a. Weather service to aviation is a joint effort of the National Weather Service (NWS), the Federal Aviation Administration (FAA), the military weather services, and other aviation oriented groups and individuals. The NWS maintains an extensive surface, upper air, and radar weather observing program; a nationwide aviation weather forecasting service; and provides limited pilot briefing service (interpretational). The majority of pilot weather briefings are provided by FAA personnel at Flight Service Stations (AFSS's/FSS's). Aviation routine weather reports (METAR) are taken manually by NWS, FAA, contractors, or supplemental observers. METAR reports are also provided by Automated Weather Observing System (AWOS) and Automated Surface Observing System (ASOS).

REFERENCE-
AIM, Weather Observing Programs, Paragraph 7-1-11.

b. Aerodrome forecasts are prepared by approximately 100 Weather Forecast Offices (WFO's). These offices prepare and distribute approximately 525 aerodrome forecasts 4 times daily for specific airports in the 50 States, Puerto Rico, the Caribbean and Pacific Islands. These forecasts are valid for 24 hours and amended as required. WFO's prepare over 300 route forecasts and 39 synopses for Transcribed Weather Broadcasts (TWEB), and briefing purposes. The route forecasts are issued 3 times daily, each forecast is valid for 15 hours. A centralized aviation forecast program originating from the Aviation Weather Center (AWC) in Kansas City was implemented in October 1995. In the conterminous U.S., all Inflight Advisories Significant Meteorological Information (SIGMET's), Convective SIGMET's, and Airmen's Meteorological Information (AIRMET's) and all Area Forecasts (FA's) (6 areas) are now issued by AWC. FA's are prepared 3 times a day in the conterminous U.S. and Alaska (4 times in Hawaii), and amended as required. Inflight Advisories are issued only when conditions warrant. Winds aloft forecasts are provided for 176 locations in the 48 contiguous States and 21 locations in Alaska for flight planning purposes. (Winds aloft forecasts for Hawaii are prepared locally.) All the aviation weather forecasts are given wide distribution through the Weather Message Switching Center Replacement (WMSCR) in Atlanta, Georgia, and Salt Lake City, Utah.

REFERENCE-
AIM, Inflight Weather Advisories, Paragraph 7-1-5.

c. Weather element values may be expressed by using different measurement systems depending on several factors, such as whether the weather products will be used by the general public, aviation interests, international services, or a combination of these users. FIG 7-1-1 provides conversion tables for the most used weather elements that will be encountered by pilots.

7-1-2. FAA Weather Services

a. The FAA maintains a nationwide network of Automated Flight Service Stations (AFSS's/FSS's) to serve the weather needs of pilots. In addition, NWS meteorologists are assigned to most ARTCC's as part of the Center Weather Service Unit (CWSU). They provide Center Weather Advisories (CWA's) and gather weather information to support the needs of the FAA and other users of the system.

b. The primary source of preflight weather briefings is an individual briefing obtained from a briefer at the AFSS/FSS. These briefings, which are tailored to your specific flight, are available 24 hours a day through the use of the toll free number (1-800-WX BRIEF). Numbers for these services can be found in the Airport/Facility Directory (A/FD) under "FAA and NWS Telephone Numbers" section. They may also be listed in the U.S. Government section of your local telephone directory under Department of Transportation, Federal Aviation Administration, or Department of Commerce, National Weather Service. NWS pilot weather briefers do not provide aeronautical information (NOTAM's, flow control advisories, etc.) nor do they accept flight plans.

REFERENCE-
AIM, Preflight Briefing, Paragraph 7-1-3, explains the types of preflight briefings available and the information contained in each.
 

FIG 7-1-1
Weather Elements Conversion Tables

 

c. Other sources of weather information are as follows:

1. Telephone Information Briefing Service (TIBS) (AFSS), a small number of Transcribed Weather Broadcast (TWEB) locations, and telephone access to the TWEB (TEL-TWEB) provide continuously updated recorded weather information for short or local flights. Separate paragraphs in this section give additional information regarding these services.

REFERENCE-
AIM, Telephone Information Briefing Service (TIBS), Paragraph 7-1-7.
AIM, Transcribed Weather Broadcast (TWEB), Paragraph 7-1-8.

2. Weather and aeronautical information are also available from numerous private industry sources on an individual or contract pay basis. Information on how to obtain this service should be available from local pilot organizations.

