ease the pilot's workload, a mechanical throttle correlator adjusts the throttle as the collective pitch control is raised or lowered. The pilot needs to make only small adjustments by twisting the throttle grip on the collective throughout the flight regimen. Later models are also equipped with an electronic governor, which works to maintain engine speed within normal operating limits (between 97 and 104%); the governor is active when the engine is running only above 80% of socified speed, and is most effective in normal flight conditions. The governor can be switched on or off with a toggle switch located at the end of the pilot's collective pitch control. When the governor is not engaged, a yellow caution light glows on the instrument panel. Powerplant The R22 uses a horizontally mounted Lycoming O-320 (O-360-J2A on the Beta II), flat-four, air-cooled, normally aspirated, carburetor-equipped, reciprocating engine. It is fueled with 100LL grade aviation gasoline. Cooling is provided through a direct-drive, squirrel-cage cooling fan. At sea level, it is derated, or operated at less than maximum power, which has been attributed to the company wishing for the power unit to maintain the same performance at sea level as it does at altitude. As the air becomes thinner with increasing altitude, maximum available horsepower decreases, reaching a point where the throttle can be completely open and rotor speed is controlled by collective lever position. By derating the engine at sea level, the R22 achieves acceptable high-altitude performance without use of supercharging or turbocharging, thus saving the weight, cost, complexity, unreliability, and shortened engine life of a forced induction system. A carburetor is used to provide the air-fuel mixture. Carbureted engines are susceptible to carburetor icing, a condition most likely to occur in conditions of a low 11 °C (20 °F) difference between the outside air temperature and dew point (the "dew point spread"), as well as visible signs of moisture in the atmosphere. Icing can lead to loss of engine power, and if not corrected, total shutdown of the engine. A carburetor heat control is used to supply heated air to the carburetor; this can prevent or cure icing, but also causes a reduction in engine power output because hot air is less dense, enriching the fuel-air mixture. The carburetor heat control is a simple plunger-type control mounted on the center console near the collective pitch control lever. Pulling the control up slides a