Narrative:

Working light traffic. Had just taken over the sector. Aircraft X was southwest-bound at 8;500 headed to nyc area. I observed a 1200 target moving in the same direction approximately 7 miles south of aircraft X's position. As they were headed in the same direction; no potential conflict appeared to exist; and I took no action. I then observed the 1200 target make a sharp right turn; placing the target in conflict with aircraft X. I issued the traffic to aircraft X as 'just turned northwest; 8;500 feet about 10 seconds later; I determined the two targets were on a collision course and said 'traffic alert; aircraft X climb 500 feet immediately.' I chose a climb because I would expect the other aircraft to dive if he saw aircraft X; and a turn would not be sufficient given proximity to separate the targets. I observed aircraft X comply with the instruction; and reported the aircraft in sight as I observed aircraft X at 8;700. I observed the 1200 code aircraft at 8;600; and the targets merged with aircraft X indicating 8;900. Aircraft X reported the other aircraft to be a lancair.this happened because the 1200 code aircraft did not see aircraft X. Fortunately; I saw the conflict in time to take action to separate the aircraft. This was a very close call.we need to reach out to local pilot groups and encourage them to get flight following. If I had been talking to the 1200 code aircraft; I could have taken action much sooner to prevent these aircraft from getting so close to each other.

Google
 

Original NASA ASRS Text

Title: Boston Center Controller reported a Near Mid Air Conflict between a VFR aircraft under Center's control and a VFR aircraft not under ATC control.

Narrative: Working light traffic. Had just taken over the sector. Aircraft X was southwest-bound at 8;500 headed to NYC area. I observed a 1200 target moving in the same direction approximately 7 miles south of Aircraft X's position. As they were headed in the same direction; no potential conflict appeared to exist; and I took no action. I then observed the 1200 target make a sharp right turn; placing the target in conflict with Aircraft X. I issued the traffic to Aircraft X as 'just turned northwest; 8;500 feet about 10 seconds later; I determined the two targets were on a collision course and said 'Traffic Alert; Aircraft X climb 500 feet immediately.' I chose a climb because I would expect the other aircraft to dive if he saw Aircraft X; and a turn would not be sufficient given proximity to separate the targets. I observed Aircraft X comply with the instruction; and reported the aircraft in sight as I observed Aircraft X at 8;700. I observed the 1200 code aircraft at 8;600; and the targets merged with Aircraft X indicating 8;900. Aircraft X reported the other aircraft to be a Lancair.This happened because the 1200 code aircraft did not see Aircraft X. Fortunately; I saw the conflict in time to take action to separate the aircraft. This was a very close call.We need to reach out to local pilot groups and encourage them to get flight following. If I had been talking to the 1200 code aircraft; I could have taken action much sooner to prevent these aircraft from getting so close to each other.

Data retrieved from NASA's ASRS site 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.