ASR-9 is an airport surveillance radar system admitted into the National Airspace System (NAS), to be utilized by the Federal Aviation Administration to monitor civilian and commercial air traffic within the United States. Developed by Westinghouse, ASR-9 was the first radar system to display air traffic, and weather conditions simultaneously. The ASR-9 is mainly intended to monitor and track aircraft below 25,000 ft and within forty to sixty nautical miles from the airport of operation. The ASR radar systems were widely used where an advanced radar system was needed, consisting of 135 different ASR-9 operating locations around the U.S. The FAA is currently working to upgrade the remaining ASR-9 radar sites to a modernized digital version known as the ASR-11.