performance falls off rapidly. Pilots experiencing this level  of stress are not safe and should not exercise their airman  privileges. Pilots who suspect they are suffering from chronic  stress should consult a physician. Fatigue is frequently associated with pilot error. Some of  the effects of fatigue include degradation of attention and  concentration, impaired coordination, and decreased ability  to communicate. These factors can seriously influence the  ability to make effective decisions. Physical fatigue can result  from sleep loss, exercise, or physical work. Factors such as  stress and prolonged performance of cognitive work can  result in mental fatigue.  Like stress, fatigue also falls into two broad categories: acute  and chronic. Acute fatigue is short term and is a normal  occurrence in everyday living. It is the kind of tiredness  people feel after a period of strenuous effort, excitement, or  lack of sleep. Rest after exertion and 8 hours of sound sleep  ordinarily cures this condition. This type of fatigue has two main effects on performance: Acute fatigue has many causes, but the following are among  the most important to the pilot: A special type of acute fatigue is skill fatigue. This fatigue  can be readily seen in the balloon pilot who, for example,  has driven most or all of the night in order to attend an  event, or perhaps was up for most of the previous night.  [Figure 9-3] Sustained psychological stress accelerates the glandular  secretions that prepare the body for quick reactions during  an emergency. These secretions make the circulatory and  respiratory systems work harder, and the liver releases energy  to provide the extra fuel needed for brain and muscle work.  When this reserve energy supply is depleted, the body lapses  into generalized and severe fatigue. Acute fatigue can be prevented by proper diet and adequate  rest and sleep. A well-balanced diet prevents the body from  consuming its own tissues as an energy source. Adequate  rest maintains the body’s store of vital energy. Chronic fatigue, extending over a long period of time, usually  has psychological roots, although an underlying disease is  sometimes responsible. Continuous high stress levels, for  example, can produce chronic fatigue. Chronic fatigue is  not relieved by proper diet and adequate rest and sleep, and  usually requires treatment by a physician. An individual may  experience this condition in the form of weakness, tiredness,  palpitations of the heart, breathlessness, headaches, or  irritability. Sometimes chronic fatigue even creates stomach  or intestinal problems and generalized aches and pains  throughout the body. When the condition becomes serious  enough, it can lead to emotional illness. $_{Figure 9-3.}$  This pilot drove all night to make an event, but still will  not be able to fly. 9-6 • Depletion of physical energy resulting from  psychological stress. • Psychological stress, and • Physical stress, • Mild hypoxia (oxygen deficiency), • Disruption of the perceptual field—concentrating  attention upon movements or objects in the center of  vision and neglecting those in the periphery. This may  be accompanied by loss of accuracy and smoothness  in control movements.  • Timing disruption—appearing to perform a task as  usual, but the timing of each component is slightly off.  This makes the pattern of the operation less smooth,  because the pilot performs each component as though  it were separate, instead of as a part of an integrated  activity. Fatigue