example, if the needle indicates a descent of 200 fpm while  in level flight, use this indication as the zero position.  The ASI presents an indirect indication of the pitch attitude.  In non-turbulent conditions with a constant power setting and  pitch attitude, airspeed remains constant.  [Figure 7-13]  As the  pitch attitude lowers, airspeed increases, and the nose should  be raised.  [Figure 7-14]  As the pitch attitude rises, airspeed  decreases, and the nose should be lowered.  [Figure 7-15]  A  rapid change in airspeed indicates a large pitch change, and  a slow change of airspeed indicates a small pitch change.  Pitch control in level flight is a question of cross-check and  interpretation of the instrument panel for the instrument  information that enables a pilot to visualize and control  pitch attitude. Regardless of individual differences in  cross-check technique, all pilots should use the instruments  that give the best information for controlling the airplane  in any given maneuver. Pilots should also check the other  instruments to aid in maintaining the primary instruments  at the desired indication.  As noted previously, the primary instrument is the one  that gives the most pertinent information for a particular  maneuver. It is usually the one that should be held at a  constant indication. Which instrument is primary for pitch  control in level flight, for example? This question should  be considered in the context of specific airplane, weather  conditions, pilot experience, operational conditions, and  other factors. Attitude changes must be detected and  interpreted instantly for immediate control action in high- performance airplanes. On the other hand, a reasonably  proficient instrument pilot in a slower airplane may rely  more on the altimeter for primary pitch information,  especially if it is determined that too much reliance on the  attitude indicator fails to provide the necessary precise  attitude information. Whether the pilot decides to regard  the altimeter or the attitude indicator as primary depends  on which approach will best help control the attitude. In  this handbook, the altimeter is normally considered as the  primary pitch instrument during level flight.  The bank attitude of an airplane is the angle between the  airplane’s wings and the natural horizon. To maintain a  straight-and-level flightpath, the wings of the airplane are  kept level with the horizon (assuming the airplane is in  coordinated flight). The instruments used for bank control  are the attitude indicator, the heading indicator, and the  turn coordinator.  Figure 7-16  illustrates coordinated flight.  The aircraft is banked left with the attitude indicator and  turn coordinator indicating the bank. The heading indicator  indicates a left turn by apparent clockwise rotation of the  compass card behind the airplane silhouette.  The attitude indicator shows any change in bank attitude  directly and instantly and is, therefore, a direct indicator. On  the standard attitude indicator, the angle of bank is shown  pictorially by the relationship of the miniature aircraft to the  artificial horizon bar and by the alignment of the pointer with  the banking scale at the top of the instrument. On the face of  the standard three-inch instrument, small angles of bank can  be difficult to detect by reference to the miniature aircraft,  especially if leaning to one side or changing a seating position  Attitude Indicator Bank Control Airspeed Indicator (ASI) Figure 7-13. Constant power plus constant pitch equals constant  speed. Figure 7-14.  Constant power plus decreased pitch equals increased  airspeed. Constant Airspeed  Constant Pitch Increased Airspeed Decreased Pitch Decreased Airspeed Increased Pitch Figure 5-13. Constant power plus constant pitch equals constant airspeed.  Figure 5-14. Constant power plus decreased pitch equals increased airspeed..  Figure 7-15. Constant power plus increased pitch equals decreased  airspeed. 7-6