3. The Direct User Access Terminal System (DUATS) can be accessed by pilots with a current medical certificate toll-free in the 48 contiguous States via personal computer. Pilots can receive alpha-numeric preflight weather data and file domestic VFR and IFR flight plans. The following are the contract DUATS vendors:

GTE Federal Systems
15000 Conference Center Drive
Chantilly, VA 22021-3808
Computer Modem Access Number: For filing flight plans and obtaining weather briefings: (800) 767-9989
For customer service: (800) 345-3828

Data Transformation Corporation
108-D Greentree Road
Turnersville, NJ 08012
Computer Modem Access Number: For filing flight plans and obtaining weather briefings: (800) 245-3828
For customer service: (800) 243-3828

d. Inflight weather information is available from any FSS within radio range. The common frequency for all AFSS's is 122.2. Discrete frequencies for individual stations are listed in the A/FD.

1. Information on In-Flight Weather broadcasts.

REFERENCE-
AIM, Inflight Weather Broadcasts, Paragraph 7-1-9.

2. En Route Flight Advisory Service (EFAS) is provided to serve the nonroutine weather needs of pilots in flight.

REFERENCE-
AIM, En Route Flight Advisory Service (EFAS), Paragraph 7-1-4, gives details on this service.

7-1-3. Preflight Briefing

a. Flight Service Stations (AFSS's/FSS's) are the primary source for obtaining preflight briefings and inflight weather information. Flight Service Specialists are qualified and certificated by the NWS as Pilot Weather Briefers. They are not authorized to make original forecasts, but are authorized to translate and interpret available forecasts and reports directly into terms describing the weather conditions which you can expect along your flight route and at your destination. Available aviation weather reports, forecasts and aviation weather charts are displayed at each AFSS/FSS, for pilot use. Pilots should feel free to use these self briefing displays where available, or to ask for a briefing or assistance from the specialist on duty. Three basic types of preflight briefings are available to serve your specific needs. These are: Standard Briefing, Abbreviated Briefing, and Outlook Briefing. You should specify to the briefer the type of briefing you want, along with your appropriate background information. This will enable the briefer to tailor the information to your intended flight. The following paragraphs describe the types of briefings available and the information provided in each briefing.

REFERENCE-
AIM, Preflight Preparation, Paragraph 5-1-1, for items that are required.

b. Standard Briefing. You should request a Standard Briefing any time you are planning a flight and you have not received a previous briefing or have not received preliminary information through mass dissemination media; e.g., TIBS, TWEB, etc. International data may be inaccurate or incomplete. If you are planning a flight outside of U.S. controlled airspace, the briefer will advise you to check data as soon as practical after entering foreign airspace, unless you advise that you have the international cautionary advisory. The briefer will automatically provide the following information in the sequence listed, except as noted, when it is applicable to your proposed flight.

1. Adverse Conditions. Significant meteorological and aeronautical information that might influence the pilot to alter the proposed flight; e.g., hazardous weather conditions, airport closures, air traffic delays, etc.

2. VFR Flight Not Recommended. When VFR flight is proposed and sky conditions or visibilities are present or forecast, surface or aloft, that in the briefer's judgment would make flight under visual flight rules doubtful, the briefer will describe the conditions, affected locations, and use the phrase "VFR flight not recommended." This recommendation is advisory in nature. The final decision as to whether the flight can be conducted safely rests solely with the pilot.

3. Synopsis. A brief statement describing the type, location and movement of weather systems and/or air masses which might affect the proposed flight.

NOTE-
These first 3 elements of a briefing may be combined in any order when the briefer believes it will help to more clearly describe conditions.

4. Current Conditions. Reported weather conditions applicable to the flight will be summarized from all available sources; e.g., METAR's/SPECI's, PIREP's, RAREP's. This element will be omitted if the proposed time of departure is beyond 2 hours, unless the information is specifically requested by the pilot.

5. En Route Forecast. Forecast en route conditions for the proposed route are summarized in logical order; i.e., departure/climbout, en route, and descent. (Heights are MSL, unless the contractions "AGL" or "CIG" are denoted indicating that heights are above ground.)

6. Destination Forecast. The destination forecast for the planned ETA. Any significant changes within 1 hour before and after the planned arrival are included.

7. Winds Aloft. Forecast winds aloft will be provided using degrees of the compass. The briefer will interpolate wind directions and speeds between levels and stations as necessary to provide expected conditions at planned altitudes. (Heights are MSL.) Temperature information will be provided on request.

8. Notices to Airmen (NOTAM's).

(a) Available NOTAM (D) information pertinent to the proposed flight.

(b) NOTAM (L) information pertinent to the departure and/or local area, if available, and pertinent FDC NOTAM's within approximately 400 miles of the FSS providing the briefing. AFSS facilities will provide FDC NOTAM's for the entire route of flight.

NOTE-
NOTAM information may be combined with current conditions when the briefer believes it is logical to do so.

