aircraft at a certain attitude. This allows more time to devote  to the navigation instruments and additional flight deck duties.  An aircraft is placed in trim by: A helicopter is placed in trim by continually cross-checking  the instruments and performing the following:  An improperly trimmed helicopter requires constant control  pressures, produces tension, distracts attention from cross- checking, and contributes to abrupt and erratic attitude  control. The pressures felt on the controls should be only  those applied while controlling the helicopter.  Adjust the pitch attitude, as airspeed changes, to maintain  desired attitude for the maneuver being executed. The bank  must be adjusted to maintain a desired rate of turn, and the  pedals must be used to maintain coordinated flight. Trim must  be adjusted as control pressures indicate a change is needed. Straight-and-level flight at a constant airspeed means that an  exact altitude is to be maintained with zero bank (constant  heading). The primary pitch, bank, and power instruments  used to maintain this flight condition are:  Cross-checking is mandatory in instrument flying. In  visual flight, a level attitude can be maintained by outside  references. However, even then the altimeter must be checked  to determine if altitude is being maintained. Due to human  error, instrument error, and airplane performance differences  in various atmospheric and loading conditions, it is impossible  to establish an attitude and have performance remain constant  The first fundamental skill is cross-checking (also called  “scanning” or “instrument coverage”). Cross-checking is the  continuous and logical observation of instruments for attitude  and performance information. In attitude instrument flying,  the pilot maintains an attitude by reference to instruments,  producing the desired result in performance. Observing and  interpreting two or more instruments to determine attitude and  performance of an aircraft is called cross-checking. Although  no specific method of cross-checking is recommended, those  instruments that give the best information for controlling the  aircraft in any given maneuver should be used. The important  instruments are the ones that give the most pertinent  information for any particular phase of the maneuver. These  are usually the instruments that should be held at a constant  indication. The remaining instruments should help maintain  the important instruments at the desired indications, which  is also true in using the emergency panel. During attitude instrument training, two fundamental flight  skills must be developed. They are instrument cross-check  and instrument interpretation, both resulting in positive  aircraft control. Although these skills are learned separately  and in deliberate sequence, a measure of proficiency in  precision flying is the ability to integrate these skills into  unified, smooth, positive control responses to maintain any  prescribed flightpath. Although the attitude indicator is the basic attitude reference,  the concept of primary and supporting instruments does not  devalue any particular flight instrument, when available, in  establishing and maintaining pitch-and-bank attitudes. It is the  only instrument that instantly and directly portrays the actual  flight attitude. It should always be used, when available, in  establishing and maintaining pitch-and-bank attitudes. The  specific use of primary and supporting instruments during  basic instrument maneuvers is presented in more detail in  Chapter 7, Airplane Basic Flight Maneuvers.  •  Heading Indicator—supplies the most pertinent bank  or heading information and is primary for bank.   •  Airspeed Indicator—supplies the most pertinent  information concerning performance in level flight  in terms of power output and is primary for power.  •  Applying control pressure(s) to establish a desired  attitude. Then, the trim is adjusted so that the aircraft  maintains that attitude when flight controls are  released. The aircraft is trimmed for coordinated flight  by centering the ball of the turn-and-slip indicator.  •  Moving the rudder trim in the direction where the  ball is displaced from center. Aileron trim may then  be adjusted to maintain a wings-level attitude.  •  Using balanced power or thrust when possible to aid  in maintaining coordinated flight. Changes in attitude,  power, or configuration may require trim adjustments.  Use of trim alone to establish a change in aircraft  attitude usually results in erratic aircraft control.  Smooth and precise attitude changes are best attained  by a combination of control pressures and subsequent  trim adjustments. The trim controls are aids to smooth  aircraft control. •  Using the cyclic-centering button. If the helicopter is  so equipped, this relieves all possible cyclic pressures.  •  Using the pedal adjustment to center the ball of the  turn indicator. Pedal trim is required during all power  changes and is used to relieve all control pressures  held after a desired attitude has been attained.  •  Altimeter—supplies the most pertinent altitude  information and is primary for pitch.  Example of Primary and Support Instruments Instrument Cross-Check Fundamental Skills Helicopter Trim 6-10