The Toolbox — Frequencies

Aviation Frequencies

VHF airband, VOR/ILS navigation, transponder, ATIS/ASOS/AWOS, military aviation, and emergency frequencies.

VHF Airband (108–136 MHz)

Frequency / Range	Use	Notes
108.000–117.950 MHz	VOR navigation / ILS localizer	Odd tenths only for ILS localizer (108.10–111.95 MHz)
118.000–121.400 MHz	ATC communications	Tower, ground, clearance delivery
121.500 MHz	Emergency / Guard	International distress — monitor continuously
121.600–121.900 MHz	Ground control / clearance	Varies by airport
122.000 MHz	Formerly Flight Watch (EFAS)	Flight Watch was discontinued in 2015; contact FSS on the frequencies shown on charts
122.700 MHz	UNICOM / CTAF	One of several UNICOM frequencies used at non-towered airports
122.750 MHz	Air-to-air	VFR advisory, air-to-air communication
122.800 MHz	UNICOM	General aviation UNICOM
122.900 MHz	MULTICOM	Crop dusters, aerial work, balloons
122.950 MHz	UNICOM	UNICOM at airports with a full-time control tower or FSS
123.000 MHz	UNICOM	UNICOM at non-towered airports
123.025–123.075 MHz	Helicopter operations
123.100 MHz	SAR auxiliary	Search and rescue auxiliary
123.300 MHz	Aviation instruction / gliders / balloons
123.450 MHz	Air-to-air	Common air-to-air frequency
123.500 MHz	Aviation instruction / gliders / balloons
124.000–135.975 MHz	ATC Approach / Departure / Center	Varies by facility and sector
136.000–136.875 MHz	ATC / ACARS	ACARS data link for airline operations

System	Frequency	Notes
VOR	108.000–117.950 MHz	108.00–111.85 even tenths are VOR (odd tenths are ILS); 112.00–117.95 is VOR only
ILS Localizer	108.10–111.95 MHz	Odd tenths only — 108.10, 108.15, 108.30, etc.
ILS Glideslope	329.15–335.00 MHz	Paired automatically with localizer frequency
Outer Marker	75 MHz	400 Hz tone — blue light, continuous dashes
Middle Marker	75 MHz	1300 Hz tone — amber light, alternating dots and dashes
Inner Marker	75 MHz	3000 Hz tone — white light, continuous dots
DME	960–1215 MHz	Paired with VOR/ILS — X and Y channels
TACAN (military)	960–1215 MHz	Military equivalent of DME
NDB / ADF	190–535 kHz	Low frequency — susceptible to static interference
VHF Direction Finding (VDF)	118–136 MHz	Ground-based DF for VHF communication frequencies

System	Frequency	Notes
Transponder interrogation	1030 MHz	Ground radar interrogates aircraft
Transponder reply	1090 MHz	Aircraft replies on 1090 MHz
ADS-B Out	1090 MHz	1090ES is required at and above FL180 (Class A). Below FL180, 1090ES or UAT meets the 14 CFR 91.225 rule in Class B/C and above 10,000 ft MSL
UAT (ADS-B Out and In)	978 MHz	US-only; ADS-B Out below FL180, plus FIS-B weather and TIS-B traffic uplinks
TCAS interrogation	1030 MHz	Traffic alert and collision avoidance
TCAS reply	1090 MHz
Mode S selective interrogation	1030 MHz	Interrogates specific aircraft by 24-bit ICAO address

Frequencies vary by airport. Check the Chart Supplement (formerly AFD) or approach plates for local frequencies.

Service	Frequency	Description
ATIS	Discrete VHF — check approach plate	Automatic Terminal Information Service — pre-recorded, updated hourly or as needed
D-ATIS	VHF + ACARS datalink	Digital ATIS — same info as voice, available on ACARS
ASOS	Local frequency — see Chart Supplement	Automated Surface Observing System — continuous automated weather
AWOS-1	Local frequency	Wind, temperature/dew point, altimeter, density altitude
AWOS-2	Local frequency	AWOS-1 + visibility
AWOS-3	Local frequency	Full weather — wind, visibility, sky condition, temp/dew point, altimeter
AWOS-3P	Local frequency	AWOS-3 + precipitation type
AWOS-3PT	Local frequency	AWOS-3P + thunderstorm sensor
HIWAS	VOR audio (where available)	Hazardous Inflight Weather Advisory Service — being phased out

Military UHF (225–400 MHz) uses 25 kHz spacing. Specific frequencies vary by installation and classification.

Frequency	Use	Notes
121.500 MHz	Guard / Emergency (VHF)	Monitored by all military aircraft
243.000 MHz	Guard / Emergency (UHF)	Military UHF guard — equivalent to 121.5 MHz
225.000–399.975 MHz	Military UHF air-to-air and ATC	25 kHz channel spacing
282.800 MHz	US Military common	Common military discrete frequency
255.400 MHz	Flight Service (UHF)	FSS UHF frequency used by military aircraft
40.500 MHz	Army VHF-FM guard	Low-band VHF-FM emergency guard (not HF)
8.364 MHz	SAR / Rescue HF	International aeronautical distress HF
3.023 MHz	SAR / On-scene coordination	International aeronautical SAR frequency
5.680 MHz	SAR / On-scene	International aeronautical SAR frequency

Frequency	Use	Notes
121.500 MHz	Emergency / Distress (VHF)	Primary civilian emergency — ELT homing signal
243.000 MHz	Emergency / Distress (UHF)	Military guard — also monitored for SAR
406.028 MHz	COSPAS-SARSAT ELT	Digital distress signal with GPS position — 5W minimum
121.500 MHz	ELT homing	Legacy ELT frequency — used for final homing by SAR aircraft
8.364 MHz	Aeronautical HF distress	International HF distress frequency for aviation
2.182 MHz	Maritime distress (cross-coordination)	Not aviation primary — used for maritime/aviation coordination

Frequency	Use	Notes
75 MHz	Marker beacons (all three)	Outer, middle, and inner markers all use 75 MHz
960–1215 MHz	DME / TACAN	Distance measuring equipment
4200–4400 MHz	Radio altimeter	Terrain clearance measurement below 2,500 ft AGL
5031–5091 MHz	Microwave Landing System (MLS)	Largely unused in the US; UAT and FIS-B are on 978 MHz
9375 MHz	Airborne weather radar	X-band — 3 cm wavelength
13.25–13.40 GHz	Airborne Doppler navigation	Ku-band — Doppler ground speed measurement
14.0–14.5 GHz	Satellite (Ku-band SATCOM)	In-flight WiFi and communications
15.4–15.7 GHz	Aeronautical radionavigation	Ku-band — e.g., some airport surface movement radars