NOTE-
NOTAM (D) information and FDC NOTAM's which have been published in the Notices to Airmen Publication are not included in pilot briefings unless a review of this publication is specifically requested by the pilot. For complete flight information you are urged to review the printed NOTAM's in the Notices to Airmen Publication and the A/FD in addition to obtaining a briefing.

9. ATC Delays. Any known ATC delays and flow control advisories which might affect the proposed flight.

10. Pilots may obtain the following from AFSS/FSS briefers upon request:

(a) Information on Military Training Routes (MTR's) and Military Operations Area (MOA's) activity within the flight plan area and a 100 NM extension around the flight plan area.

NOTE-
Pilots are encouraged to request updated information from en route AFSS's.

(b) A review of the Notices to Airmen Publication for pertinent NOTAM's and Special Notices.

(c) Approximate density altitude data.

(d) Information regarding such items as air traffic services and rules, customs/immigration procedures, ADIZ rules, search and rescue, etc.

(e) LORAN-C NOTAM's, available military NOTAM's, and runway friction measurement value NOTAM's.

(f) GPS RAIM availability for 1 hour before to 1 hour after ETA or a time specified by the pilot.

(g) Other assistance as required.

c. Abbreviated Briefing. Request an Abbreviated Briefing when you need information to supplement mass disseminated data, update a previous briefing, or when you need only one or two specific items. Provide the briefer with appropriate background information, the time you received the previous information, and/or the specific items needed. You should indicate the source of the information already received so that the briefer can limit the briefing to the information that you have not received, and/or appreciable changes in meteorological/aeronautical conditions since your previous briefing. To the extent possible, the briefer will provide the information in the sequence shown for a Standard Briefing. If you request only one or two specific items, the briefer will advise you if adverse conditions are present or forecast. (Adverse conditions contain both meteorological and/or aeronautical information.) Details on these conditions will be provided at your request. International data may be inaccurate or incomplete. If you are planning a flight outside of U.S. controlled airspace, the briefer will advise you to check data as soon as practical after entering foreign airspace, unless you advise that you have the international cautionary advisory.

d. Outlook Briefing. You should request an Outlook Briefing whenever your proposed time of departure is six or more hours from the time of the briefing. The briefer will provide available forecast data applicable to the proposed flight. This type of briefing is provided for planning purposes only. You should obtain a Standard or Abbreviated Briefing prior to departure in order to obtain such items as adverse conditions, current conditions, updated forecasts, winds aloft and NOTAM's, etc.

e. When filing a flight plan only, you will be asked if you require the latest information on adverse conditions pertinent to the route of flight.

f. Inflight Briefing. You are encouraged to obtain your preflight briefing by telephone or in person before departure. In those cases where you need to obtain a preflight briefing or an update to a previous briefing by radio, you should contact the nearest AFSS/FSS to obtain this information. After communications have been established, advise the specialist of the type briefing you require and provide appropriate background information. You will be provided information as specified in the above paragraphs, depending on the type briefing requested. In addition, the specialist will recommend shifting to the Flight Watch frequency when conditions along the intended route indicate that it would be advantageous to do so.

g. Following any briefing, feel free to ask for any information that you or the briefer may have missed or are not understood. This way, the briefer is able to present the information in a logical sequence, and lessens the chance of important items being overlooked.

7-1-4. En Route Flight Advisory Service (EFAS)

a. EFAS is a service specifically designed to provide en route aircraft with timely and meaningful weather advisories pertinent to the type of flight intended, route of flight, and altitude. In conjunction with this service, EFAS is also a central collection and distribution point for pilot reported weather information. EFAS is provided by specially trained specialists in selected AFSS's controlling multiple Remote Communications Outlets covering a large geographical area and is normally available throughout the conterminous U.S. and Puerto Rico from 6 a.m. to 10 p.m. EFAS provides communications capabilities for aircraft flying at 5,000 feet above ground level to 17,500 feet MSL on a common frequency of 122.0 MHz. Discrete EFAS frequencies have been established to ensure communications coverage from 18,000 through 45,000 MSL serving in each specific ARTCC area. These discrete frequencies may be used below 18,000 feet when coverage permits reliable communication.

NOTE-
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.

b. Contact flight watch by using the name of the ARTCC facility identification serving the area of your location, followed by your aircraft identification, and the name of the nearest VOR to your position. The specialist needs to know this approximate location to select the most appropriate transmitter/receiver outlet for communications coverage.

EXAMPLE-
Cleveland Flight Watch, Cessna One Two Three Four Kilo, Mansfield V-O-R, over.

c. Charts depicting the location of the flight watch control stations (parent facility) and the outlets they use are contained in the A/FD. If you do not know in which flight watch area you are flying, initiate contact by using the words "Flight Watch," your aircraft identification, and the name of the nearest VOR. The facility will respond using the name of the flight watch facility.

