• Attitude Retention Systems (ATT) 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 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) 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  FDs 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 what 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 flightpath or may couple the  autopilot to the FD to fly along the desired flightpath.  Typically, FD 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  instrument landing system (ILS) approach and using  the three-cue mode (lateral, vertical, and collective  cues), the FD 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 two-cue  mode on an ILS, the FD horizontal bar cue responds  to glideslope deviations. The need to be aware of the  FD mode of operation is particularly significant when  operating using two pilots.  •  Minimum equipment required for IFR flight (in some  cases, for both single-pilot and two-pilot operations)  •  V$_{MINI}$ (minimum speed—IFR) [Figure 7-2]  •  V$_{NEI}$ (never exceed speed—IFR)  •  Maximum approach angle  •  Weight and center of gravity (CG) limits  •  Helicopter configuration limitations (such as door  positions and external loads)  •  Helicopter system limitations (generators, inverters,  etc.)  •  System testing requirements (many avionics and AFCS,  AP, and FD systems incorporate a self-test feature)  •  Pilot action requirements (for example, the pilot must  have hands and feet on the controls during certain  operations, such as an instrument approach below  certain altitudes)  Pilots should have an established set of procedures and  responsibilities for the control of FD/AP 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.  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  additional equipment is required for single-pilot operation.  In addition, the Helicopter Flight Manual (HFM) defines  systems and functions that are required to be in operation  or engaged for IFR flight in either the single or two-pilot  configurations. Often, in a two-pilot operation, this level of  augmentation is less than the full capability of the installed  systems. Likewise, a single-pilot operation may require a  higher level of augmentation.  The HFM also identifies other specific limitations associated  with IFR flight. Typically, these limitations include, but are  not limited to:  Final approach angles/descent gradient for public  approach procedures can be as high as 7.5 degrees/795  ft/NM. At 70 knots indicated airspeed (KIAS) (no wind),  this equates to a descent rate of 925 fpm. With a 10-knot  tailwind, the descent rate increases to 1,056 fpm. “Copter”  Point-in-space (PinS) approach procedures are restricted  to helicopters with a maximum V$_{MINI}$ of 70 KIAS and an  IFR approach angle that enables them to meet the final  approach angle/descent gradient. Pilots of helicopters with  7-3  Helicopter Flight Manual Limitations 