indicates the desired heading, simultaneously ensuring the  ball is centered. When making the correction to the desired  heading, do 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 precision 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 displaced 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 accurately  interpret small deviations from the desired position.  Cross-check the ball of the turn-and-slip indicator to  determine if the helicopter is in coordinated flight.  [Figure 8-6]  If the rotor is laterally level and pedal pressure  properly compensates for torque, 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 power  changes are made. Always check the ball after such changes.  Establishing specific power settings is accomplished through  collective pitch adjustments and throttle control, where  necessary. For reciprocating-powered helicopters, power  indication is observed on the manifold pressure gauge.  For turbine-powered helicopters, power is observed on the  torque gauge. (Although most instrument flight rules (IFR)- certified helicopters are turbine powered, depictions within  this chapter use a reciprocating-powered helicopter as this  is where training is most likely conducted.)  At any given airspeed, a specific power setting determines  whether the helicopter is in level flight, in a climb, or in a  descent. For example, cruising airspeed maintained with  cruising power results in level flight. If a pilot increases the  power setting and holds the airspeed constant, the helicopter  climbs. Conversely, if the pilot decreases power and holds  the airspeed constant, the helicopter descends.  Turn Indicator Power Control During Straight-and-Level Flight Common Errors During Straight-and-Level Flight 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  A O M  3  4  I  0  2  2  I  3  VERTICAL SPEED  THOUSAND FT PER MIN  UP  DOWN  .5  .5  33  30  24  2I  I5  I2  6  3  2 MIN TURN  DC ELEC  L R  30.0  29.9  29.8  I 0 0 F E T I  4  5  6  7  9  2  0  8  3  CALIBRATED  TO 20,000 FEET  ALT  20 20  I0 I0 I0 I0 20 20  TEST  STBY PWR  IN Hg ALg. MANIFOLD  PRESS  25 5 15 30 20 10 35 110  100  90  80  70  60  50  110  100  90  80  70  60  50  E R  %RPM  Figure 8-6.  Coordinated flight is indicated by centering of the ball.  8-7