There are three types of communications systems used in  WSC aircraft:  Easy and clear communications between the pilot and  passenger, or between the instructor and student inside  the flight deck is important for the safety and enjoyment  of both. Modern communications systems have advanced  noise canceling systems in headphones and microphones to  reduce engine noise and blast of air. Each system is unique,  and the quality of the sound and noise canceling capability  of the system varies. Some use voice-activated systems in  which headphones activate only when someone is speaking  into the microphone; others have a steady state in which  there is no additional control of the voice activation. Since  there is a large difference in systems available, it is best to  test systems to determine what is best for the WSC aircraft  being fl own.  [Figure 3-48] An aircraft radio is required for flying in any tower controlled  airspace. Using a radio is not required at airports without a  control tower but it is recommended for the safety of self,  passengers, pilots in the air, and people/property on the  ground. To broadcast to a tower or other aircraft, press a  Push To Talk (PTT) button. A complete flight deck radio and  accessory system schematic is shown in  Figure 3-49 . The powerplant system is composed of the fuel system,  engine, gearbox, and propeller. Here we will point out the  basic components of these systems with their function and  details covered in Chapter 4, Powerplant System. A radar signal receiver/transmitter system is required at busy  commercial airports (Classes C and B) and at altitudes above  10,000 feet mean sea level (MSL) (unless the aircraft was  certified without an electrical system to power the unit). This  is known as a Mode C transponder that sends a signal giving  the control tower an exact location and altitude of aircraft.  [Figure 3-47] 1.  Communications between the pilot and passenger  while inside the aircraft.  2.  Aircraft radio communications with other aircraft and  control towers.  3.  Radar position indicator communications from the  WSC aircraft to control towers (transponder).  Some systems require an intercom  box for headphones to plug into. O F F$^{2}$ 1 Hea d Phone  2 Hea d Phone  1 H e$_{ad}$ $^{ Ph}$o n e s Battery Head Phone 2— Passenger Head Phone 1—Pilot P.T.T. 1—Push To Talk P.T.T. 2 (optional) used for  instructor  during training Head phones disconnect Radio Fuse Optional Device music or cell phone Figure 3-49. Flight deck and aircraft radio communications system example. Figure 3-48. Basic pilot-to-passenger communication system.  Powerplant System   Communications  3-19