is sensitive to sounds in a very limited range of both frequencies and intensities. Man's noble companion and best friend hears much higher frequencies above 20,000 cycles per second. Sound and mechanical vibration will induce fatigue, reduce working efficiency, and produce irritability. If prolonged, noise over 95 decibels can cause men's serious bodily damage and deafness. Many creatures surpass man in tactile sensitivity. His sense of touch is severely limited. If shapes are too nearly alike, he can't tell them apart, even when it's important to him. Modern man protects himself against his environment by designing easily handled mechanical equipment to correct for his limitation, but if it gets cold, his tactile sensitivities are dulled and his hands may become totally useless. As usual, he has a way of coping with the problem, but with gloves, he can hardly rely on touch at all. Man's vision is severely limited. Many birds can see better than he can. Man can only see so far. The size and shape of objects must be easily identifiable to be interpreted. He has problems with color and low levels of illumination. His visual world is full of optical illusions. He brings his own emotional attitudes to what he sees, and this may delude him. Medieval man could readily be transposed to the 20th century. Today, man copes with a highly complex environment with physical abilities no better than he has ever had. For although man's civilization has become more complex, his physical limits have remained constant. He could cope with the high velocities in his new environment were not for overreaching his physical limitations. Because he uses equipment in a way that exceeds his real ability, he makes errors of judgment, not only deadly for himself, but for others. Perhaps the most vital physical limit of man is the fact that he operates in time. A standard time sequence starts with the perception of information through his sensory systems. Then he interprets this information, compiles and integrates it with other information and past learning, and makes a decision. Finally, he responds with action. Man is not always aware of this time cycle. For example, when a light stimulus strikes the eye and from there is transmitted to the brain in the form of a nerve impulse, a measurable lapse of time occurs as much as three-tenths of a second. Recognition takes still more time, perhaps a half-second or more. Then the evaluation, interpretation and the decision all take more time, about a second. After the decision, his response takes several more tenths of a second. There is also a time lag as the machine responds to the control and another for the aircraft to deviate from its flight path. If two aircraft were on a collision course at 600 miles per hour at four seconds before the point of collision, these aircraft would be a mile and a third apart. If excessive time were taken in any one of these steps, if the pilot were to look into the cockpit, look outside, and then refocus his eyes on the instrument panel, this action would take about two seconds, two seconds more than he has. A collision would be inevitable. Physiological man is a ground animal and in the early days of the American farmer, he had little reason to think about himself as a biochemical laboratory. He lived in a relatively simple civilization and most of his needs were met by simple means. He got plenty of sunshine and fresh air. His water was good to drink and he grew most of his own food. He put in a hard day's work but he got plenty of rest. Except for periods of illness when his biochemical laboratory broke down as a result of disease, he lived, at least according to some romantic versions of history, a short but happy life. But man's incredible ingenuity and his insatiable lust for pioneering changed all that. Now there appears to be more automobile exhaust and industrial waste than fresh air. The work is easier and he gets most of it done sitting down. He has plenty of leisure time but gets very little rest. His periods of illness are more frequent but less devastating and his biochemical laboratory seldom breaks down completely but gradually wears away. So that he lives, at least according to the contemporary novel, a long but miserable life. Although his tools are more complex, their operation is simple. Scanning lights, throwing switches and pushing buttons. The work is easier but he lives in a highly dangerous environment. If he wants to stay alive, if he wants to prevent accidents, he must not only take technical precautions but he must understand his own internal physiological limits. Man is highly complicated and it would take an elaborate chemical laboratory to reproduce the biochemical actions taking place in his body. So to put it simply, when the blood is pumped through the body adequately and contains the proper chemicals, his body structures are nourished. His sensory apparatus remains acute. He can arrive at clear-cut decisions and take efficient action. If this biochemical balance is upset, dangerous inefficiency results. Man's most immediate chemical need is for the oxygen in the atmosphere. Without it, life can be sustained only a matter of minutes. He needs oxygen for the production of energy. He takes it into his lungs and from there, it goes into his blood. While the unwanted waste product, carbon dioxide, comes out of the blood and is discharged into the air. The bloodstream carries the oxygen to the hungry tissues. Some toxic gases, however, can prevent man from getting enough oxygen. The most common is carbon monoxide. Taken into the lungs, it prevents the oxygen from being carried by the blood, depriving the tissues of nourishment. Early stages of oxygen deficiency can induce a feeling of well-being and render man incapable of perceiving his impaired abilities. Increased amounts of this toxic gas can lead to asphyxiation, unconsciousness and ultimately death. The modern world requires man to handle toxic materials, both industrially and in daily life, with a deadly over familiarity. Poisoning is common in man's daily life, not only in a highly dramatic way, but also by small insidious doses, deadly because they damage the body tissues and retard or inhibit man's reactions and judgment. These poisons can enter his body through the respiratory tract, or by the way of skin absorption into his bloodstream, or they may enter through his gastrointestinal tract, where they can cause injury to visceral organs such as liver and kidneys. They may affect the blood-forming system in his bone marrow. Man, sometimes unwittingly, sometimes deliberately, uses one of the most common systemic poisons, ethyl alcohol, the primary ingredient of alcoholic beverages. What he hopes will be a stimulant turns out to be a depressant. Ethyl alcohol acts like an anesthetic or narcotic. It can depress the nervous system, eventually