Aviation Frequency Guide
Understanding the different types of radio frequencies used in aviation communications.
Primary Frequency Types
ATIS
Automatic Terminal Information Service
Continuous broadcast of recorded information containing essential operational information for arriving and departing aircraft. Identified by a phonetic letter code (Alpha, Bravo, etc.) that changes with each update.
Larger airports may have separate Arrival ATIS and Departure ATIS frequencies.
TWR
Tower
Controls aircraft operating on the runways and in the vicinity of the airport. Tower controllers issue takeoff and landing clearances and manage the traffic flow in the airport's immediate airspace.
GND
Ground
Controls aircraft and vehicle movements on the airport's taxiways and aprons (but not the active runways). Ground controllers issue taxi instructions and manage the flow of traffic on the ground.
APP
Approach
Controls aircraft approaching an airport, typically within about 30–50 nautical miles. Approach controllers sequence arriving aircraft, issue approach clearances, and provide separation from other traffic.
DEP
Departure
Controls aircraft departing from an airport. Departure controllers ensure separation between departing aircraft and guide them to their en-route airways.
CLD/DEL
Clearance Delivery
Issues IFR (Instrument Flight Rules) clearances and departure instructions to aircraft before they taxi. At busy airports, this service helps reduce frequency congestion on Ground and Tower frequencies.
CTAF
Common Traffic Advisory Frequency
Used at non-towered or part-time towered airports for pilots to coordinate their movements with each other. Pilots announce their positions and intentions on this frequency.
UNICOM
Universal Communications
Non-government air/ground radio communication station that may provide airport information at public use airports where there is no tower or Flight Service Station. Often operated by the airport's Fixed Base Operator (FBO).
FSS
Flight Service Station
Provides information services such as weather briefings, flight plan filing, and can relay ATC clearances. Flight Service Stations also monitor emergency frequencies.
CNTR/CTR
Center
Air Route Traffic Control Center (ARTCC) that controls aircraft in the en-route phase of flight at higher altitudes between terminal areas. Center controllers provide separation between aircraft and route them efficiently.
AWOS/ASOS
Automated Weather Observing/Surface Observing System
Automated systems that provide continuous weather reports at airports, broadcasting on their dedicated frequencies. They report wind, visibility, cloud coverage, temperature, and more.
RDO
Radio
General designation for radio communications facilities. May include company frequencies or specialized communications stations.
Typical Frequency Sequence for a Departure
When departing a controlled airport IFR, pilots typically work through these frequencies in order:
- 1
Obtain the ATIS
Before contacting ATC, listen to the ATIS (Automatic Terminal Information Service) to get current airport conditions and the active information code.
- 2
Contact Clearance Delivery (IFR)
If flying IFR, contact Clearance Delivery (CLD/DEL) to receive your IFR clearance before taxiing.
- 3
Contact Ground Control
Request taxi clearance from Ground Control (GND) to move from the ramp to the runway.
- 4
Switch to Tower
When instructed, switch to Tower (TWR) frequency for takeoff clearance.
- 5
Contact Departure
After takeoff, Tower will hand you off to Departure Control (DEP) for climb-out instructions.
- 6
En Route with Center
Departure will hand you off to Center (CNTR/CTR) for en-route ATC services.
Additional Frequency Types
AFIS
Aerodrome Flight Information Service
Provides information to aircraft at smaller airports without ATC.
MULTICOM
Multicom
Used for air-to-air communications between aircraft, often at uncontrolled airports.
RADAR
Radar
Radar control services, often specialized by region or function.
GCA
Ground Controlled Approach
Precision approach radar system, common at military airfields.
OPS
Operations
Frequencies for airport operations, maintenance, and management.
APRON
Apron
Controls aircraft parking and movements in the apron/ramp areas.
EMERGENCY
Emergency
Emergency frequencies — 121.5 MHz is the international air distress frequency.
VOLMET
Volmet
Continuous broadcast of meteorological information for aircraft in flight.