StratuxFIS-B: free ADS-B weather, explained
FIS-B (Flight Information Service-Broadcast) is the free weather and airspace data the FAA sends out on 978 MHz from its ADS-B ground stations. Any receiver that hears 978 MHz UAT can show it, Stratux included: NEXRAD radar, METARs, TAFs, PIREPs, TFRs, NOTAMs and more.
You don't need ADS-B Out to get it, and you don't sign up for anything. You need a 978 MHz receiver, an app that draws the data, and line of sight to a ground station.
We built this page from the FAA's own tables in the AIM and AC 00-63B, so the numbers below are the FAA's, not ours.
What FIS-B is
The FAA's Ins and Outs page puts it plainly. FIS-B "is not a client-based service, but rather is always broadcast into the airspace on the UAT frequency." Traffic services like TIS-B and ADS-R are built for each equipped aircraft. FIS-B is the same broadcast for everyone in range.
The weather comes from the National Weather Service and the aeronautical products (NOTAMs, TFRs, special use airspace) come from the FAA. Ground stations uplink it on 978 MHz only. It's never sent on 1090 MHz, so a 1090-only receiver shows traffic and no weather.
For how FIS-B fits next to the traffic side of ADS-B, start with our pilot's guide to how ADS-B works.
What it sends, and how fresh each product is
The AIM lists every FIS-B product with two numbers (AIM 4-5-9, TBL 4-5-9):
- Update interval: how often the source makes new data.
- Transmission interval: how often the ground station rebroadcasts it, and the time within which a new or updated product goes out (95% of the time).
The transmission interval is the one that matters in the cockpit. It's the longest you should wait for a product after you come into range.
| Product | Source updates | Rebroadcast every |
|---|---|---|
| NEXRAD, regional | 2 minutes | 2.5 minutes |
| NEXRAD, CONUS | 2 minutes | 15 minutes |
| METAR / SPECI | 1 minute where available, otherwise as available | 5 minutes |
| TAF / amendments | 6 hours (±15 minutes) | 10 minutes |
| AIRMET, SIGMET, convective SIGMET | as available | 5 minutes |
| PIREPs | as available | 10 minutes |
| NOTAMs (D, FDC) and TFRs | as available | 10 minutes |
| Special use airspace status | as available | 10 minutes |
| Winds and temperatures aloft | 12 hours (±15 minutes) | 10 minutes |
| Lightning | 5 minutes | 5 minutes |
| Icing forecast, cloud tops, turbulence | 60, 30 and 1 minute | 15 minutes |
The AIM table also lists D-ATIS, echo tops, ceilings, 1-minute AWOS, G-AIRMETs, center weather advisories and temporary restricted and military areas. FAA AC 00-63B gives different intervals for several rows, CONUS NEXRAD and TAFs among them. The table above follows the AIM.
Which of these you actually see depends on your app. The FAA notes that product support "will vary based on individual ADS-B avionics" (FAA ADS-B In pilot page).
How far ahead FIS-B reaches
Ground stations don't send the whole country's weather. Each station is assigned an altitude tier, and the tier sets how far out its products reach. The FAA calls this the look-ahead range (AC 00-63B, Appendix A, Figure A-3):
| Product | Surface | Low tier | Medium tier | High tier |
|---|---|---|---|---|
| Regional NEXRAD | 150 nm | 150 nm | 200 nm | 250 nm |
| CONUS NEXRAD | not sent | not sent | yes | yes |
| METARs and TAFs | 100 nm | 250 nm | 375 nm | 500 nm, plus all CONUS Class B and C airports |
| AIRMETs and SIGMETs | 100 nm | 250 nm | 375 nm | 500 nm |
| PIREPs and SUA status | not sent | 250 nm | 375 nm | 500 nm |
| NOTAMs and TFRs | 100 nm | 100 nm | 100 nm | 100 nm |
| Winds and temps aloft | 500 nm | 500 nm | 750 nm | 1,000 nm |
Two things fall out of that table:
- Your destination METAR can be missing early in a long flight. High-tier stations in CONUS send every Class B and C airport, plus everything within 500 nm. The AC's own example is a Dulles to Orlando Executive flight. The pilot sees the KMCO METAR first, and the KORL one shows up once the flight gets within range.
- TFRs only reach 100 nm. The AC points out that at 200 knots you're covering more than 3 nm a minute. With a 100 nm look-ahead and a 10-minute rebroadcast, a pop-up TFR may not leave much time to react.
