Unless a pilot is operating under a light sport aircraft license, he is likely to require the use of a radio, and this may necessitate an aircraft radio station license. There are two sides to aircraft radio station usage: the pilot and the traffic control tower (or sometimes the pilot of other aircraft). Any pilot who is flying in a higher class of airspace should be tuned in to the frequency of his licensed aircraft radio station so that important information can reach him and he can communicate with others if need be. The Federal Communications Commission (FCC) regulates the use of radio frequencies in the United States, and anyone who is using a frequency must have that frequency registered with and authorized by the FCC. The rules regarding radio station usage basically are that a pilot should have an aircraft radio station license to operate the radio transmitter in his aircraft. This is so the frequencies can be as clear as possible. Radio users are suggested to limit their messages to only the essentials. In emergencies, the frequency 121.5 MHz is used. As a general rule of thumb, anyone with a private pilot license or higher should be registered for an aircraft radio station license.