UAV - Unpiloted Aerial Vehicle
Air Traffic Control Fully Certified
Communication Breakdown; Confusion
ATC Issue All Types; Conflict Airborne Conflict
Air Traffic Control Issued Advisory / Alert
Human Factors; Procedure
I climbed a flight of 2 Hawks to 150 southbound and handed the flight off to [another sector]. An aircraft was southwest bound at 135/VFR. I performed an automated pointout of this aircraft to [the other sector controller] and handed the flight off. After attempting to hand off the aircraft to [the other sector]; I performed other duties while my D-side attempted to establish communication. I shipped the aircraft and after he left my frequency; the flight of Hawks squawked 1200 and descended just in front of the aircraft. We informed [the next controller] of the flight of Hawks descending in front of the aircraft; so that a traffic alert could be provided. My mains/standby frequency was released and I was on a back-up frequency. This may have attributed to me not being able to hear the flight of Hawks read back the frequency change or the multiple attempts to cancel IFR.
Departure Controller reported an airborne conflict between a manned aircraft and a flight of two UAVs.