Date: 201602
Local time of day: 1201-1800
Location: ZJX.ARTCC, FL
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZJX
ATC / advisory: Center ZJX
Second aircraft: Citation V/Ultra/Encore (C560)
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Second reporter function: Enroute
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Clearance

Narrative: While working 86; I descended Aircraft Y to cross WHITL intersection at FL350.  I then flashed the aircraft to Cigar (R08) for a handoff.  This is a routine crossing and handoff to MIA R08 sector.  MIA R08 took the handoff and I switched the aircraft to their frequency.  A few minutes later I noticed Aircraft X flashing at me south of the active warning area and coordinated with R08.  After 3 attempts I finally got the controller on the shout line and asked if he/she wanted to descend Aircraft Y underneath or go across the top of Aircraft X at FL360.  I explained that I coordinated with sector 16 (my low side sector) that they can take Aircraft Y to FL340 or FL330. The R08 controller explained that he/she would go over the top at FL360 and put in an interim altitude of 36;000 ft. A few minutes later I witnessed the two aircraft approaching WHITL and notice that Aircraft Y descending below FL360.  As I realized Aircraft Y was at FL357 I advised Aircraft X to turn 30 degrees to the left; as he started to execute the turn the pilot explained that he was responding to an RA climb.  I rogered him and when he was finished I advised Aircraft X to maintain FL360 and process to PLYER intersection on course.  I was advised by the CIC (Controller in Charge) that MIA called and we printed strips on both aircraft.


Second narrative: While working an [organization] aircraft and a Military Recovery aircraft from W168 I did not hear Aircraft Y (In Jacksonville Centers airspace) check on the frequency. Shortly after; Jacksonville Center Controller called to coordinate Aircraft Y at FL340; FL330 or FL360 for the opposite direction Aircraft X at FL350.I replied FL360 approved. Since I had not heard Aircraft Y check in. I interpreted the coordination that Jacksonville Center would stop Aircraft Y at FL360. I had control of the data block and I entered interim altitude of FL360.Conflict alert was activated and I observed Aircraft Y descending from FL360; I questioned the pilot and climbed him immediately. I issued the traffic and again issued climbing instructions.A; D-side at the sector may have caught Aircraft Y checking in. Jacksonville center controller could have been more specific on his coordination. Aircraft Y should have attempted to check in again on frequency when he was not acknowledged at FL410.


Synopsis: Three Center controllers reported an operational error. A Controller requests altitude from another centers sector controller and gives them a choice of altitudes. Receiving controller picks one of the three altitudes. Transferring controller issues altitude to aircraft. Two aircraft have a los of separation due to the aircraft descending into the level aircraft's airspace.