1-13  Figure 1-6.  Fatigue is a threat to aviation safety because it impairs alertness and performance.  Obstacles to Maintaining Situational Awareness  Situational Awareness  Pilots in training should be taught that exercising good judgment begins prior to taking the controls of an aircraft. Often, pilots  thoroughly check their aircraft to determine airworthiness, yet do not evaluate their own fitness for flight. Just as a checklist is used  when preflighting an aircraft, a personal checklist based on such factors as experience, currency, and comfort level can help  determine if a pilot is prepared for a particular flight. The FAA’s “Personal Minimums Checklist” located in Appendix D is an$_{ }$ excellent tool for pilots to use in self-assessment. This checklist reflects the PAVE approach to risk mitigation discussed in the  previous paragraphs.  Worksheets for a more in-depth risk assessment are located in the “FAA/Industry Training Standards Personal and Weather Risk$_{ }$ Assessment Guide” located online at www.faa.gov. This guide is designed to assist pilots in developing personal standardized  procedures for accomplishing PIC responsibilities and in making better preflight and inflight weather decisions.  Flight instructor s  should stress that frequent review of the personal guide keeps the information fresh and increases a pilot’s ability to recognize the  conditions in which a new risk assessment should be made, a key element in the decision-making process.  Situational awareness is the accurate perception and understanding of all the factors and conditions within the four fundamental risk  elements that affect safety before, during, and after the flight. Maintaining situational awareness requires an understanding of the  relative significance of these factors and their future impact on the flight. When situationally aware, the pilot has an overview of the  total operation and is not fixated on one perceived significant factor. Some of the elements inside the aircraft to be considered are the  status of aircraft systems, pilot, and passengers. In addition, an awareness of the environmental conditions of the flight, such as spatial  orientation of the aircraft and its relationship to terrain, traffic, weather, and airspace should be maintained.  To maintain situational awareness, all of the skills involved in ADM are used. For example, an accurate perception of the pilot’s$_{ }$ fitness can be achieved through self-assessment and recognition of hazardous attitudes. A clear assessment of the status of navigation  equipment can be obtained through workload management and establishing a productive relationship with ATC can be accomplished  by effective resource use.  Many obstacles exist that can interfere with a pilot’s ability to maintain situational awareness. For example, fatigue, stress, or work  overload can cause the pilot to fixate on a single perceived important item rather than maintaining an overall awareness of the flight  situation. A contributing factor in many accidents is a distraction, which diverts the pilot’s attention from monitoring the instruments  or scanning outside the aircraft. Many flight deck distractions begin as a minor problem, such as a gauge that is not reading correctly,  but result in accidents as the pilot diverts attention to the perceived problem and neglects to properly control the aircraft.  Fatigue, discussed as an obstacle to learning, is also an obstacle to maintaining situational awareness. It is a threat to aviation safety  because it impairs alertness and performance.  [Figure 1-6]  The term is used to describe a range of experiences from sleepy, or tired,  to exhausted. Two major physiological phenomena create fatigue: sleep loss and circadian rhythm disruption. 