EXAMPLE-
Flight Watch, Cessna One Two Three Four Kilo, Mansfield V-O-R, over.

d. AFSS's that provide En Route Flight Advisory Service are listed regionally in the A/FD's.

e. 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 AFSS/FSS frequency to obtain the information. 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.

7-1-5. Inflight Weather Advisories

a. The NWS issues inflight weather advisories designated as Severe Weather Forecast Alerts (AWW's), Convective SIGMET's (WST's), SIGMET's (WS's), Center Weather Advisories (CWA's), and AIRMET's (WA's). Inflight advisories serve to notify en route pilots of the possibility of encountering hazardous flying conditions which may not have been forecast at the time of the preflight briefing. Whether or not the condition described is potentially hazardous to a particular flight is for the pilot and/or aircraft dispatcher in a 14 CFR Part 121 operation to evaluate on the basis of experience and the operational limits of the aircraft. Inflight weather advisories in the contiguous U.S. are described and plotted primarily using high altitude VOR's as reference points. In Alaska and Hawaii, advisories are described and plotted using either geographic references or latitude/longitude coordinates.

b. Severe Weather Forecast Alerts (AWW's) are preliminary messages issued in order to alert users that a Severe Weather Bulletin (WW) is being issued. These messages define areas of possible severe thunderstorms or tornado activity. The messages are unscheduled and issued as required by the Aviation Weather Center at Kansas City, Missouri.

1. Each AWW is numbered sequentially beginning January 1 of each year.

EXAMPLE-
MKC AWW 161755
WW 279 SEVERE TSTM NY PA NJ
161830Z-170000Z
AXIS..70 STATUTE MILES EITHER SIDE OF LINE..10W KMSS TO 20E KABE..AVIATION COORDS..60NM EITHER SIDE/60NW KSLK - 35W KEWR..HAIL SURFACE AND ALOFT..2 INCHES. SURFACE WIND GUSTS..65 KNOTS. MAX TOPS TO 540. MEAN WIND VECTOR 19020.
REPLACES WW 278..OH PA NY

2. Status reports are issued as needed on Severe Weather Watch Bulletins to show progress of storms and to delineate areas no longer under the threat of severe storm activity. Cancellation bulletins are issued when it becomes evident that no severe weather will develop or that storms have subsided and are no longer severe.

c. Convective SIGMET's (WST's) in the Conterminous U.S.: WST's concern only thunderstorms and related phenomena (tornadoes, heavy precipitation, hail, and high surface winds) over the conterminous U.S. and imply the associated occurrence of turbulence, icing, and convective low level wind shear. Individual WST's for each day are numbered sequentially (00-1-99), beginning at 00Z. The affected geographic area is contained in the number; i.e., the first WST issued each day in the eastern U.S. is Convective SIGMET 1E, the second is Convective SIGMET 2E, and so forth. WST's are issued on a scheduled basis, hourly at 55 minutes past the hour (H+55), and are valid for two hours or until superseded by the next hourly update. WST's are issued for any of the following phenomena:

1. Severe thunderstorm due to:

(a) Surface winds greater than or equal to 50 knots.

(b) Hail at the surface greater than or equal to ³/₄ inches in diameter.

(c) Tornadoes.

2. Embedded thunderstorms.

3. A line of thunderstorms.

4. Thunderstorms greater than or equal to VIP level 4 affecting 40% or more of an area at least 3,000 square miles.

NOTE-
Since thunderstorms are the reason for issuing the WST, severe or greater turbulence, severe icing, and low-level wind shear (gust fronts, downbursts, microbursts, etc.) are implied and will not be specified in the advisory.

d. Convective SIGMET Bulletins.

1. Three Convective SIGMET bulletins, each covering a specified geographic area, are issued. These areas are the Eastern (E), Central (C), and Western (W) U.S. The boundaries that separate the Eastern from the Central and the Central from the Western U.S. are 87 and 107 degrees West, respectively. These bulletins are issued on a scheduled basis, hourly at 55 minutes past the hour (H+55), and as special bulletins on an unscheduled basis.

2. Each of the Convective SIGMET bulletins will be:

(a) Made up of one or more individually numbered Convective SIGMET's,

(b) Valid for two hours or until superseded by the next hourly issuance.

(c) The text of the bulletin consists of either an observation and a forecast or just a forecast.

