psychological and physiological conditions, such as fatigue,  boredom, illness, anxiety, or preoccupation.  creates a collision hazard or results in a loss of separation  with an aircraft taking off, landing, or intending to land.  The three major areas contributing to runway incursions  are communications, airport knowledge, and flightdeck  procedures for maintaining orientation.  [Figure 1-13] Effective scanning is accomplished with a series of short,  regularly-spaced eye movements that bring successive areas  of the sky into the central visual field. Each movement  should not exceed 10 degrees, and each area should be  observed for at least 1 second to enable detection. Although  horizontal back-and-forth eye movements seem preferred  by most pilots, each pilot should develop a scanning pattern  that is most comfortable to them and adhere to it to assure  optimum scanning. Taxi operations require constant vigilance by the entire flight  crew, not just the pilot taxiing the airplane. During flight  training, the instructor should emphasize the importance  of vigilance during taxi operations. Both the student pilot  and the flight instructor need to be continually aware of the  movement and location of other aircraft and ground vehicles  on the airport movement area. Many flight training activities  are conducted at non-tower controlled airports. The absence  of an operating airport control tower creates a need for  increased vigilance on the part of pilots operating at those  airports.  [Figure 1-14] Peripheral vision can be most useful in spotting collision  threats from other aircraft. Each time a scan is stopped and  the eyes are refocused, the peripheral vision takes on more  importance because it is through this element that movement  is detected. Apparent movement is almost always the first  perception of a collision threat and probably the most important  because it is the discovery of a threat that triggers the events  leading to proper evasive action. It is essential to remember,  however, that if another aircraft appears to have no relative  motion, it is likely to be on a collision course with you. If  the other aircraft shows no lateral or vertical motion, but is  increasing in size, take immediate evasive action.  Planning, clear communications, and enhanced situational  awareness during airport surface operations reduces the  potential for surface incidents. Safe aircraft operations can be  accomplished and incidents eliminated if the pilot is properly  trained early on and throughout their flying career on standard  taxi operating procedures and practices. This requires the  development of the formalized teaching of safe operating  practices during taxi operations. The flight instructor is  the key to this teaching. The flight instructor should instill  in the student an awareness of the potential for runway  incursion, and should emphasize the runway incursion  avoidance procedures. For more detailed information and a  list of additional references, refer to Chapter 14 of the Pilot’s  Handbook of Aeronautical Knowledge. The importance of, and the proper techniques for, visual  scanning should be taught to a student pilot at the very  beginning of flight training. The competent flight instructor  should be familiar with the visual scanning and collision  avoidance information contained in AC 90-48, Pilots’ Role  in Collision Avoidance, and the Aeronautical Information  Manual (AIM). There are many different types of clearing procedures. Most  are centered around the use of clearing turns. The essential  idea of the clearing turn is to be certain that the next maneuver  is not going to proceed into another airplane’s flightpath.  Some pilot training programs have hard and fast rules, such  as requiring two 90° turns in opposite directions before  executing any training maneuver. Other types of clearing  procedures may be developed by individual flight instructors.  Whatever the preferred method, the flight instructor should  teach the beginning student an effective clearing procedure  and insist on its use. The student pilot should execute the  appropriate clearing procedure before all turns and before  executing any training maneuver. Proper clearing procedures,  combined with proper visual scanning techniques, are the  most effective strategy for collision avoidance. 14 CFR part 61 requires that a student pilot receive and  log flight training in stalls and stall recoveries prior to solo  flight.  [Figure 1-15]  During this training, the flight instructor  should emphasize that the direct cause of every stall is an  excessive angle of attack (AOA). The student pilot should  fully understand that there are several flight maneuvers that  may produce an increase in the wing’s AOA, but the stall  does not occur until the AOA becomes excessive. This critical  AOA varies from 16°–20° depending on the airplane design.  [Figure 1-16] The flight instructor must emphasize that low speed is not  necessary to produce a stall. The wing can be brought to an  excessive AOA at any speed. High pitch attitude is not an  absolute indication of proximity to a stall. Some airplanes  are capable of vertical flight with a corresponding low AOA.  Most airplanes are quite capable of stalling at a level or near  level pitch attitude.  A runway incursion is any occurrence at an airport involving  an aircraft, vehicle, person, or object on the ground that  Stall Awareness Runway Incursion Avoidance 1-12