Photograph — Gordon Leggett, CC BY-SA 4.0, via Wikimedia Commons
For pilots flying small aircraft at airports devoid of control towers and Flight Service, an Automated Weather Observing System (AWOS) is the sole in-depth local weather picture they receive - but it is not as broad and flexible as the widely known Automatic Surface Observing System (ASOS).
An AWOS is a computerized system installed on the field that automatically measures weather parameters, analyzes the data, and prepares a weather observation specific to that airport, according to official Federal Aviation Administration (FAA) guidance. Pilots can receive that local, current picture by tuning to the AWOS's integral VHF radio signal, an existing navigational aid, or an airport weather information service.
The AWOS creates its airport-specific weather picture every 20 minutes, broadcasting continuously on its VHF frequency, and is also usually available by dialing a telephone access number. Drivers also use telephone access.
The AWOS observation a pilot hears over the air is built from reported data on wind speed and direction, visibility, weather phenomena such as haze or rain in various combinations, and more. A typical AWOS-3PT station broadcasts weather data on its assigned frequency. A typical AWOS broadcast includes data such as:
ALTIMETER
AUTO
***
NO TRANSCRIBER
TEMP 04
DEW POINT -08
-WINDS 250 AT 12 GUSTS 12
WEATHER -SN
SEA LEVEL PRESSURE 30.00
RANGE 5 [
*
Much the way ATIS helps major airports move landed traffic more efficiently, AWOS helps small airports like Floody 68 move flying traffic more efficiently by supplying the local specifics that matter to pilots. The AWOS setup simulates a stripped-down version of ASOS for smaller fields with no local office staffing.
FAA AC 150/5220-16 confirms that ASOS is the broader-identifying term, while AWOS encompasses a smaller subset of systems without some ASOS components. "ASOS provides continuous minute-by-minute observations and basic observing functions necessary to generate an aviation routine weather report (METAR)," the FAA advice states. The Advisory Circular also outlines the cooperative between the FAA, the National Weather Service, and the Department of Defense that runs the AWOS system. An AWOS system meets FAA standards.
But the civilian end of this cooperation is more limited in AWOS than in ASOS. When available by telephone, pilots dialing an AWOS number can hear the same report available on the VHF frequency, but it is up to the airport owner to maintain the system. "Non-Federal AWOS systems are owned and maintained by the airport," the FAA stated in its Joint Order 7900.5E on Surface Weather Observing, released in January 2022. The recorded voice message provides a voice indication of the AWOS equipment operational status.
Pilots using an AWOS observation must be aware of its limits to avoid over-reliance. These sensors have standardized configurations. For example, Some AWOS sites broadcast weather data on their assigned frequencies.
No matter which of those dozens of several types are installed, the data elements are the same, and pilots should interpret the AWOS broadcast as an integration of local data points collected every 20 minutes at best. There may be other weather moving through the area that AWOS will not observe and report, and pilots should remain aware of regional forecasts and weather predictions regardless of what AWOS reports at a given moment.
