Environmental Systems Autopilot computer. This computer receives data input from the flight  instruments for attitude reference and from the navigation  equipment for navigation and tracking reference. An autopilot  has a control panel in the cockpit that allows the pilot to  select the desired functions, as well as engage the autopilot. For safety purposes, an automatic disengagement feature  is usually included which automatically disconnects the  autopilot in heavy turbulence or when extreme flight attitudes  are reached. Even though all autopilots can be overridden  by the pilot, there is also an autopilot disengagement button  located on the cyclic or collective which allows pilots to  completely disengage the autopilot without removing their  hands from the controls. Because autopilot systems and  installations differ from one helicopter to another, it is very  important to refer to the autopilot operating procedures  located in the RFM. Once engaged by the pilot, these actual systems use a  multitude of sensors, from stabilized gyros to electro- mechanical actuators, which provide instantaneous inputs  to all flight controls without pilot assistance. As with all  SASs, they may be overridden or disconnected by the pilot  at any time. Helicopters with complex Automatic Flight  Control Systems (AFCS) and autopilots normally have  a trim switch referred to as “beeper trim.” This switch is  used when minor changes to the trim setting are desired. Stability augmentation systems reduce pilot workload by  improving basic aircraft control harmony and decreasing  disturbances. These systems are very useful when the pilot  is required to perform other duties, such as sling loading and  search-and-rescue operations. Other inputs such as heading,  speed, altitude, and navigation information may be supplied  to the computer to form a complete autopilot system. Helicopter autopilot systems are similar to stability  augmentation systems, but they have additional features. An  autopilot can actually fly the helicopter and perform certain  functions selected by the pilot. These functions depend on  the type of autopilot and systems installed in the helicopter. Heating and cooling the helicopter cabin can be accomplished  in different ways. The simplest form of cooling is by ram air.  Air ducts in the front or sides of the helicopter are opened or  closed by the pilot to let ram air into the cabin. This system  is limited as it requires forward airspeed to provide airflow  and also depends on the temperature of the outside air. Air  conditioning provides better cooling, but it is more complex  and weighs more than a ram air system.  The most common functions are altitude and heading hold.  Some more advanced systems include a vertical speed or  indicated airspeed (IAS) hold mode, where a constant rate  of climb/descent or IAS is maintained by the autopilot. Some  autopilots have navigation capabilities, such as very high  frequency (VHF) OmniRange Navigation System (VOR),  Instrument Landing System (ILS), and global positioning  system (GPS) intercept and tracking, which is especially  useful in instrument flight rules (IFR) conditions. This is  referred to as a coupled system. An additional component,  called a flight director (FD), may also be installed. The FD  provides visual guidance cues to the pilot to fly selected  lateral and vertical modes of operation. The most advanced  autopilots can fly an instrument approach to a hover without  any additional pilot input once the initial functions have  been selected. One of the simplest methods of cooling a helicopter is to  remove the doors allowing air to flow through the cockpit  and engine compartments. Care must be taken to store the  doors properly, whether in a designed door-holding rack in  a hangar, or if it is necessary to carry them on the flight, in  the helicopter. When storing the doors, care must be taken  to not scratch the windows. Special attention should be paid  to ensuring that all seat belt cushions and any other loose  items are stored away to prevent ingestion into the main or  tail rotor. When reattaching the doors, proper care must be  taken to ensure that they are fully secured and closed.  Air conditioners or heat exchanges can be fitted to the  helicopter as well. They operate by drawing bleed air from  the compressor, passing it through the heart exchanger and  then releasing it into the cabin. As the compressed air is  released, the expansion absorbs heat and cools the cabin. The  disadvantage of this type of system is that power is required  to compress the air or gas for the cooling function, thus  robbing the engine of some of its capability. Some systems  are restricted from use during takeoff and landings. The autopilot system consists of electric actuators or servos  connected to the flight controls. The number and location of  these servos depends on the type of system installed. A two- axis autopilot controls the helicopter in pitch and roll; one  servo controls fore and aft cyclic, and another controls left  and right cyclic. A three-axis autopilot has an additional servo  connected to the antitorque pedals and controls the helicopter  in yaw. A four-axis system uses a fourth servo which controls  the collective. These servos move the respective flight  controls when they receive control commands from a central  4-18