3. On an hourly basis, an outlook is made for each of the three Convective SIGMET regions. The outlook for a particular region is appended to the Convective SIGMET bulletin for the same region. The convective outlook is also appended to special Convective SIGMET's. The outlook is reviewed each hour and revised when necessary. The outlook is a forecast and meteorological discussion for thunderstorm systems that are expected to require Convective SIGMET issuances during a time period 2-6 hours into the future. Furthermore, an outlook will always be made for each of the three regions, even if it is a negative statement.

e. SIGMET's (WS's) within the conterminous U.S. are issued by the Aviation Weather Center (AWC) when the following phenomena occur or are expected to occur:

1. Severe or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms.

2. Severe icing not associated with thunderstorms.

3. Duststorms, sandstorms, or volcanic ash lowering surface or inflight visibilities to below three miles.

4. Volcanic eruption.

f. Volcanic eruption SIGMET's are identified by an alphanumeric designator which consists of an alphabetic identifier and issuance number. The first time an advisory is issued for a phenomenon associated with a particular weather system, it will be given the next alphabetic designator in the series and will be numbered as the first for that designator. Subsequent advisories will retain the same alphabetic designator until the phenomenon ends. In the conterminous U.S., this means that a phenomenon that is assigned an alphabetic designator in one area will retain that designator as it moves within the area or into one or more other areas. Issuances for the same phenomenon will be sequentially numbered, using the same alphabetic designator until the phenomenon no longer exists. Alphabetic designators NOVEMBER through YANKEE, except SIERRA and TANGO are only used for SIGMET's, while designators SIERRA, TANGO and ZULU are used for AIRMET's.

g. Center Weather Advisories (CWA's).

1. CWA's are unscheduled inflight, flow control, air traffic, and air crew advisory. By nature of its short lead time, the CWA is not a flight planning product. It is generally a Nowcast for conditions beginning within the next two hours. CWA's will be issued:

(a) As a supplement to an existing SIGMET, Convective SIGMET or AIRMET.

(b) When an Inflight Advisory has not been issued but observed or expected weather conditions meet SIGMET/AIRMET criteria based on current pilot reports and reinforced by other sources of information about existing meteorological conditions.

(c) When observed or developing weather conditions do not meet SIGMET, Convective SIGMET, or AIRMET criteria; e.g., in terms of intensity or area coverage, but current pilot reports or other weather information sources indicate that existing or anticipated meteorological phenomena will adversely affect the safe flow of air traffic within the ARTCC area of responsibility.

2. The following example is a CWA issued from the Kansas City, Missouri, ARTCC. The "3" after ZKC in the first line denotes this CWA has been issued for the third weather phenomena to occur for the day. The "301" in the second line denotes the phenomena number again (3) and the issuance number (01) for this phenomena. The CWA was issued at 2140Z and is valid until 2340Z.

EXAMPLE-
ZKC3 CWA 032140
ZKC CWA 301 VALID UNTIL 032340
ISOLD SVR TSTM over KCOU MOVG SWWD 10 KTS ETC.

h. AIRMET's (WA's) may be of significance to any pilot or aircraft operator and are issued for all domestic airspace. They are of particular concern to operators and pilots of aircraft sensitive to the phenomena described and to pilots without instrument ratings and are issued by the AWC for the following weather phenomena which are potentially hazardous to aircraft:

1. Moderate icing.

2. Moderate turbulence.

3. Sustained winds of 30 knots or more at the surface.

4. Widespread area of ceilings less than 1,000 feet and/or visibility less than three miles.

5. Extensive mountain obscurement.

i. AIRMET's are issued on a scheduled basis every six hours, with unscheduled amendments issued as required. AIRMET's have fixed alphanumeric designator with ZULU for icing and freezing level data, TANGO for turbulence, strong surface winds, and wind shear, and SIERRA for instrument flight rules and mountain obscuration.

7-1-6. Categorical Outlooks

a. Categorical outlook terms, describing general ceiling and visibility conditions for advanced planning purposes are used only in area forecasts and are defined as follows:

1. LIFR (Low IFR). Ceiling less than 500 feet and/or visibility less than 1 mile.

2. IFR. Ceiling 500 to less than 1,000 feet and/or visibility 1 to less than 3 miles.

3. MVFR (Marginal VFR). Ceiling 1,000 to 3,000 feet and/or visibility 3 to 5 miles inclusive.

4. VFR. Ceiling greater than 3,000 feet and visibility greater than 5 miles; includes sky clear.

b. The cause of LIFR, IFR, or MVFR is indicated by either ceiling or visibility restrictions or both. The contraction "CIG" and/or weather and obstruction to vision symbols are used. If winds or gusts of 25 knots or greater are forecast for the outlook period, the word "WIND" is also included for all categories including VFR.

EXAMPLE-
1. LIFR CIG-low IFR due to low ceiling.
2. IFR FG-IFR due to visibility restricted by fog.
3. MVFR CIG HZ FU-marginal VFR due to both ceiling and visibility restricted by haze and smoke.
4. IFR CIG RA WIND-IFR due to both low ceiling and visibility restricted by rain; wind expected to be 25 knots or greater.

