A key system that provides safety messages to pilots resumed operating on Sunday after an outage that began the previous night, the Federal Aviation Administration said, in the latest difficulty for the U.S. aviation system in the past week. U.S. Transportation Secretary Sean Duffy said on Sunday the FAA's "Notice to Air Mission," or NOTAM, system is old and needs an upgrade. The system went down late on Saturday, prompting the agency to set up a hotline to send notices every 30 minutes with updates to airlines. "We are investigating the root cause of the outage," the FAA said in a statement on Sunday. 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.

