30.0  29.9  29.8  Bank control  Figure 5-16. Instruments used for bank control.  slightly. The position of the scale pointer is a good check  against the apparent miniature aircraft position. Disregarding  precession error, small deviations from straight coordinated  flight can be readily detected on the scale pointer. The  banking index may be graduated as shown in  Figure 7-17 ,  or it may be graduated in 30° increments. and predictable, but the obvious advantage of the attitude  indicator is an immediate indication of both pitch attitude  and bank attitude in a single glance. Even with the precession  errors associated with many attitude indicators, the quick  attitude presentation requires less visual effort and time for  positive control than other flight instruments.  The bank attitude of an aircraft in coordinated flight is shown  indirectly on the heading indicator, since banking results in  a turn and change in heading. Assuming the same airspeed  in both instances, a rapid movement of the heading indicator  (azimuth card in a directional gyro) indicates a large angle  of bank, whereas slow movement reflects a small angle of  bank. Note the rate of movement of the heading indicator  and compare it to the attitude indicator’s degrees of bank.  The attitude indicator’s precession error makes a precise  check of heading information necessary in order to maintain  straight flight.  When deviations from straight flight are noted on the heading  i ndicator, correct to the desired heading using a bank angle no  greater than the number of degrees to be turned. In any case,  limit bank corrections to a bank angle no greater than that  required for a standard rate turn. Use of larger bank angles  requires a very high level of proficiency, and normally results  in overcontrolling and erratic bank control.  The miniature aircraft of the turn coordinator gives an  indirect indication of the bank attitude of the airplane.  When the miniature aircraft is level, the airplane is in  straight flight. When the miniature airplane is aligned with  one of the alignment marks and the aircraft is rolling to the  left or right the indication represents the roll rate, with the  alignment marks indicating a roll of 3 degrees per second  in the direction of the miniature aircraft. This can be seen  in level flight when a bank is introduced either to the left  or the right. The turn coordinator’s indicator will indicate  the rolling motion although there is no turn being made.  Conversely, a pedal input to the right or left causes the aircraft  to turn momentarily about its vertical axis (with no rolling  motion) with an indication of turn on the turn coordinator.  After the turn becomes stabilized and the aircraft is no  longer rolling, the turn coordinator displays the rate of turn  with the alignment marks equaling a turn of 3 degrees per  second. The turn coordinator is able to display both roll and  turn parameters because its electrically-powered gyroscope  is canted at an angle. As a result, the turn-and-slip indicator  provides both roll and turn indications. Autopilots in general  aviation today use this instrument in determining both roll  and turn information. After the completion of a turn, return  to straight flight is accomplished by coordinated aileron and  The instrument depicted in  Figure 7-17  has a scale pointer  that moves in the same direction of bank shown by the  miniature aircraft. In this case, the aircraft is in a left 15°  bank. Precession errors in this instrument are common  0°  30°  45°  60°  90°  Figure 7-17.  Bank interpretation with the attitude indicator. Figure 7-16.  Instruments used for bank control. Heading Indicator Turn Coordinator 7-7