- FSS Flight Service Station provide info and services to aircraft but unlike ATC is not responsible for giving instructions, clearances or providing separation
- ATC Air Traffic Control is service by ground based controllers who direct aircraft through controlled airspace and can provide advisory services to aircraft in non-controlled airspace.
- CTAF Common Traffic Advisory Frequency is a radio frequency used to coordinate air traffic at an airport. Usually refer to frequencies at airports without operating control tower. (if tower > ATC frequency is the CTAF, otherwise CTAF is used by pilots to advise their actions or intentions.
- UNICOM is a private licensed ground base station that can communicate with a aircraft at airports with no tower or FSS.
