Narrative:

Aircraft X departed an air force base requesting FL310. Aircraft X checked on my frequency and was cleared to climb to FL230. When observed leaving FL180; aircraft X was handed-off and switched to the next sector. Aircraft X was leveled at FL230 for a couple of minutes and checked on my frequency declaring an emergency. The other sector's d-side called me to ask whether or not aircraft X was on my frequency because they were unable to communicate with the pilot. I advised them that the aircraft had returned to my frequency with an emergency. When aircraft X checked on the frequency; he declared an emergency and reported descending. The supervisor on duty was called and notified about the emergency. About 20 miles behind the emergency aircraft was aircraft Y climbing to FL230 and about 15 miles behind that aircraft was a flight of two climbing to the block FL200-FL220. I requested and was given a d-side to coordinate the emergency information. Aircraft X was asked nature of emergency (responding with hydraulics problem; 2 souls on board; fuel remaining) and if requesting assistance on the ground (no assistance needed on the ground). Aircraft Y was stopped at FL210 for the emergency aircraft's decent and turned 30 degrees right for the emergency traffic. The emergency aircraft; aircraft X; was then cleared to descend to 16;000FT direct the air force base then turned to a 170 heading for the traffic. Aircraft X continued his descent and conflict alert was depicted between aircraft X (emergency aircraft) and aircraft Y at approximately FL210. All of the coordination was accomplished and aircraft X was handed-off and shortly switched to approach. Aircraft X took the frequency change. Approach called and notified us that aircraft X was not on their frequency but aircraft X was observed continuing his descent. I then proceeded to try to contact aircraft X but I received no reply. After a few attempts approach notified us that aircraft X was on their frequency. A few minutes later; approach advised us that the emergency aircraft (aircraft X) had landed safely. After further review; I was notified that there was a proximity error (pe) of 4.83 miles between the emergency aircraft (aircraft X) and the departure aircraft (aircraft Y). Recommendation; when receiving an aircraft that is declaring an emergency and descending; I would advise the pilot to maintain an altitude for traffic; and if unable to maintain; I would issue traffic to ensure knowledge of traffic and move the possible traffic away from the emergency traffic without issuing the emergency traffic a specific altitude to maintain.

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Original NASA ASRS Text

Title: Enroute Controller described a loss of separation event while handling several maneuvering military aircraft; noting several actions he/she would initiate in future similar type events.

Narrative: Aircraft X departed an Air Force Base requesting FL310. Aircraft X checked on my frequency and was cleared to climb to FL230. When observed leaving FL180; Aircraft X was handed-off and switched to the next Sector. Aircraft X was leveled at FL230 for a couple of minutes and checked on my frequency declaring an emergency. The other Sector's D-Side called me to ask whether or not Aircraft X was on my frequency because they were unable to communicate with the pilot. I advised them that the aircraft had returned to my frequency with an emergency. When Aircraft X checked on the frequency; he declared an emergency and reported descending. The Supervisor on duty was called and notified about the emergency. About 20 miles behind the emergency aircraft was Aircraft Y climbing to FL230 and about 15 miles behind that aircraft was a flight of two climbing to the block FL200-FL220. I requested and was given a D-Side to coordinate the emergency information. Aircraft X was asked nature of emergency (responding with Hydraulics problem; 2 souls on board; fuel remaining) and if requesting assistance on the ground (no assistance needed on the ground). Aircraft Y was stopped at FL210 for the emergency aircraft's decent and turned 30 degrees right for the emergency traffic. The emergency aircraft; Aircraft X; was then cleared to descend to 16;000FT direct the Air Force Base then turned to a 170 heading for the traffic. Aircraft X continued his descent and conflict alert was depicted between Aircraft X (emergency aircraft) and Aircraft Y at approximately FL210. All of the coordination was accomplished and Aircraft X was handed-off and shortly switched to Approach. Aircraft X took the frequency change. Approach called and notified us that Aircraft X was not on their frequency but Aircraft X was observed continuing his descent. I then proceeded to try to contact Aircraft X but I received no reply. After a few attempts Approach notified us that Aircraft X was on their frequency. A few minutes later; Approach advised us that the emergency aircraft (Aircraft X) had landed safely. After further review; I was notified that there was a Proximity Error (PE) of 4.83 miles between the emergency aircraft (Aircraft X) and the departure aircraft (Aircraft Y). Recommendation; when receiving an aircraft that is declaring an emergency and descending; I would advise the pilot to maintain an altitude for traffic; and if unable to maintain; I would issue traffic to ensure knowledge of traffic and move the possible traffic away from the emergency traffic without issuing the emergency traffic a specific altitude to maintain.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.