7-1-7. Telephone Information Briefing Service (TIBS)

a. TIBS, provided by automated flight service stations (AFSS's) is a continuous recording of meteorological and aeronautical information, available by telephone. Each AFSS provides at least four route and/or area briefings. In addition, airspace procedures and special announcements (if applicable) concerning aviation interests may also be available. Depending on user demand, other items may be provided; i.e., METAR observations, terminal aerodrome forecasts, wind/temperatures aloft forecasts, etc.

b. TIBS is not intended to substitute for specialist-provided preflight briefings. It is, however, recommended for use as a preliminary briefing, and often will be valuable in helping you to make a "go or no go" decision.

c. TIBS is provided by Automated Flight Service Stations (AFSS's) and provides continuous telephone recordings of meteorological and/or aeronautical information. Specifically, TIBS provides area and/or route briefings, airspace procedures, and special announcements (if applicable) concerning aviation interests.

d. Depending on user demand, other items may be provided; i.e., surface observations, terminal forecasts, winds/temperatures aloft forecasts, etc. A TOUCH- TONETM telephone is necessary to fully utilize the TIBS program.

e. Pilots are encouraged to avail themselves of this service. TIBS locations are found at AFSS sites and can be accessed by use of 1-800-WX BRIEF toll free number.

7-1-8. Transcribed Weather Broadcast (TWEB)

Equipment is provided at three AFSS/FSS locations in the lower 48 States (Arcata, California; Kankakee, Illinois; Princeton, Minnesota) and all of Alaska, by which meteorological and aeronautical data are recorded on tapes and broadcast continuously over selected low-frequency (190-535 kHz) navigational aids (L/MF ranges or H facilities) and/or VOR's. Broadcasts are made from a series of individual tape recordings, and changes, as they occur, are transcribed onto the tapes. The information provided varies depending on the type equipment available. Generally, the broadcast contains route-oriented data with specially prepared NWS forecasts, Inflight Advisories, and winds aloft plus preselected current information, such as weather reports (METAR/SPECI), NOTAM's, and special notices. In some locations, the information is broadcast over the local VOR only and is limited to such items as the hourly weather for the parent station and up to 5 immediately adjacent stations, local NOTAM information, aerodrome forecast (TAF) for the parent station, adverse conditions extracted from Inflight Advisories, and other potentially hazardous conditions. At selected locations, telephone access to the TWEB has been provided (TEL-TWEB). Telephone numbers for this service are found in the FSS and National Weather Service Telephone Numbers section of the A/FD. These broadcasts are made available primarily for preflight and inflight planning, and as such, should not be considered as a substitute for specialist-provided preflight briefings.

7-1-9. Inflight Weather Broadcasts

a. Weather Advisory Broadcasts. ARTCC's broadcast a Severe Weather Forecast Alert (AWW), Convective SIGMET, SIGMET, or CWA alert once on all frequencies, except emergency, when any part of the area described is within 150 miles of the airspace under their jurisdiction. These broadcasts contain SIGMET or CWA (identification) and a brief description of the weather activity and general area affected.

EXAMPLE-
1. Attention all aircraft, SIGMET Delta Three, from Myton to Tuba City to Milford, severe turbulence and severe clear icing below one zero thousand feet. Expected to continue beyond zero three zero zero zulu.
2. Attention all aircraft, convective SIGMET Two Seven Eastern. From the vicinity of Elmira to Phillipsburg. Scattered embedded thunderstorms moving east at one zero knots. A few intense level five cells, maximum tops four five zero.
3. Attention all aircraft, Kansas City Center weather advisory one zero three. Numerous reports of moderate to severe icing from eight to niner thousand feet in a three zero mile radius of St. Louis. Light or negative icing reported from four thousand to one two thousand feet remainder of Kansas City Center area.

NOTE-
Terminal control facilities have the option to limit the AWW, convective SIGMET, SIGMET, or CWA broadcast as follows: local control and approach control positions may opt to broadcast SIGMET or CWA alerts only when any part of the area described is within 50 miles of the airspace under their jurisdiction.

b. Hazardous InFlight Weather Advisory Service (HIWAS). This is a continuous broadcast of inflight weather advisories including summarized AWW, SIGMET's, Convective SIGMET's, CWA's, AIRMET's, and urgent PIREP's. HIWAS has been adopted as a national program and will be implemented throughout the conterminous U.S. as resources permit. In those areas where HIWAS is commissioned, ARTCC, Terminal ATC, and AFSS/FSS facilities have discontinued the broadcast of inflight advisories as described in the preceding paragraph. HIWAS is an additional source of hazardous weather information which makes these data available on a continuous basis. It is not, however, a replacement for preflight or inflight briefings or real-time weather updates from Flight Watch (EFAS). As HIWAS is implemented in individual center areas, the commissioning will be advertised in the Notices to Airmen Publication.

