An F-16 from the 40th Flight Test Squadron located at Eglin Air Force Base, Fla., receives fuel from a KC-10 Extender from McGuire AFB, N.J., during flutter testing, Aug. 23, 2019. Flutter testing evaluates the vibration characteristics of the airplane at certain speeds to assess the impact on the plane and identify potential structural weaknesses. (U.S. Air Force photo by Tech. Sgt. John Raven)