Narrative:

I was working one spot for a rotation when a d-side only got me out to go finish my rotation at another position; I was next on the list to get up when the next controller was to return in less than 5 minutes. I do not understand the management side of the equation; but I do not like getting someone out; working for 5 minutes; and then another controller sitting down at the same sector to get me out. The multiple transfers of controllers are not safe in my opinion. I sat down at the new position and got a briefing. The controller informed me of all the pertinent data and told me about the two aircraft both at FL320 converging head on that were at this time about five minutes or more from the conflict point. It was slow and not complex. The prior controller told me he was going to descend the lander to FL300 and it would be an easy fix; to which I agreed. I sat down; switched a few aircraft; checked a couple on; and made a couple transmissions because I had plenty of time to fix the problem. I think it is a disservice to the aircraft to descend them too many miles earlier then needed. This is something that I will not be concerned with in the future after the situation that took place. Then I had about 3 minutes until the conflict and I tried to descend the lander. No answer. I tried him a few times; no answer. I put a pvd on the adjacent sector and called them with the intention to have them see if they were still talking to the aircraft. At this point I still thought it was a non-issue. The adjacent sector did not answer. I called 3 or 4 times; no answer. At this point I tried to descend the other aircraft; no answer; tried again; no answer. The aircraft were two minutes from the conflict point and they were both NORDO. Now I have a serious problem. I knew at this point I had 2 minutes to get a hold of one of the aircraft or they were going to hit. I shouted at the adjacent sector on the shout line and yelled if you are talking to 'call sign' descend him to FL300 immediately. I yelled for a d-side to assist me; and already; the next controller was back on his way over to get me out. He sat on my d-side. The two planes start to flash. I call the other sector that was working the other aircraft; and I yelled; 'break for control'; meanwhile the adjacent controller yells on the shout line that the aircraft was coming over descending to FL300. The landing aircraft checked in descending to FL300. They were 1 to 1.5 minutes from hitting. Problem averted. This is the worst situation I have ever witnessed in my career. When I work a sector I highlight all aircraft; and when they check in I take the highlight off so I know at all times who I am; and who I am not talking to. I assumed that I was talking to both aircraft when I took over the sector but I was not; controller contribution to the situation. The one landing aircraft was never on the frequency and he was at least 5-10 minutes in my sector when I sat down. I believe the other aircraft was not listening or accidentally turned their radio off or something. When I asked the controller who relieved me; he said that the aircraft just came on asking for higher; but I think it was his way of finding out if he was on the right frequency. I may be incorrect with this assumption; but it is my opinion. Pilot error may play a part in this situation. My other problem with this situation is the fact that I had to call the adjacent sector several times without an answer.

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Original NASA ASRS Text

Title: Enroute Controller described a developing conflict event when assuming two conflicting aircraft were on his frequency but were not; the reporter noting this event was the worst situation ever experienced.

Narrative: I was working one spot for a rotation when a D-Side only got me out to go finish my rotation at another position; I was next on the list to get up when the next Controller was to return in less than 5 minutes. I do not understand the management side of the equation; but I do not like getting someone out; working for 5 minutes; and then another Controller sitting down at the same sector to get me out. The multiple transfers of controllers are not safe in my opinion. I sat down at the new position and got a briefing. The Controller informed me of all the pertinent data and told me about the two aircraft both at FL320 converging head on that were at this time about five minutes or more from the conflict point. It was slow and not complex. The prior Controller told me he was going to descend the lander to FL300 and it would be an easy fix; to which I agreed. I sat down; switched a few aircraft; checked a couple on; and made a couple transmissions because I had plenty of time to fix the problem. I think it is a disservice to the aircraft to descend them too many miles earlier then needed. This is something that I will not be concerned with in the future after the situation that took place. Then I had about 3 minutes until the conflict and I tried to descend the lander. NO ANSWER. I tried him a few times; no answer. I put a PVD on the adjacent sector and called them with the intention to have them see if they were still talking to the aircraft. At this point I still thought it was a non-issue. The adjacent sector did not answer. I called 3 or 4 times; no answer. At this point I tried to descend the other aircraft; NO ANSWER; tried again; no answer. The aircraft were two minutes from the conflict point and they were BOTH NORDO. NOW I HAVE A SERIOUS PROBLEM. I knew at this point I had 2 minutes to get a hold of one of the aircraft or they were going to hit. I shouted at the adjacent sector on the shout line and yelled if you are talking to 'Call sign' descend him to FL300 immediately. I yelled for a D-Side to assist me; and already; the next Controller was back on his way over to get me out. He sat on my D-Side. The two planes start to flash. I call the other sector that was working the other aircraft; and I yelled; 'BREAK FOR CONTROL'; meanwhile the adjacent Controller yells on the shout line that the aircraft was coming over descending to FL300. The landing aircraft checked in descending to FL300. They were 1 to 1.5 minutes from hitting. Problem averted. This is the worst situation I have ever witnessed in my career. When I work a sector I highlight all aircraft; and when they check in I take the highlight off so I know at all times who I am; and who I am not talking to. I assumed that I was talking to both aircraft when I took over the sector but I was not; Controller contribution to the situation. The one landing aircraft was never on the frequency and he was at least 5-10 minutes in my sector when I sat down. I believe the other aircraft was not listening or accidentally turned their radio off or something. When I asked the Controller who relieved me; he said that the aircraft just came on asking for higher; but I think it was his way of finding out if he was on the right frequency. I may be incorrect with this assumption; but it is my opinion. Pilot error may play a part in this situation. My other problem with this situation is the fact that I had to call the adjacent sector several times without an answer.

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.