Weather can change rapidly between the time you conduct your preflight briefing and the time you arrive at your destination. A thorough preflight weather check is essential, but it is only a snapshot in time. Smart pilots treat weather awareness as an ongoing process throughout the flight, not a one-time task accomplished on the ground. Two of the most important tools available for gathering weather information while airborne are traditional pilot-to-ATC weather services (including the historic Flight Watch frequency) and the modern digital Flight Information Service-Broadcast, or FIS-B, transmitted through the FAA's Automatic Dependent Surveillance-Broadcast (ADS-B) infrastructure.
Understanding both resources — what they provide, how to access them, and their limitations — is a core competency for every private pilot. The FAA tests this knowledge directly, and more importantly, using these resources correctly in real flight situations can mean the difference between a smooth reroute and a dangerous encounter with convective activity or instrument meteorological conditions (IMC).
Traditional In-Flight Weather via ATC
Air Traffic Control facilities have long served as an in-flight weather resource for pilots. Center controllers, approach controllers, and Flight Service Stations (FSS) can relay weather reports, pilot reports (PIREPs), and updates from other aircraft in the same airspace. Even when you are not talking to ATC for traffic separation purposes — for example, while cruising in uncontrolled airspace under VFR — you can still contact an FSS or an En Route Flight Advisory Service (EFAS) outlet for weather updates.
Flight Watch (EFAS) and the 122.0 MHz Frequency
For decades, 122.0 MHz was the dedicated En Route Flight Advisory Service frequency, universally known as Flight Watch. Flight Watch was a specialized FSS service designed specifically to provide en route weather information to pilots already in flight. A pilot could contact Flight Watch simply by calling "Flight Watch" on 122.0 MHz, and a specialist would provide current weather, SIGMET information, PIREPs, and help with rerouting around hazardous weather.
It is important to note for the FAA knowledge test and for real-world operations: the FAA discontinued the dedicated Flight Watch service in 2015. The 122.0 MHz frequency no longer connects to a specialized weather-only service. FSS functions have been consolidated, and pilots can now reach Flight Service on 1-800-WX-BRIEF or through a series of standard FSS frequencies that vary by region. Many FSS outlets are reached via remote communications outlets (RCOs) on frequencies listed in the Chart Supplement (formerly Airport/Facility Directory). Your sectional chart and the Chart Supplement will show the appropriate FSS frequencies for any area of the country. Despite the discontinuation, the FAA knowledge test still references Flight Watch and its history, so understanding the old system and the current changes is important.
PIREPs: Pilot Weather Reports
One of the most valuable real-time weather products shared through ATC and FSS is the PIREP (Pilot Weather Report). When a controller asks you about the ride, or when you volunteer a report, that information gets encoded into a standardized format and passed to meteorologists and other pilots. PIREPs are particularly valuable for reporting actual icing conditions, turbulence intensity and altitude, cloud tops, and visibility. Because PIREPs come from pilots who just flew through a particular area, they represent observed conditions rather than forecast conditions. When you encounter significant weather, filing a PIREP is not just a courtesy — it is a professional responsibility that helps every other pilot in the system.
FIS-B: Digital Weather in the Cockpit
The modern evolution of in-flight weather services is FIS-B — Flight Information Service-Broadcast. FIS-B is a ground-based broadcast service that transmits weather and aeronautical data to aircraft equipped with compatible ADS-B In avionics. Crucially, FIS-B is a receive-only (broadcast) service — the ground stations transmit continuously, and any aircraft with ADS-B In equipment can receive the data without needing to identify itself or make a radio call.
How FIS-B Works
FIS-B data is transmitted over the 978 MHz UAT (Universal Access Transceiver) datalink frequency by FAA ground stations throughout the contiguous United States and some outlying areas. These ground stations are part of the same ADS-B infrastructure used for traffic surveillance. The ground stations broadcast on a regular cycle, and a compatible cockpit display (such as a dedicated ADS-B receiver connected to a tablet running an EFB application, or an integrated avionics suite) decodes the data and presents it graphically or in text form to the pilot.
It is essential to understand that FIS-B is available on 978 MHz UAT only — aircraft that use only the 1090 MHz Extended Squitter (1090ES) ADS-B Out do not receive FIS-B weather products. This is a commonly tested distinction. Many GA pilots operating below 18,000 feet MSL equip with UAT for precisely this reason — UAT provides both ADS-B Out compliance and FIS-B weather reception in one unit.
