Russian air defense systems may have brought down an Azerbaijani airliner, shown here, in Kazakhstan this week, a U.S. official said Friday. (The Administration of Mangystau Region via AP)

This art designed by Boeing shows one concept for the Air Force's future fighter, known as Next Generation Air Dominance. (Boeing)

The military is resuming flights of its tiltrotor V-22 Ospreys after ordering inspections of a gearbox to see which might be at risk of metal failure. (Mass Communication Specialist 3rd Class Amber Smalley/U.S. Navy)

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Spc. Zachary Scarpetti of the 10th Mountain Division performs drone operator qualifications near Mihail Kogalniceanu Airbase, Romania. (Sgt Kourtney Nunnery/Army)