instrument only long enough to understand the information  it presents, and then proceed to the next one. Similarly, too  much emphasis can be placed on a single instrument, instead  of relying on a combination of instruments necessary for  helicopter performance information. This differs from fixation  in that other instruments are included in a cross-check, but too  much attention is placed on one particular instrument.  During performance of a maneuver, there is sometimes  a failure to anticipate significant instrument indications  following attitude changes. For example, during level off  from a climb or descent, a pilot may concentrate on pitch  control, while forgetting about heading or roll information.  This error, called omission, results in erratic control of  heading and bank.  In spite of these common errors, most pilots can adapt well to  flight by instrument reference after instruction and practice.  Many find that they can control the helicopter more easily  and precisely by instruments.  The flight instruments together give a picture of what is  happening. No one instrument is more important than the  next; however, during certain maneuvers or conditions,  those instruments that provide the most pertinent and useful  information are termed primary instruments. Those which  back up and supplement the primary instruments are termed  supporting instruments. For example, since the attitude  indicator is the only instrument that provides instant and  direct aircraft attitude information, it should be considered  primary during any change in pitch or bank attitude. After  the new attitude is established, other instruments become  primary, and the attitude indicator usually becomes the  supporting instrument.  Controlling a helicopter is the result of accurately interpreting  the flight instruments and translating these readings  into correct control responses. Aircraft control involves  adjustment to pitch, bank, power, and trim in order to achieve  a desired flight path.  Pitch attitude control is controlling the movement of  the helicopter about its lateral axis. After interpreting  the helicopter’s pitch attitude by reference to the pitch  instruments (attitude indicator, altimeter, airspeed  indicator, and vertical speed indicator (VSI)), cyclic control  adjustments are made to affect the desired pitch attitude. In  this chapter, the pitch attitudes depicted are approximate  and vary with different helicopters.  Bank attitude control is controlling the angle made by the  lateral tilt of the rotor and the natural horizon or the movement  of the helicopter about its longitudinal axis. After interpreting  the helicopter’s bank instruments (attitude indicator, heading  indicator, and turn indicator), cyclic control adjustments are  made to attain the desired bank attitude.  Power control is the application of collective pitch with  corresponding throttle control, where applicable. In straight- and-level flight, changes of collective pitch are made to  correct for altitude deviation if the error is more than 100  feet or the airspeed is off by more than 10 knots. If the error  is less than that amount, a pilot should use a slight cyclic  climb or descent.  In order to fly a helicopter by reference to the instruments, it  is important to know the approximate power settings required  for a particular helicopter in various load configurations and  flight conditions.  Trim, in helicopters, refers to the use of the cyclic centering  button, if the helicopter is so equipped, to relieve all  possible cyclic pressures. Trim also refers to the use of pedal  adjustment to center the ball of the turn indicator. Pedal trim  is required during all power changes.  The proper adjustment of collective pitch and cyclic friction  helps a pilot relax during instrument flight. Friction should  be adjusted to minimize overcontrolling and to prevent  creeping, but not applied to such a degree that control  movement is limited. In addition, many helicopters equipped  for instrument flight contain stability augmentation systems  or an autopilot to help relieve pilot workload.  Straight-and-level unaccelerated flight consists of maintaining  the desired altitude, heading, airspeed, and pedal trim.  The pitch attitude of a helicopter is the angular relation of  its longitudinal axis to the natural horizon. If available, the  attitude indicator is used to establish the desired pitch attitude.  In level flight, pitch attitude varies with airspeed and center of  gravity (CG). At a constant altitude and a stabilized airspeed,  the pitch attitude is approximately level.  [Figure 8-2]  The attitude indicator gives a direct indication of the pitch  attitude of the helicopter. In visual flight, attain the desired  pitch attitude by using the cyclic to raise and lower the nose  Pitch Control Straight-and-Level Flight Attitude Indicator Aircraft Control Instrument Interpretation 8-3