FIG ENR 5.7.3
Plumes
Federal Aviation Administration Twentieth Edition
ENR 6. Helicopter Operations
ENR 6.1 Helicopter IFR Operations
1. Helicopter Flight Control Systems
1.1 The certification requirements for helicopters to operate under Instrument Flight Rules (IFR) are contained in 14 CFR Part 27, Airworthiness Standards: Normal Category Rotorcraft, and 14 CFR Part 29, Airworthiness Standards: Transport Catego-ry Rotorcraft. To meet these requirements, helicopter manufacturers usually utilize a set of stabilization and/or Automatic Flight Control Systems (AFCSs).
1.2 Typically, these systems fall into the following categories:
1.2.1 Aerodynamic surfaces, which impart some stability or control capability not found in the basic VFR configuration.
1.2.2 Trim systems, which provide a cyclic centering effect. These systems typically involve a magnetic brake/spring device, and may also be controlled by a four.way switch on the cyclic. This is a system that supports “hands on” flying of the helicopter by the pilot.
1.2.3 Stability Augmentation Systems (SASs), which provide short.term rate damping control inputs to increase helicopter stability. Like trim systems, SAS supports “hands on” flying.
1.2.4 Attitude Retention Systems (ATTs), which return the helicopter to a selected attitude after a disturbance. Changes in desired attitude can be accomplished usually through a four.way “beep” switch, or by actuating a “force trim” switch on the cyclic, setting the attitude manually, and releasing. Attitude retention may be a SAS function, or may be the basic “hands off” autopilot function.
1.2.5 Autopilot Systems (APs), which provide for “hands off” flight along specified lateral and vertical paths, including heading, altitude, vertical speed, navigation tracking, and approach. These systems typically have a control panel for mode selection, and system for indication of mode status. Autopilots may or may not be installed with an associated Flight Director System (FD). Autopilots typically control the helicopter about the roll and pitch axes (cyclic control) but may also include yaw axis (pedal control) and collective control servos.
1.2.6 FDs, which provide visual guidance to the pilot to fly specific selected lateral and vertical modes of operation. The visual guidance is typically provided as either a “dual cue” (commonly known as a “cross.pointer”) or “single cue” (commonly known as a “vee.bar”) presentation superimposed over the attitude indicator. Some FDs also include a collective cue. The pilot manipulates the helicopter’s controls to satisfy these commands, yielding the desired flight path, or may couple the flight director to the autopilot to perform automatic flight along the desired flight path. Typically, flight director mode control and indication is shared with the autopilot.
1.3 In order to be certificated for IFR operation, a specific helicopter may require the use of one or more of these systems, in any combination.
1.4 In many cases, helicopters are certificated for IFR operations with either one or two pilots. Certain equipment is required to be installed and functional for two pilot operations, and typically, additional equipment is required for single pilot operation. These requirements are usually described in the limitations section of the Rotorcraft Flight Manual (RFM).
1.5 In addition, the RFM also typically defines systems and functions that are required to be in operation or engaged for IFR flight in either the single or two pilot configuration. Often, particularly in two pilot operation, this level of augmentation is less than the full capability of the installed systems. Likewise, single pilot operation may require a higher level of augmentation.
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