causing pain, tremors, acute hallucinations, and general personality deterioration, even psychosis. Proper nourishment is essential. Without it, the tissues may become dehydrated. Waste products build up in the bloodstream with nothing to displace them. Blood flows like a sluggish stream full of mud and debris, barely moving. This reduces man's efficiency and causes errors in his judgment. Similar malfunctions of man's body can occur during illness and even medication may be a contributing factor. And this can be further complicated by self-medication. Perhaps one of the most frequently violated limits of man is his need for rest. Fatigue probably causes and contributes to more accidents than any other single factor. Fatigue may be brought on by either too much or too little physical activity. Efficiency decreases and man tolerates errors much more readily and even fails to see that errors have been committed. After 48 to 72 hours without sleep, the body becomes extremely inefficient. Man grows highly irritable and he is apt to fall asleep involuntarily at any moment. Man used to work and live among rather simple external hazards. But now he ventures into more hostile environments for which he is poorly constructed. Man's body is built to function under the pressure of the atmosphere at sea level. Lack of pressure at high altitude can cause the release of gas bubbles as the liquids in his body evaporate. In effect they boil and this may lead to collapse. Even his breathing 100% oxygen cannot prevent it. Too much pressure creates a crushing effect, such as experience by an astronaut under the force of great acceleration. These G-forces cause incapacitation by slowing down or stopping the flow of blood. Although excessive heat or cold can destroy body cells, man can, with the aid of his technical skill, function over a wider range of temperature than any other animal. But no matter where he exists, he must maintain a constant body temperature of 98.6 degrees. A rise of 5 degrees results in high fever, possible delirium. A rise of only 3 more degrees and death may result. Man travels freely only within very narrow margins of pressure and temperature. He is further limited by his need for fuel, being able to survive about 30 days without food, 3 days without water, and little over 3 minutes without oxygen. It is indeed a small cage within which man lives, confined by pressure, temperature, and fuel limitations. By fantastic technical skill, however, man has succeeded in expanding his living working area into outer space. Modern psychological man is a product of many cultural factors in his heritage, but basically he is a thinking, feeling organism with aptitudes, desires, and emotions. At first he may appear to be all desire, but gradually a system of rewards and punishments begin to satisfy, frustrate, and channel his desire. He responds with varying emotions. When the desire ends in gratification and satisfaction, he responds with pleasure and with love. When frustrated by punishment, he responds with hostility and self-destructive action. As the emotional fabric of his life becomes more complex, both fear of punishment and the desire for satisfaction give rise to anxiety. Just as he develops emotionally in these early years, he also begins to show a variety of aptitudes and abilities. Every man is born with different aptitudes, but no man comes automatically equipped with knowledge. Unlike a machine designed for a specific function, he must learn complicated processes. We can't avoid errors during this period, if we're willing to accept man's psychological limits as applied to learning, we can minimize them. Although some people do some things better than others, everyone has much to learn. Whether it's physical or intellectual activity, a man can only learn so fast and so much. All learning follows approximately the same pattern. The curve of errors plotted against time is generally so constant it's called the learning curve. With practice, each period of time is marked by a decreasing rate of errors. The curve gradually smooths out at some level of efficiency less than perfection. When learning has reached an acceptable level, man must still practice to retain what he's learned. Learning is a slow process because forgetting is a reality. Man forgets at a measurable rate. Of all the new information received during a given lesson, but not yet thoroughly learned, he generally forgets half in the first 24 hours. After that, he gradually forgets more and more until complete forgetting has apparently taken place. After a long lapse, he must learn all over again. However, when something is learned, some undefined change takes place in the nervous system so that although learning was difficult, forgetting is also difficult. For instance, in aircraft design, great care must be taken when changing the location of important switches. For habit may now interfere with new learning. In periods of stress, man will frequently revert to the old way. This matter of unlearning is more of a problem as man gets older. Old learning persists and it takes a stronger stimulus to leave a new impression, but his judgment and reasoning are often better. Although he reacts slower, he solves his problem from a store of experience. He knows that he doesn't see as well as he used to and that after periods of extreme stress, he recuperates slowly. His responsibilities have increased and he remembers the untimely death of many of his contemporaries. All these factors combine to increase his caution. Then his caution wisely tempers his action and allows him to get more satisfaction from his work. But at any age, the most carefully learned and practiced procedures can be upset by emotional variables. If two people have the same basic talents and training, the one with the greatest motivation will consistently perform better. When a man has personal problems, worries or tensions, they can be expected to interfere with his performance. For man is easily distracted. He can become preoccupied with problems unrelated to his job. Or his attention can be overchanalized so that one task alone may monopolize all his energy. Man needs psychological food as well as any other kind of nourishment to cope with the day's problems. For instance, he needs love, so he frequently suffers from get-home-itis, shortcutting his work to hurry home. Sometimes with disastrous results to his associates and to himself. Casual observation does not reveal man's conflicting emotions or the causes. But man has emotional limits and these affect his attitude toward his work. With loss of love, he becomes depressed or hostile. With too much love, with over-protection, he becomes too dependent and lacks confidence. He needs some recognition, reward, status. Otherwise he becomes frustrated, indifferent or an exhibitionist. But with