![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)](https://thenational-the-national-prod.cdn.arcpublishing.com/resizer/v2/B6AKE3KLP54ULGXYDB5TCS7MJE.jpg?smart=true&auth=a464d1d7d3b5a0ebb8340b90145740fa5839d12b8df6f5a5ac56c824c3c70feb&width=400&height=225)
Delta Airlines sent warning notices to pilots about possible furloughs. AP
Delta Airlines sent warning notices to pilots about possible furloughs. AP
Delta could furlough 2,500 pilots as coronavirus hits travel demand
The airline is also exploring a voluntary early retirement option for pilots