What FIS-B Provides
The FIS-B product suite is extensive and includes:
- NEXRAD Radar Imagery (METARs and Regional Mosaic) — graphical precipitation data derived from National Weather Service radar
- METARs — current aviation routine weather reports from reporting stations
- TAFs — terminal aerodrome forecasts
- PIREPs — pilot weather reports uploaded to the system
- AIRMETs and SIGMETs — advisories for significant meteorological hazards
- TFRs (Temporary Flight Restrictions) — airspace restriction notices
- NOTAMs — notices to air missions (select categories)
- Winds and Temperatures Aloft — upper-level wind forecasts
Critical Limitation: FIS-B Weather is NOT Real-Time
This is arguably the most important safety concept surrounding FIS-B, and it is heavily tested on the FAA knowledge exam. FIS-B weather data — especially NEXRAD radar imagery — is delayed. By the time radar data is processed, uploaded to ground stations, broadcast, received by your avionics, and displayed on your screen, the imagery can be several minutes old. The FAA and avionics manufacturers note that the displayed NEXRAD data can reflect conditions from approximately 5 to 20 minutes prior, depending on the product and the refresh cycle.
This delay is not merely an inconvenience — it is a genuine safety hazard if misunderstood. Convective cells can move and intensify rapidly. A pilot who navigates toward a gap in radar returns that appears clear on FIS-B may be heading directly into a cell that has grown and moved since the data was captured. The rule is straightforward: never use FIS-B NEXRAD to navigate through or near convective weather. Use it for strategic awareness and broad weather avoidance planning, and always cross-check with visual observation, onboard weather radar (if equipped), lightning detectors, and ATC advisories.
Similarly, FIS-B METARs are only updated when a new METAR is issued (typically once per hour, or special observations when conditions change significantly). The displayed METAR may not reflect conditions that have changed in the past hour.
Why These Resources Matter
Combining traditional ATC-based services with FIS-B creates a layered in-flight weather picture. ATC can provide real-time verbal advisories, pilot reports from aircraft ahead of you, and information about rapidly developing situations. FIS-B gives you a visual, geographic overview of the broader weather pattern. Neither source alone is sufficient, and neither replaces the other. Competent pilots treat in-flight weather awareness as a continuous loop: check FIS-B for the big picture, listen to ATC for real-time input, look out the window for visual confirmation, and be prepared to deviate or divert when any of those inputs suggests a hazard.
Key Numbers and Rules
- 122.0 MHz: Former Flight Watch (EFAS) frequency — discontinued in 2015; no longer a dedicated weather service.
- 978 MHz UAT: The datalink frequency that carries FIS-B weather products.
- FIS-B = receive only: No ADS-B Out is required to receive FIS-B; only ADS-B In (UAT receiver) is needed.
- NEXRAD delay: FIS-B radar imagery can be 5–20 minutes old; never use it to pick a path through convective weather.
- 1090ES vs. UAT: Only UAT (978 MHz) provides FIS-B; 1090ES ADS-B Out alone does not receive weather products.
- PIREPs: Voluntary in most situations but expected when encountering hazardous conditions; transmitted through FSS and ATC.
- Chart Supplement: Lists current FSS frequencies and RCO locations to contact Flight Service en route.
Common Test Traps
- Treating FIS-B NEXRAD as real-time: The FAA knowledge test frequently asks about the age of FIS-B weather data. Remember — it is delayed, and that delay matters most near convective activity.
- Assuming Flight Watch is still active: Many older study materials reference 122.0 MHz and Flight Watch as if they are current. Know that EFAS was discontinued in 2015 and FSS services are now accessed through other frequencies.
- Confusing ADS-B In and ADS-B Out: ADS-B Out is required for airspace compliance. ADS-B In (specifically UAT) is what actually receives FIS-B weather. A 1090ES-only installation provides Out capability but no FIS-B weather.
- Thinking FIS-B replaces preflight weather planning: FIS-B is an en route supplement, not a substitute for a thorough preflight briefing. The FAA expects pilots to obtain a proper briefing before departure.
- Underestimating PIREPs: Test questions occasionally ask what a pilot should do after encountering unexpected icing or severe turbulence. Filing a PIREP is the correct action — it helps other pilots and feeds the FSS weather picture.