1. Where HIWAS has been implemented, a HIWAS alert will be broadcast on all except emergency frequencies once upon receipt by ARTCC and terminal facilities, which will include an alert announcement, frequency instruction, number, and type of advisory updated; e.g., AWW, SIGMET, Convective SIGMET, or CWA.

EXAMPLE-
Attention all aircraft. Hazardous weather information (SIGMET, Convective SIGMET, AIRMET, Urgent Pilot Weather Report (UUA), or Center Weather Advisory (CWA), Number or Numbers) for (geographical area) available on HIWAS, Flight Watch, or Flight Service frequencies.

2. In HIWAS ARTCC areas, AFSS/FSS's will broadcast a HIWAS update announcement once on all except emergency frequencies upon completion of recording an update to the HIWAS broadcast. Included in the broadcast will be the type of advisory updated; e.g. AWW, SIGMET, Convective SIGMET, CWA, etc.

EXAMPLE-
Attention all aircraft. Hazardous weather information for (geographical area) available from Flight Watch or Flight Service.

3. HIWAS availability is shown on IFR Enroute Low Altitude Charts and VFR Sectional Charts. The symbol depiction is identified in the chart legend.

7-1-10. Flight Information Services Data Link (FISDL)

a. FISDL. Aeronautical weather and operational information may be displayed in the cockpit through the use of FISDL. FISDL systems are comprised of two basic types: broadcast systems and two-way systems. Broadcast system components include a terrestrial or pace-based transmitter, an aircraft receiver, and a cockpit display device. Two-way systems utilize transmitter/receivers at both the terrestrial or space-based site and the aircraft.

1. Broadcast FISDL allows the pilot to passively collect weather and operational data and to call up that data for review at the appropriate time. In addition to text weather products, such as METAR's and TAF's, graphical weather products, such as radar composite/mosaic images may be provided to the cockpit. Two-way FISDL services permit the pilot to make specific weather and operational information requests for cockpit display.

2. FISDL services are available from three types of service providers.

(a) Through vendors operating under a service agreement with the FAA using broadcast data link on VHF aeronautical spectrum (products and services are defined under subparagraph c).

(b) Through vendors operating under customer contract on aeronautical spectrum.

(c) Through vendors operating under customer contract on other than aeronautical spectrum.

3. FISDL is a method of disseminating aeronautical weather and operational data which augments pilot voice communication with Flight Service Stations (FSS's), other Air Traffic Control (ATC) facilities or Airline Operations Control Centers (AOCC's). FISDL does not replace pilot and controller/flight service specialist/aircraft dispatcher voice communication for critical weather or operational information interpretation. FISDL, however, can provide the background information which can abbreviate and greatly improve the usefulness of such communications. As such, FISDL serves to enhance pilot situational awareness and improve safety.

b. Operational Use of FISDL. Regardless of the type of FISDL system being used, either under FAA service agreement or by an independent provider, several factors must be considered when using FISDL.

1. Before using FISDL in flight operations, pilots and other flight crew members should become completely familiar with the operation of the FISDL system to be used, airborne equipment to be used, including system architecture, airborne system components, service volume and other limitations of the particular system, modes of operation and the indications of various system failures. Users should also be familiar with the content and format of the services available from the FISDL provider(s). Sources of information which may provide this guidance include manufacturer's manuals, training programs and reference guides.

2. FISDL does not serve as the sole source of aeronautical weather and operational information. ATC, FSS, and, if applicable, AOCC VHF/HF voice is the basic method of communicating aeronautical weather, special use airspace, NOTAM and other operational information to aircraft in flight. FISDL augments ATC/FSS/AOCC services, and, in some applications, offers the advantage of graphical data. By using FISDL for orientation, the usefulness of any information received from conventional voice sources may be greatly enhanced. FISDL may alert the pilot to specific areas of concern which will more accurately focus requests made to FSS or AOCC for inflight briefings or queries made to ATC.

3. The aeronautical environment is constantly changing; often these changes occur quickly, and without warning. It is important that critical decisions be based on the most timely and appropriate data available. Consequently, when differences exist between FISDL and information obtained by voice communication with ATC, FSS, and/or AOCC (if applicable), pilots are cautioned to use the most recent data from the most authoritative source.

