Military Transport
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 12
Confusion; Situational Awareness; Workload
ATC Issue All Types; Conflict NMAC; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance
Procedure; Human Factors; Airspace Structure
When Aircraft X checked on with Center they were in the block 240B270 with Aircraft Y. A short time later Aircraft X reported they will break up soon and Aircraft Y is requesting a direct ZZZ at FL400B410 and Aircraft X requested a return at FL260. Controller acknowledged and advised Aircraft X to separate in the block and advised Aircraft Y squawk and frequency. Aircraft Y flight checked on at FL240B250. Aircraft Y requested direct ZZZ and FL340B350 and the controller cleared Aircraft Y direct climb and maintain FL340B350. The controller asked Aircraft X to say altitude. MODE C showed Aircraft X at FL270. Aircraft X responded with a request. The controller then cleared Aircraft X and maintain FL260. Aircraft Y appeared on the radar replay and altitude showed FL258. Aircraft X showed at FL270. The controller radar identified Aircraft Y flight and asked the flight to say altitude. The first reply was broken and then Aircraft Y responded passing 265 for 340 and we had a near collision with Aircraft X. Controller advised MARSA (Military Authority Responsible for Separation) was not terminated. Closest observed separation was .12 miles and 400 feet.I learned from this event that I cannot rely on MARSA. If I am in communication with military aircraft under MARSA and I have not yet terminated MARSA; I will apply all IFR separation rules to the best of my ability; instead of relying on the pilots to separate themselves. Applying that mind set to this particular situation: I would first radar identify Aircraft Y flight. I would clear Aircraft Y flight direct and assign FL240B250. I would then assign Aircraft X direct and assign FL270. Once I had Aircraft Y flight laterally separated from Aircraft X; I would terminate MARSA and climb Aircraft Y flight to the requested altitude. I would then descend Aircraft X to the requested altitude.
Center Controller reported a military aircraft reported a NMAC with another military aircraft as they were exiting their refueling track.