En-Route Flight Advisory Service


  • En-Route Flight Advisory Service (EFAS) provides en-route aircraft with timely and meaningful weather advisories pertinent to the type, route, and altitude of flight
    • EFAS is also a central collection and distribution point for pilot reported weather information (PIREPS)
    • Called En-Route Flight Advisory Service formally but referred to as "flight watch" in the air
    • EFAS is the civilian equivalent of the military Pilot To Metro Service (PMSV)
  • Monitors IR/VR routes
  • Issues airport advisories
  • Handles emergency frequencies
  • Coordinates search and rescue (practice steering available on request) and helps lost aircraft
  • Monitors NAVAIDs
  • Advise customs and immigration of trans-border flights
  • Originate Notice to Airmen (NOTAMs)
  • Since a flight service station may be covering, a large area of land there may be one or more Remote Communications Outlets (RCO), which it monitors through landlines
  • An RCO may be located by itself or with a VHF omni-directional range (VOR)
  • In Alaska, designated FSSs also provide Transcribed Weather Broadcast (TWEB) recordings and take weather observations


  • Low Altitude Services:
    • Range between 5,000' and 17,500' on 122.0 MHz
    • In some regions of the contiguous U.S., especially those that are mountainous, it is necessary to be above 5,000' AGL in order to be at an altitude where the EFAS frequency is available [Figure 1]
      • Other FSS communication frequencies may be available at lower altitudes
    • More open areas may allow for radio reception at lower altitudes than published
  • High Altitude Services:
    • Range between 18,000' to 45,000' MSL on discrete VHF frequencies listed on the front of the high altitude en-route chart and Chart Supplement U.S. [Figure 2 and 3]
    • When coverage permits, these discrete frequencies may be used below 18,000'

En-route Flight Advisory Service Coverage
Figure 1: En-route Flight Advisory Service Coverage
(black indicates mountainous terrain where altitudes above 5,000' AGL are required)
  • Specialists in selected AFSSs controlling multiple Remote Communication Outlets (RCOs) provide coverage of a large geographical area and therefore require your location to respond on the appropriate frequency
    • YOU: "[Facility] Flight Watch, [Callsign], [Location/Nearest VOR]"
      • The specialist needs to know this approximate location to select the most appropriate transmitter/receiver outlet for communications coverage
      • If you do not know which flight watch facility you are reaching, exclude the facility and say "Flight Watch"
      • Its better if you know the station because the operator will better know how to reach back to you on the appropriate frequency
  • Normally, hours of operations are between 6am and 10pm local
    • When an EFAS outlet is located in a time zone different from the zone in which the flight watch control station is located, the availability of service may be plus or minus one hour from the normal operating hours

High Altitude En-route Flight Advisory Service Frequencies
Figure 2: High Altitude En-route Flight Advisory Service Frequencies
  • Reference the Chart Supplement U.S. for the location of flight watch control stations (parent facility) and the outlets they use [Figure 3]
  • EFAS is not intended to be used for filing or closing flight plans, position reporting, getting complete preflight briefings, or obtaining random weather reports and forecasts
    • En route flight advisories are tailored to the phase of flight that begins after climb-out and ends with descent to land
    • Immediate destination weather and terminal aerodrome forecasts will be provided on request
    • Pilots requesting information not within the scope of flight watch will be advised of the appropriate Flight Service Station
      • While an FSS is the same facility as flight watch, you are reaching a different person who can better assist you
  • Pilot participation is essential to the success of EFAS by providing a continuous exchange of information on weather, winds, turbulence, flight visibility, icing, etc., between pilots and flight watch specialists
    • Pilots are encouraged to report good weather as well as bad, and to confirm expected conditions as well as unexpected to EFAS facilities

Pilot-To-Metro Service

  • Pilot to Metro Service (PMSV) is designed to communicate various types of weather information to pilots
    • PMSV is the military equivalent of the En-Route Flight Advisory Service (EFAS)
  • Used to update the Flight Weather Briefing Form (DD-175-1) and receive Pilot Reports (PIREPs)
    • UHF: "[Location] METRO, [Callsign]"
  • Sub-Regional Forecast Center (SRFC):
    • Forecasting has been centralized to support outlying satellite detachments during off-peak hours when a forecaster is not on duty
    • Observers are authorized to provide basic weather information, such as latest field conditions or nearby observations or reading a Terminal Aerodrome Forecast (TAF)
    • The observer acts as an intermediary for anything else, such as any forecast services, DD-175-1 updates or extensions
    • Includes 4 pages for 4 regions (SW/SE/NE/NW)
    • A legend explains what service is available with the symbol located on the map
    • For any site less than continuously manned, there will be an hours of operation page following the maps, as well as a few additional locations that are not charted
    • The map contains the frequency to contact the site
    • A reception chart on the bottom right of the map shows limits
      • You want to be in the white, not the shaded area
Pilot To Metro and Weather Service Information
Figure 3: Pilot To Metro and Weather Service Information


  • All En Route Flight Advisory Service facilities and FSSs have equipment to directly access the radar displays from the individual weather radar sites
    • Specialists at these locations are trained to interpret the display for pilot briefing and inflight advisory services
    • The Center Weather Service Units located in ARTCCs also have access to weather radar displays and provide support to all air traffic facilities within their center’s area
Airport Facility Directory Discrete En-Route Flight Advisory Service Frequencies
Figure 4: Chart Supplement U.S. Discrete Frequencies