Air Force Lt. Col. Jason Halvorsen, a pilot with the District of Columbia Air National Guard's Aerospace Control Alert Detachment, goes through a pre-flight check in an F-16 Fighting Falcon aircraft during a training event at Joint Base Andrews, Maryland, Dec. 19, 2018.  Halvorsen is one of several pilots with the detachment, which is tasked with keeping the Washington, D.C., area safe from airborne threats. The ACAD has responded to more than 6,200 alert events since its formation in the aftermath of the 9/11 attacks. (U.S. Air Force photo by Tech. Sgt. Erich B. Smith)