Why FIS-B needs line of sight and altitude
FIS-B "reception is line-of-sight within the service volume of the ground infrastructure" (AIM 4-5-9). Hills, hangars and the curve of the earth all block it. Climb, and you see more stations.
The four tiers cover different heights (AC 00-63B, Figure A-2):
- High: surface to FL240, best from about 9,100 ft AGL up.
- Medium: surface to 14,000 ft AGL, best from about 2,200 ft AGL.
- Low: surface to 3,000 ft AGL, for the terminal area.
- Surface: radios that serve aircraft "in the immediate vicinity of major airports."
So weather on the ramp is likely near a big airport with a surface radio. Elsewhere it's hit or miss, depending on what's between you and a station. Garmin's GTN Xi pilot's guide puts surface coverage at about 36 major US airports (190-02327-03 Rev. G, p. 5-38). That's why our no weather or traffic guide calls no weather on the ground normal.
The required ceiling is FL240. The FAA expects you can still receive it above that, and AC 00-63B says about 90 percent of service volumes have FIS-B coverage at FL400. Winds and temps aloft go up to FL390.
The details of tiers, range and station placement are in ground stations and coverage. The ground station map shows every FAA station, colored by tier.
Why it's free
The FAA describes FIS-B as "a free service available to aircraft who can receive data over 978 MHz (UAT)" (FAA pilot page). There's no subscription, no account and no registration. If a receiver hears 978 MHz, it gets the same broadcast as a panel-mounted box.
Commercial weather services are a different thing. AC 00-63B notes some vendors offer free or for-fee services, sometimes with tier-based subscriptions.
What FIS-B isn't
- Not a full briefing. The AIM says FIS-B "does not replace a preflight weather briefing." AC 00-63B adds that it may not include every product or NOTAM a briefing has.
- Not for picking through storms. The FAA says the data is for planning and "lacks sufficient resolution and updating capability necessary for tactical aerial maneuvering." In extreme cases NEXRAD "can be up to 15 minutes older than the display's age indication."
- Not every NOTAM. NOTAM-D and FDC broadcasts are limited to the past 30 days. TFRs and NOTAMs with end dates aren't purged.
How Stratux receives FIS-B
On current builds, the 978 MHz radio is the red UATradio. It's a dedicated receiver that decodes on its own chip and sends frames to the Pi (see choosing radios). Stratux passes each weather uplink to your EFB as a GDL90 uplink message, and the app decodes it and draws the map. Source: main/gen_gdl90.go in the Stratux code.
We built the Towers map from the FAA's station list, so you can see which stations should be in range. To check that weather is reaching the receiver, open the web interface at 192.168.10.1:
- Status page, UAT Statistics rows. METARS, TAFS, NEXRAD and the rest count weather by type, and Towers counts the ground stations heard. If the weather counts climb in flight, weather is arriving. The UAT message bar also counts traffic, so it doesn't prove weather on its own.
- Weather page. Shows the 10 most recent reports and anything for airports on your watch list. Set the watch list on the Settings page.
- Towers page. Lists each ground station heard in the last minute, with its position, signal strength and message count.
If those pages fill up and your app stays blank, the problem is between Stratux and the app, not the radio.
Outside the US, FIS-B only exists where someone runs UAT stations. In Canada that's the volunteer CIFIB network. See Stratux in Canada and outside the US.
Frequently asked questions
What is FIS-B in aviation?
FIS-B (Flight Information Service-Broadcast) is free weather and aeronautical information that FAA ADS-B ground stations broadcast on 978 MHz. Any UAT receiver in range can display it, with no ADS-B Out needed.
Is FIS-B weather free?
Yes. The FAA calls FIS-B a free service for aircraft that can receive 978 MHz UAT. There's no subscription and no registration.
Does FIS-B work on 1090 MHz?
No. FIS-B is only broadcast on 978 MHz. A receiver that only hears 1090 MHz gets traffic but no FIS-B weather.
How old is FIS-B radar?
Regional NEXRAD is rebroadcast every 2.5 minutes and CONUS NEXRAD every 15 minutes. The FAA warns the radar image can be up to 15 minutes older than the age your display shows.
Next, read how the traffic side works in TIS-B and ADS-R. Want to practice reading what FIS-B sends? Try METAR Rush.