MISCELLANEOUS REQUIREMENTS

• Overvoltage disconnect.
• Instrument power source indicator.
• Adequate ice protection of IFR systems.

• Alternate static source (single pilot configuration).
• Thunderstorm lights (transport category helicopters).

STABILIZATION AND AUTOMATIC FLIGHT CONTROL SYSTEM (AFCS)

Helicopter manufacturers normally use a combination of a stabilization and/or AFCS in order to meet the IFR stability requirements of Parts 27 and 29. These systems include:

• Aerodynamic surfaces, which impart some stability or control capability that generally is not found in the basic VFR configuration.
• Trim systems, which provide a cyclic centering effect. These systems typically involve a magnetic brake/spring device, and may be controlled by a four-way switch on the cyclic. This system supports “hands on” flying of the helicopter.
• SStability Augmentation Systems (SASs), which provide short-term rate damping control inputs to increase helicopter stability. Like trim systems, SAS supports “hands on” flying.
• Attitude Retention Systems (ATTs), which return the helicopter to a selected attitude after a disturbance. Changes in attitude can be accomplished usually through a four-way “beep” switch, or by actuating a “force trim” switch on the cyclic, which sets the desired attitude manually. Attitude retention may be a SAS function, or may be the basic “hands off” autopilot function.
• Autopilot Systems (APs) provide for “hands off” flight along specified lateral and vertical paths. The functional modes may include heading, altitude, vertical speed, navigation tracking, and approach. APs typically have a control panel for mode selection and indication of mode status. APs may or may not be installed with an associated flight director (FD). APs typically control the helicopter about the roll and pitch axes (cyclic control) but may also include yaw axis (pedal control) and collective control servos.
• Flight Directors (FDs), which provide visual guidance to the pilot to fly selected lateral and vertical modes of operation. The visual guidance is typically provided by a “single cue,” commonly known as a “vee bar,” which provides the indicated attitude to fly and is superimposed on the attitude indicator. Other flight directors may use a “two cue” presentation known as a “cross pointer system.” These two presentations only provide attitude information. A third system, known as a “three cue” system, provides information to position the collective as well as attitude (roll and pitch) cues. The collective control cue system identifies and cues the pilot which collective control inputs to use when path errors are produced, or when airspeed errors exceed preset values. The three-cue system pitch command provides the required cues to control airspeed when flying an approach with vertical guidance at speeds slower than the best-rate-of-climb (BROC) speed. The pilot manipulates the helicopter’s controls to satisfy these commands, yielding the desired flight path, or may couple the autopilot to the flight director to fly along the desired flight path. Typically, flight director mode control and indication are shared with the autopilot.
  

Pilots must be aware of the mode of operation of the augmentation systems, and the control logic and functions in use. For example, on an ILS approach and using the three-cue mode (lateral, vertical and collective cues), the flight director collective cue responds to glideslope deviation, while the horizontal bar cue of the "cross-pointer" responds to airspeed deviations. However, the same system when operated in the twocue mode on an ILS, the flight director horizontal bar cue responds to glideslope deviations. The need to be aware of the flight director mode of operation is particularly significant when operating using two pilots. Pilots should have an established set of procedures and responsibilities for the control of flight director/autopilot modes for the various phases of flight. Not only does a full understanding of the system modes provide for a higher degree of accuracy in control of the helicopter, it is the basis for crew identification of a faulty system.