In an article posted on The Aviationist website by David Cenciotti, he is reporting that the U.S. Air Force’s gigantic Global Hawk drones have been flying over Ukraine for about two years. However, they recently let everyone know they were there.
Aircraft serial number #04-2021 turned on its ADS-B transponder on October 15 using hex address AE27A7 while flying over Ukraine at 50175 feet squawking 5527.
U.S. RQ-4Bs belonging to the 9th Operations Group/Detachment 4th of the U.S. Air Force deployed to Sigonella from Beale Air Force Base, California, have been flying ISR (Intelligence Surveillance Reconnaissance) missions in support of EUCOM, AFRICOM and CENTCOM theater mission tasking since 2011.
You can read David's entire article at https://theaviationist.com/2016/10/18/u-s-air-force-rq-4-global-hawk-drone-flew-over-ukraine-with-transponder-turned-on-for-everyone-to-see/