An aircraft station license is what the FCC (Federal Communications Commission) requires a pilot to have in order to operate a radio transmitter from inside the plane. The main reason for this is so the FCC can keep track of and authorize the use of different, specific frequencies for all usage. The FCC discourages pilots from using their radios any more than they have to, because the less time each pilot is on the airwaves, the less likely it is that the frequencies will interfere with each other. In the event that a pilot with a United States pilot with an FCC aircraft station license is overseas, he is authorized by the FCC to use different frequencies, so long as this is compliant with the regulations of the foreign country. Other extenuating circumstances include the permissible use of frequency 121.5 MHz, which is allowed for emergencies and distress calls only. Most pilots with higher than a light sport license (such as private pilots and commercial pilots) should have an aircraft station license so that they may operate their plane's radio transmitter.