Narrative:

A cessna 300 was receiving en route radar advisories from me; level at 10;500. When aircraft got about 10 NM northwest of fay; the track coasted and then jumped onto another target about 10 miles away. I had two sectors combined; as was working several IFR and VFR aircraft in different parts of those two sectors. I had the pilot ident; but I was having trouble seeing him; due to numerous limited data blocks (ldb) in the area; in fay TRACON airspace; underneath and around him. I noticed a limited data block and called fay to ask what altitude this aircraft was climbing to; since there were VFR parachute operations in the vicinity being conducted. I was afraid the cessna 300 was going to be traffic for the limited data block aircraft. Fay said that he was staying at 060 ft. Since I had other duties to perform; IFR handoffs and coordination; I was splitting my time between that situation and the rest of my duties. Shortly thereafter; the cessna 300 said he saw an aircraft pass 400 ft below him; and sounded very concerned about it. Since I still did not have a full data block associated with the cessna 300; I was having difficulty trying to see what just happened. It was then I realized the cessna 300 was squawking the same beacon code as the VFR parachute aircraft. That is why the data block jumped. I assigned the cessna 300 a new beacon code and re-identified him. I apologized and said that my radar was not tracking correctly; and also that fay TRACON had not told me about that aircraft climbing. Subsequent discussion with fay TRACON revealed that the VFR aircraft with the same code that they were working; had told them he would stay below 10;000. Regardless; I needed a point out from fay so I could tell my aircraft that. They also said that their guy had my guy in sight the whole time. That was little comfort to me or the pilot during all of this. Many times a day; especially weekends; numerous VFR aircraft operate parachute operations at several airports fay controls. These aircraft routinely climb to between 11;000 and 14;500 to initiate the jumps. It happens so fast; that we do not take radar handoffs from fay; rather we accept point outs on the ldb's. In this case; I hadn't received a timely point out on their aircraft; and I did not point out my aircraft to them; even though he was only 500 ft above their upper airspace limit. Had both of us done this; it would have helped; and I might have noticed the fact that both aircraft were on the same squawk.

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Original NASA ASRS Text

Title: ZDC Controller described a conflict event involving a parachute operation aircraft that was on an identical code as another VFR operation causing the data block to 'jump' making the developing conflict difficult to identify.

Narrative: A Cessna 300 was receiving en route RADAR advisories from me; level at 10;500. When aircraft got about 10 NM northwest of FAY; the track coasted and then jumped onto another target about 10 miles away. I had two sectors combined; as was working several IFR and VFR aircraft in different parts of those two sectors. I had the pilot ident; but I was having trouble seeing him; due to numerous limited data blocks (LDB) in the area; in FAY TRACON airspace; underneath and around him. I noticed a limited data block and called FAY to ask what altitude this aircraft was climbing to; since there were VFR parachute operations in the vicinity being conducted. I was afraid the Cessna 300 was going to be traffic for the limited data block aircraft. FAY said that he was staying at 060 FT. Since I had other duties to perform; IFR handoffs and coordination; I was splitting my time between that situation and the rest of my duties. Shortly thereafter; the Cessna 300 said he saw an aircraft pass 400 FT below him; and sounded very concerned about it. Since I still did not have a full data block associated with the Cessna 300; I was having difficulty trying to see what just happened. It was then I realized the Cessna 300 was squawking the same beacon code as the VFR parachute aircraft. That is why the data block jumped. I assigned the Cessna 300 a new beacon code and re-identified him. I apologized and said that my RADAR was not tracking correctly; and also that FAY TRACON had not told me about that aircraft climbing. Subsequent discussion with FAY TRACON revealed that the VFR aircraft with the same code that they were working; had told them he would stay below 10;000. Regardless; I needed a point out from FAY so I could tell my aircraft that. They also said that their guy had my guy in sight the whole time. That was little comfort to me or the pilot during all of this. Many times a day; especially weekends; numerous VFR aircraft operate parachute operations at several airports FAY controls. These aircraft routinely climb to between 11;000 and 14;500 to initiate the jumps. It happens so fast; that we do not take RADAR handoffs from FAY; rather we accept point outs on the LDB's. In this case; I hadn't received a timely point out on their aircraft; and I did not point out my aircraft to them; even though he was only 500 FT above their upper airspace limit. Had both of us done this; it would have helped; and I might have noticed the fact that both aircraft were on the same squawk.

Data retrieved from NASA's ASRS site as of July 2013 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.