Backup Automated Weather Observing System (AWOS) for Airports

Airports are reliant upon their technology. One of the most valuable pieces of technology at an airport’s disposal is their Automated Weather Observing System (AWOS). Having a top-of-the-line AWOS puts and airport in control of their weather data, makes for safer skies and better-informed pilots, and expands their air traffic capabilities and therefore their profits.

Airports have come to rely upon their AWOS systems, but what happens when an AWOS malfunctions or a sensor shuts down unexpectedly leaving pilots in the dark?

Airports with steady air traffic from Parts 121 and 135 have strict requirements from the Federal Aviation Administration (FAA) for instrument approach and weather minimums. If an airport is unable to reliably provide the necessary information, flights may need to be canceled, delayed, or diverted to nearby airports who can provide the weather information required.

To keep flights on time and arriving, an airport needs not only a functioning AWOS system but also a reliable backup to meet Service Standards from the FAA. With a Backup AWOS, weather data can be disseminated by the observer as SPECI reports until the fully automatic system is back online and issuing METARs again.

For an airport to legally sustain local operations, backup information is required for long-line dissemination for terminal forecast (TAF) production and for local, ground-to-air dissemination.


The level of Backup equipment an airport is required to have by the FAA is dependent upon what level of Service Standards an airport qualifies under.


  1. Occurrence of significant weather events such as low visibility, thunderstorms, and freezing precipitation which is then multiplied by the total number of operations happening at the airport.

  2. Distance to the nearest suitable alternate airport with airports that are a greater distance away from an acceptable alternative rating higher.

  3. Critical airport characteristics such as whether the airport has a maned tower or is considered a hub. 


There are four levels of Service Standards. Only airports which have a commissioned ASOS or AWOS qualify for a Service Standard Level.


This level is fully automated with an ASOS or AWOS providing the entire weather observation with no additional information supplemented by a human observer.
Service Level D provides information on wind, visibility, precipitation and obstruction to vision, cloud height and sky cover, temperature and dewpoint, altimeter, and in some cases freezing rain and lightning reporting capability. 

SERVICE LEVEL C CONSISTS OF ALL THE ALL ELEMENTS PROVIDED IN SERVICE LEVEL D—with the addition of a human observer to supplement information to the automated observations provided by the ASOS or AWOS system. Augmented information includes such weather events as: thunderstorms, tornadoes, hail, virga, volcanic ash, and tower visibility.

During periods where the tower is closed and no human observation is included, an airport reverts to Service Level D. Service Level C also requires backup systems in the event of a malfunction or unresponsive system or sensor.

SERVICE LEVEL B INCLUDES ALL THE ELEMENTS OF SERVICE LEVELS C AND D in addition to longline runway visual range (RVR), freezing drizzle versus freezing rain, ice pellets, and remarks for snow depth and snow increasing rapidly, thunderstorm and lightning location, as well as observed significant weather not at the station. 

SERVICE LEVEL A AIRPORTS INCLUDE ALL THE PREVIOUS STANDARDS + 10-minute longline RVR or additional visibility increments of 1/8, 1/16 and 0. When observed, sector visibility, variable sky condition, cloud layers above 12,000 feet and significant cloud types, widespread dust, sand and other obscurations, and volcanic eruptions, are also added to the observation. 


The FAA categorizes Backup weather equipment as limited capability equipment that is used when no other acceptable source of weather information is available.


When a weather sensor or the entire system malfunctions and fails to supply data, Backup information from an FAA approved sensor will need to be filled in. 

Communication failures on the part of the Automatic Weather Observing System or malfunctions in the long-line communications can prevent the transmission of weather data over the long-line networks. 

If a weather sensor is reporting data but showing non-representative data of the present weather conditions, FAA approved backup equipment is required. 

When a weather observer reviewing the weather data provided by the system as a whole or individual sensor has reason to believe the accuracy is questionable, use of the primary equipment should be discontinued and Backup equipment must be used. 

Backup equipment is used for the same functions as primary weather observing systems. Therefore, it is critical that Backup systems meet the same criteria as their primary counterparts in:


However, at no point in time should Backup equipment be used beyond the manufacturer’s specifications or limitations. This means, to provide the highest quality weather information available, an airport needs the highest quality backup equipment possible.


Backup systems must provide weather data for critical aviation weather elements using FAA approved sensor and equipment when the primary equipment fails or goes offline.  

Wind Direction and Speed 
Temperature/Dew Point  
Altimeter Setting
Data Displays

Although reports of sky condition, visibility, and present weather should also be included there are no equipment requirements provided for those measurements and visual methods utilizing manual methods may be used as needed, though an airport may choose to add these sensors to their Backup system if they wish.

Mesotech’s AWOS systems are FAA-Certified and meet all specifications of the Automated Weather Observing Systems (AWOS) for Non-Federal Applications, Advisory Circular 150/5220-16. 

The Mesotech AWOS I system meets and exceeds all requirements for Backup Weather Systems from the FAA and monitors all critical weather elements. Instead of attempting to cobble together a series of standalone weather sensors which will keep your airport compliant, a Mesotech AWOS I system can meet all your needs with one purchase and provide accurate and reliable readings of wind speed and direction, temperature and dew point, and altimeter barometer setting.  

The AWOS I system also comes with an AWOS data processor and operator terminal for disseminating SPECI reports to supplement nonfunctioning or incomplete METARs so that your airport is always compliant with long-line dissemination for terminal forecast (TAF) production and for local, ground-to-air dissemination. The Mesotech AWOS I system is support by Airport Weather Advisor and can always be built to include additional sensors if your airport feels they are necessary to have in support of the primary system. 

Learn how you can improve flight safety at your airport with a Backup AWOS