Altimeter and turn indicator readings should remain constant  throughout the turn. The altimeter is primary for pitch control,  and the turn needle is primary for bank control. Manifold  pressure is primary for power control while the airspeed is  changing. As the airspeed approaches the new indication, the  airspeed indicator becomes primary for power control.  Two methods of changing airspeed in turns may be used.  In the first method, airspeed is changed after the turn is  established. In the second method, the airspeed change  is initiated simultaneously with the turn entry. The first  method is easier, but regardless of the method used, the rate  of cross-check must be increased as power is reduced. As  the helicopter decelerates, check the altimeter and VSI for  needed pitch changes and the bank instruments for needed  bank changes. If the needle of the turn-and-slip indicator  shows a deviation from the desired deflection, change the  bank. Adjust pitch attitude to maintain altitude. When the  airspeed approaches that desired, the airspeed indicator  becomes primary for power control. Adjust the power to  maintain the desired airspeed. Use pedal trim to ensure the  maneuver is coordinated.  Until control technique is very smooth, frequently cross- check the attitude indicator to keep from overcontrolling  and to provide approximate bank angles appropriate for the  changing airspeeds.  The use of gyroscopic heading indicators makes heading  control very easy. However, if the heading indicator fails  or the helicopter is not equipped with one, use the magnetic  compass for heading reference. When making compass-only  turns, a pilot needs to adjust for the lead or lag created by  acceleration and deceleration errors so that the helicopter rolls  out on the desired heading. When turning to a heading of north,  the lead for the roll-out must include the number of degrees  of latitude plus the lead normally used in recovery from turns.  During a turn to a south heading, maintain the turn until the  compass passes south the number of degrees of latitude, minus  the normal roll-out lead. For example, when turning from an  easterly direction to north, where the latitude is 30°, start the  roll-out when the compass reads 37° (30° plus one-half the  15° angle of bank or whatever amount is appropriate for the  rate of roll-out). When turning from an easterly direction to  south, start the roll-out when the magnetic compass reads  203° (180° plus 30° minus one-half the angle of bank). When  making similar turns from a westerly direction, the appropriate  points at which to begin the roll-out would be 323° for a turn  to north and 157° for a turn to south.  For climbing and descending turns, the techniques described  previously for straight climbs, descents, and standard rate  turns are combined. For practice, simultaneously turn and  start the climb or descent. The primary and supporting  instruments for a stabilized constant airspeed left climbing  turn are illustrated in  Figure 8-15 . The level off from a  climbing or descending turn is the same as the level off from  a straight climb or descent. To return to straight-and-level  flight, stop the turn and then level off, or level off and then  stop the turn, or simultaneously level off and stop the turn.  During climbing and descending turns, keep the ball of the  turn indicator centered with pedal trim.  A turn using 30° of bank is seldom necessary or advisable  in instrument meteorological conditions (IMC) and is  considered an unusual attitude in a helicopter. However, it  is an excellent maneuver to practice to increase the ability to  react quickly and smoothly to rapid changes of attitude. Even  though the entry and recovery techniques are the same as for  any other turn, it is more difficult to control pitch because  of the decrease in vertical lift as the bank increases. Also,  because of the decrease in vertical lift, there is a tendency  to lose altitude and/or airspeed. Therefore, to maintain a  constant altitude and airspeed, additional power is required.  Do not initiate a correction, however, until the instruments  indicate the need for one. During the maneuver, note the  need for a correction on the altimeter and VSI, check the  attitude indicator, and then make the necessary adjustments.  After making a change, check the altimeter and VSI again  to determine whether or not the correction was adequate.  30° Bank Turn Climbing and Descending Turns Compass Turns Common Errors During Turns 1.  Failure to maintain desired turn rate  2.  Failure to maintain altitude in level turns  3.  Failure to maintain desired airspeed  4.  Variation in the rate of entry and recovery  5.  Failure to use proper lead in turns to a heading  6.  Failure to properly compute time during timed turns  7.  Failure to use proper leads and lags during the  compass turns  8.  Improper use of power  9.  Failure to use proper pedal trim  8-15