4. FISDL products, such as ground-based radar precipitation maps, are not appropriate for use in tactical severe weather avoidance, such as negotiating a path through a weather hazard area (an area where a pilot cannot reliably divert around hazardous weather, such as a broken line of thunderstorms). FISDL supports strategic weather decision making such as route selection to avoid a weather hazard area in its entirety. The misuse of information beyond it's applicability may place the pilot and his/her aircraft in great jeopardy. In addition, FISDL should never be used in lieu of an individual pre-flight weather and flight planning briefing.

5. FISDL supports better pilot decision making by increasing situational awareness. The best decision making is based on using information from a variety of sources. In addition to FISDL, pilots should take advantage of other weather/NAS status sources, including, but not limited to, Flight Service Stations, Flight Watch, other air traffic control facilities, airline operation control centers, pilot reports, and their own personal observations.

c. FAA FISDL. The FAA's FISDL system provides flight crews of properly equipped aircraft with a cockpit display of certain aeronautical weather and flight operational information. This information is displayed using both text and graphic format. This system is scheduled for initial operational capability (IOC) in the first quarter of calendar year 2000. The system is operated by vendors under a service agreement with the FAA, using broadcast data link on aeronautical spectrum on four 25 KHz spaced frequencies from 136.425 through 136.500 MHz. FISDL is designed to provide coverage throughout the continental U.S. from 5,000 feet AGL to 17,500 feet MSL, except in those areas where this is unfeasible due to mountainous terrain. Aircraft operating near transmitter sites will receive useable FISDL signals at altitudes lower than 5000 feet AGL, including on the surface in some locations, depending on transmitter/aircraft line of sight geometry. Aircraft operating above 17,500 MSL may also receive useable FISDL signals under certain circumstances.

1. FAA FISDL provides, free of charge, the following basic products:

(a) Aviation Routine Weather Reports (METAR's).

(b) Special Aviation Reports (SPECI's).

(c) Terminal Area Forecasts (TAF's), and their amendments.

(d) Significant Meteorological Information (SIGMET's).

(e) Convective SIGMET's.

(f) Airman's Meteorological Information (AIRMET's).

(g) Pilot Reports (both urgent and routine) (PIREP's); and,

(h) Severe Weather Forecast Alerts (AWW's) issued by the FAA or NWS.

2. The format and coding of these products are described in Advisory Circular AC-00-45, Aviation Weather Services, and paragraph 7-1-28, Key to Aviation Routine Weather Report (METAR) and Aerodrome Forecasts (TAF).

3. Additional products, called Value-Added Products, are available from the vendors on a paid subscription basis. Details concerning the content, format, symbology and cost of these products may be obtained from the following vendors:

(a) BENDIX/KING WxSIGHT
Allied Signal, Inc.
One Technology Center
23500 West 105th Street
Olathe, KS 66061
(913) 712-2613
www.bendixking.com

(b) ARNAV Systems, Inc.
16923 Meridian East
P. O. Box 73730
Puyallup, WA 98373
(253) 848-6060
www.arnav.com

d. Non-FAA FISDL Systems. In addition to FAA FISDL, several commercial vendors provide customers with FISDL on both the aeronautical spectrum and other frequencies using a variety of data link protocols. In some cases, the vendors provide only the communications system which carries customer messages, such as the Aircraft Communications Addressing and Reporting System (ACARS) used by many air carrier and other operators.

1. Operators using non-FAA FISDL for inflight weather and operational information should ensure that the products used conform to the FAA/NWS standards. Specifically, aviation weather information should meet the following criteria:

(a) The products should be either FAA/NWS accepted aviation weather reports or products, or based on FAA/NWS accepted aviation weather reports or products. If products are used which do not meet this criteria, they should be so identified. The operator must determine the applicability of such products to flight operations.

(b) In the case of a weather product which is the result of the application of a process which alters the form, function or content of the base FAA/NWS accepted weather product(s), that process, and any limitations to the application of the resultant product should be described in the vendor's user guidance material.

2. An example would be a NEXRAD radar composite/mosaic map, which has been modified by changing the scaling resolution. The methodology of assigning reflectivity values to the resultant image components should be described in the vendor's guidance material to ensure that the user can accurately interpret the displayed data.

3. To ensure airman compliance with Federal Aviation Regulations, National Airspace System (NAS) status products (such as NOTAM's, Special Use Airspace Status, etc.) and other government flight information should include verbatim transmissions of FAA products. If these products are modified, the modification process, and any limitations of the resultant product should be described in the vendor's user guidance.

7-1-11. Weather Observing Programs

a. Manual Observations. With only a few exceptions, these reports are from airport locations staffed by FAA or NWS personnel who manually observe, perform calculations, and enter these observations into the (WMSCR) communication system. The format and coding of these observations are contained in paragraph 7-1-28, Key to Aviation Routine Weather Report (METAR) and Aerodrome Forecasts (TAF).

b. Automated Weather Observing System (AWOS).