WASHINGTON (Reuters) - A U.S. Federal Aviation Administration system that provides safety messages to pilots experienced an outage for several hours on Saturday before resuming operations, the agency and airlines said. The outage of the "Notice to Airmen" system for more than three hours on Saturday was due to a hardware issue. In early February, the system known as NOTAM also suffered a failure. The FAA said the main NOTAM system "experienced a temporary outage and the system was reset." The agency said it was "investigating the root cause ... closely monitoring the situation." The NOTAM system provides pilots, flight crews and other users of U.S. airspace with critical safety notices. It could include items such as taxiway lights being out at an airport, nearby parachute activity or a specific runway being closed for construction. "All active NOTAMs were available until the time of the outage," the FAA said. On Friday, U.S. Transportation Secretary Sean Duffy said he would announce a plan next week to drastically overhaul the aging U.S. air traffic control system. A NOTAM outage in January 2023 disrupted more than 11,000 flights in the first nationwide U.S. ground stop since 2001. A ground stop is an air traffic management initiative in which no aircraft meeting certain criteria can take off. The FAA said in 2023 it planned to discontinue an older NOTAM system by mid-2025. National Air Traffic Controllers Association President Nick Daniels told Congress this month the NOTAM system has led to significant disruptions. "At minimum, the FAA will need $154 million just to conduct further research on a replacement NOTAM system, but will need $354 million to replace the broken NOTAM system," Daniels said. The Government Accountability Office has said the FAA must take urgent action to address aging air traffic control systems, saying that one-third are unsustainable.