too much recognition, he can become self-centered and egotistical. He needs restraint. With too little, he may become self-indulgent, careless. With too much restraint, he may become frustrated and uncooperative. He needs challenge or he may get bored. But if the challenges are too great, he may lose confidence and give up. He needs stimulation. With too little, he loses interest. And with too much, he gets confused, saturated. And after periods of stimulation, he needs psychological rest and relaxation. The normal well-balanced man is a composite of these emotions in varying degrees. But isolate him from all interests and stimuli, as occur in some situations today, and even the well-balanced man will create fantasies. He needs knowledge. Without it, he may develop anxiety and fear of the unknown. But with too much knowledge, he may get over-involved and lose perspective, put too much importance on details. It's most important that he have an accurate picture of himself, a self-concept that's real. When this picture of himself is distorted, when he thinks of himself as more or less than he is, he is in psychological trouble. Sometimes this image of himself is so far from reality that we must say the man is mentally ill. These more extreme cases may result in either excesses of complete withdrawal, or in attempts to bolster his image by overconfidence, or by fits of great hostility and rage, or even by self-destructive acts and suicide. Fortunately, these abnormal deficiencies are rare. Most emotional disturbances lead only to inefficiency. But when psychological limits are violated over a long period of time, they can contribute as inevitably as any other violation, physical or psychological, to catastrophe. Human errors occur in three broad areas. In communications, when man's interpersonal relations with his environment, with other men and machines, break down. Accidents also occur when the demands of a situation exceed man's physical, physiological and psychological limits. Or when the integrating function, which is supervision, fails. The key to the entire process of decreasing the demands upon the human capability is not only a clear awareness and understanding of the mission, but also controlled supervision at all levels of selection, training and use. The supervisor has a unique role to play in safety and a unique responsibility. There is a good reason why 95% of the recommendations in accidents are directed toward the supervising. In the final analysis, no matter how good the equipment or how reliable, no matter how well selected and trained the men, no matter how well aware they may be of their own limitations, no matter how clear-cut the objective of the mission, and no matter how well this objective may be communicated, unless they are all welded together, accidents happen. Supervision is this welding together of man, machine and mission, this integrating effort that gives strength to the whole structure. It is the tool man can best employ to combat human error. And you are a supervisor, whether you are an executive officer with authority ranging over a great and complex organization, or a technician cracking the whip on the line during an operation, or even when you work alone, for perhaps the most vital facet of supervision is self-supervision. The same basic principles apply at every step of an operation and at every level of command. A supervisor must first know the mission, the plan and its goals, the importance of success, and the results of failure. In every instance, he should know as much about the plan as is required, his place in it, and the place of every machine and of every man working for him. Then he must be sure that the details of the plan can be communicated properly, that the channels up and down the chain of command are functioning well. He must have some system for monitoring the mission, for getting feedback, and for following through himself to be sure the job is getting done safely and well. Once he has the program or mission firmly in mind, he must be able to assign the right task to the right man. To do this, he must know his own strengths and weaknesses. The strengths and weaknesses of his machines, and perhaps most important of all, he must know his man, what they can do and what they can't. He must be sure when he makes the assignments that each man has the authority, commensurate with his responsibility, and accepts these limits, so there will be no passing of the buck. A man can delegate authority, but he can never abdicate his responsibility. A supervisor must back up his man with effective supporting procedures for the maintenance and operation of the machines with technical orders, checklists, and in special areas with special systems like nuclear weapons, with access control, and with challenge and response checks. Here it must be absolutely clear that there is no margin for error. In every system, he must always remember that he is dealing with men as well as machines, and men have basic needs for attention, to be a part of the program, to be able to make suggestions, and have them evaluated and accepted when they are valid. He must be able to see the job from their point of view, what problems they may have. Finally, he must be certain that he provides the security of a safe working environment. When all this is accomplished and the plan is in operation, he still must be prepared for change. The original plan should be all-inclusive but flexible, changing times constantly required new or modified equipment, new skills, and possibly different people. And he must ensure that as changes are introduced, his people are prepared for them with new information. He sees to it that every echelon is aware of and enforces these new procedures. But he must not expect a change to be accepted simply because it is for the better. He must recognize that any change is associated with emotional impact for the individuals involved in it. He must help resolve these emotional disturbances by providing a sympathetic ear and where possible, an opportunity for more training. But he must never allow emotional problems involved in a change to compromise the mission. Finally, he must never allow his own supervision to become an end in itself. It must always be the means to accomplish the mission. His men have the knowledge to get the job done. He has the task of getting them to use that knowledge to function at their best. If he succeeds, safely through good supervision, will be integrated into every stage of the mission. If he fails, catastrophe. The mission is successful only when the integrating function of supervision welds together all facets of the man-machine environment. And whenever the demands of the situation are kept from exceeding man's physical, physiological, and psychological limits, accidents are not inevitable. They can be prevented.