Aviation Surface Weather Observation Network (ASWON) is a service portfolio with the following primary and backup weather observation systems that we deploy throughout the National Airspace System (NAS):

• Automated Weather Observing System (AWOS)
• Automated Surface Observing System (ASOS)*
• Automated Weather Sensor System (AWSS)
• Stand Alone Weather Sensors (SAWS)
• Digital Altimeter Setting Indicator (DASI)
• Wind Equipment F-Series (WEF) Wind System

* The National Oceanic and Atmospheric Administration National Weather Service (NWS) maintains ASOS through an interagency agreement.

AWOS, ASOS, and AWSS provide required surface weather observations. These systems generate weather observations containing the following:

• Wind speed, direction, and gust information
• Temperature
• Dew point
• Altimeter setting
• Cloud height and amount
• Visibility
• Present weather
• Precipitation accumulation
• Thunderstorm occurrence

SAWS, WEF F-420 wind system, and DASI provide a second source of required weather parameters at towered/staffed airports in the NAS.

Description of ASWON Portfolio

The ASWON portfolio includes several surface sensors that measure weather parameters on the surface and report conditions to air traffic facilities and pilots. The data collected is not only important to pilots and dispatchers as they prepare and file flight plans but also is vital for weather forecasting.

AWOS, AWSS, and ASOS, which are the primary automated surface observing systems, provide around-the-clock weather observations at airports throughout the NAS. These primary systems construct weather observations using a suite of meteorological sensors typically located at an airfield. The weather observation is broadcast to pilots in the airport vicinity using a Very High Frequency (VHF) radio transmitter or an Automatic Terminal Information Service and provided by dial-up telephone service.

Leased telecommunications services send the Meteorological Terminal Aviation Routine Weather Report's weather observation to users through the national weather data network. NWS uses the observation data to prepare forecast and warning products. Each primary system consists of a sensor group located on the airfield, a platform for data collection (usually collocated with the sensor group), and a centralized data processor which receives data from the data collection platform and processes it using weather algorithms.

As secondary systems, SAWS, DASI, and WEF wind systems are used for backup or enhancement of the primary system weather elements (for example, barometric pressure, wind, and temperature/dew point) and for operational support of air traffic control. SAWS supports primary systems by providing data on wind speed and direction, gust, dew point, and relative humidity. DASI measures the atmospheric pressure and provides data in a digital format at Tower and Terminal Radar Approach Control controller positions. Controllers send the altimeter setting value to aircraft pilots for their use in local settings of the aircraft altimeter. WEF F-400 Series (F-420) wind system provides the required secondary source of wind speed and direction for the air traffic control tower.

ASWON Tech Refresh (TR)

The ASWON TR program will provide technology upgrades or replacements (based on form, fit, or function) to five legacy ASWON systems — ASOS, AWOS, AWSS, DASI, and WEF F-420 — experiencing issues with obsolete or unsupportable parts. This tech refresh will enable these systems to continue providing surface weather observations for the NAS. We expect to complete upgrades by the end of 2020.

ASWON TR will transition legacy surface observation systems to a common hardware and software baseline. To accomplish this, we will procure similar hardware across the portfolio and internally develop software.

Current Goals

The ASWON TR will result in the following key outputs and outcomes:

• The issue of AWSS obsolete parts will be addressed by using hardware identical to the AWOS system.
• The AWSS TR will address the National Transportation Safety Board's safety recommendation SR-A-11-049, which recommends that the FAA "Correct the deficiencies with the in-service Automated Weather Sensor System (AWSS) stations, specifically the known problems with present weather sensors and ceilometers to ensure that the AWSS stations provide accurate information as soon as practical."
• The WEF F-420 hardware will be upgraded to Surface Weather System (SWS).
• Issues with obsolete hardware in regards to C&G-manufactured DASI will be resolved with replacement or installation of DME-manufactured DASI hardware.
• AWOS, AWSS, and ASOS will run an FAA-developed software baseline, resulting in a common platform for all primary surface observation systems and the simplified ability to carry out future requirements. After the TR, the upgraded systems, AWOS-Model C, will be referred to as AWOS-C.
• Current growth of sensor models, Ultra high frequency (UHF)/VHF radio types, main processor types, and software baselines will be eliminated across the ASWON portfolio.

SWS and AWOS-C Tech Refresh (TR) Locations

Currently, 227 SWS and 206 AWOS-C systems are included in the ASWON TR portfolio.