igation capabilities, such as VOR, ILS, and GPS intercept and tracking, which is especially useful in IFR conditions. The most advanced autopilots can fly an instrument approach to a hover without any additional pilot input once the initial functions have been selected. servos, on each flight control, a pump which is usually driven by the main rotor gearbox, and a reservoir to store the hydraulic fluid. A switch in the cockpit can turn the system off, although it is left on under normal conditions. A pressure indicator in the cockpit may also be installed to monitor the system. When you make a control input, the servo is activated and provides an assisting force to move the respective flight control, thus lightening the force required by the pilot. These boosted flight controls ease pilot workload and fatigue. In the event of hydraulic system failure, you are still able to control the helicopter, but the con- trol forces will be very heavy. 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 anti- torque 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 con- trols when they receive control commands from a cen- tral 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 cock- pit that allows you to select the desired functions, as well as engage the autopilot. In those helicopters where the control forces are so high that they cannot be moved without hydraulic assistance, two or more independent hydraulic systems may be installed. Some helicopters use hydraulic accu- mulators to store pressure, which can be used for a short period of time in an emergency if the hydraulic pump fails. This gives you enough time to land the hel- icopter with normal control For safety purposes, an automatic disengage 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 disen- gage button located on the cyclic or collective which allows you to completely disengage the autopilot with- out removing your hands from the controls. Because autopilot systems and installations differ from one hel- icopter to another, it is very important that you refer to the autopilot operating procedures located in the Rotorcraft Flight Manual.  Some helicopters incorporate stability augmentations systems (SAS) to aid in stabilizing the helicopter in flight and in a hover. The simplest of these systems is a force trim system, which uses a magnetic clutch and springs to hold the cyclic control in the position where it was released. More advanced systems use electric servos that actually move the flight controls. These servos receive control commands from a computer that senses helicopter attitude. Other inputs, such as heading, speed, altitude, and navigation information may be supplied to the computer to form a complete autopilot system. The SAS may be overridden or disconnected by the pilot at any time.  Heating and cooling for the helicopter cabin can be provided in different ways. The simplest form of cool- ing is ram air cooling. 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 Stability augmentation systems reduce pilot workload by improving basic aircraft control harmony and decreasing disturbances. These systems are very useful when you are required to perform other duties, such as sling loading and search and rescue operations. Helicopter autopilot systems are similar to stability augmentations systems except 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.  VOR—Ground-based navigation system consisting of very high fre- quency omnidirectional range (VOR) stations which provide course guidance. ILS (Instrument Landing System)—A precision instrument approach system, which normally consists of the following electronic components and visual aids: localizer, glide slope, outer marker, and approach lights. GPS (Global Positioning System)—A satellite-based radio positioning, navigation, and time-transfer system.  IFR (Instrument Flight Rules)—Rules that govern the procedure for conducting flight in weather conditions below VFR weather minimums. The term IFR also is used to define weather conditions and the type of flight plan under which an aircraft is operating. 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 indicated airspeed is maintained by the autopilot. Some autopilots have nav- 5-10 AUTOPILOT ENVIRONMENTAL SYSTEMS STABILITYAUGMENTATIONS SYSTEMS