FILE - In this April 1, 2020 file photo, several dozen mothballed Delta Air Lines jets are parked at Kansas City International Airport in Kansas City, Mo. The skies are clearing up a bit for airlines as states ease lockdown measures and travelers slowly return to airport check-in lines. More airlines are restoring flights to their schedules and investors have taken note, driving up shares for the major airlines after a staggering decline.  (AP Photo/Charlie Riedel, File)
Delta Airlines sent warning notices to pilots about possible furloughs. AP  

Delta could furlough 2,500 pilots as coronavirus hits travel demand