the helicopter is still turning, make a small change of bank attitude to center the turn needle and stop the movement of the heading indicator. the miniature aircraft and the horizon bar of the attitude indicator are substituted for the actual helicopter and the natural horizon. Any change in bank attitude of the helicopter is indicated instantly by the miniature air- craft. For proper interpretations of this instrument, you should imagine being in the miniature aircraft. If the helicopter is properly trimmed and the rotor tilts, a turn begins. The turn can be stopped by leveling the miniature aircraft with the horizon bar. The ball in the turn-and-slip indicator should always be kept centered through proper pedal trim.  The angle of bank is indicated by the pointer on the banking scale at the top of the instrument. [Figure 12- 14] Small bank angles, which may not be seen by observing the miniature aircraft, can easily be deter- mined by referring to the banking scale pointer.  In coordinated flight, the heading indicator gives an indirect indication of the helicopter’s bank attitude. When a helicopter is banked, it turns. When the lateral axis of the helicopter is level, it flies straight. Therefore, in coordinated flight, when the heading indi- cator shows a constant heading, the helicopter is level laterally. A deviation from the desired heading indi- cates a bank in the direction the helicopter is turning. A small angle of bank is indicated by a slow change of heading; a large angle of bank is indicated by a rapid change of heading. If a turn is noticed, apply opposite cyclic until the heading indicator indicates the desired heading, simultaneously checking that the ball is cen- tered. When making the correction to the desired head- ing, you should not use a bank angle greater than that required to achieve a standard rate turn. In addition, if the number of degrees of change is small, limit the bank angle to the number of degrees to be turned. Bank angles greater than these require more skill and preci- sion in attaining the desired results. During straight- and-level flight, the heading indicator is the primary reference for bank control.  During coordinated flight, the needle of the turn-and- slip indicator gives an indirect indication of the bank attitude of the helicopter. When the needle is dis- placed from the vertical position, the helicopter is turning in the direction of the displacement. Thus, if the needle is displaced to the left, the helicopter is turning left. Bringing the needle back to the vertical position with the cyclic produces straight flight. A close observation of the needle is necessary to accu- rately interpret small deviations from the desired position. Cross-check the ball of the turn-and-slip indicator to determine that the helicopter is in coordinated flight. If the rotor is laterally level and torque is properly com- pensated for by pedal pressure, the ball remains in the center. To center the ball, level the helicopter laterally by reference to the other bank instruments, then center the ball with pedal trim. Torque correction pressures vary as you make power changes. Always check the ball following such changes. Pitch and bank attitudes can be determined simultane- ously on the attitude indicator. Even though the miniature aircraft is not level with the horizon bar, pitch attitude can be established by observing the relative position of the miniature aircraft and the horizon bar. The attitude indicator may show small misrepresenta- tions of bank attitude during maneuvers that involve turns. This precession error can be immediately detected by closely cross-checking the other bank instruments during these maneuvers. Precession nor- mally is noticed when rolling out of a turn. If, on the completion of a turn, the miniature aircraft is level and COMMON ERRORS DURING STRAIGHT-AND- LEVEL FLIGHT 12-10 1. Failure to maintain altitude. 2. Failure to maintain heading. 3. Overcontrolling pitch and bank during corrections. 4. Failure to maintain proper pedal trim. 5. Failure to cross-check all available instruments. Figure 12-14. The banking scale at the top of the attitude indi- cator indicates varying degrees of bank. In this example, the helicopter is banked a little over 10° to the right. TURN INDICATOR HEADING INDICATOR