There is no evidence of a cyber-attack at this point, but the president has asked for an investigation, she said. The FAA said it was working to restore a system that alerts pilots to hazards and changes to airport facilities and procedures that had stopped processing updated information. "The FAA is still working to fully restore the Notice to Air Missions (NOTAM) system following an outage. While some functions are beginning to come back on line, National Airspace System operations remain limited," the FAA said on Twitter. A total of 32,578 flights were delayed within, into or out of the United States as of 8:07 a.m. ET (1255 GMT), flight tracking website FlightAware showed, without citing reasons. Another 409 within, into or out of the country were also canceled. Shares of U.S. carriers fell in Wednesday‍‍`s premarket trading. Southwest Airlines was down 2.4%, while Delta Air Lines Inc (DAL.N), United Airlines (UAL.O) and American Airlines (AAL.O) were down about 1%.