Narrative:

I was in control of flight X en route via an RNAV arrival. I issued flight X direct [fix] to cross at 6;000 feet. Approximately 1 minute later; I observed a mode C intruder target that had climbed VFR eastbound to 7;500 feet. I asked flight X to increase the rate of descent due to VFR traffic eastbound at 7;500 feet. Uncomfortable with the descent; I issued flight X twenty degrees left to descend below the target. I called the traffic again to flight X and he reported the aircraft in sight. I asked if the altitude looked correct and flight X responded with yeah and then 'about a thousand feet above.' at that moment I observed the intruder target descending and asked flight X if he saw the same thing to which he responded yes. I asked if he wanted a turn and then just issued a 110 heading to avoid and allow flight X to pull away. I then got lower from approach to issue an altitude of 5;000 feet to which flight X said he was getting an RA and descending. The target continued to descend into flight X and uncomfortable with that; I called approach again for lower and then issued 3;000 feet to flight X. I advised flight X to proceed direct to a fix when he was clear of the traffic.in hindsight; I am not sure what we are authorized to do once an aircraft is responding to an RA while at the same time you are getting lower with another facility. Once I issued 3;000 feet; I was in danger of being below our mia's (minimum IFR altitude) and not having knowledge of approach's minimum vectoring altitudes. It is my opinion; and I believe our guidance; to allow the aircraft to finish the RA before taking any control action. Outside of a complete 360 turn; I was unsure of what to issue once flight X was in the midst of an RA while an aircraft seemingly was descending right at another aircraft.I think there needs to be guidance on how to handle RA's with intruder targets so as not to leave anything to doubt. TCAS is very valuable but it creates doubt in our minds when we have to sit and watch while it handles the situation. Maybe some pilot interaction as to what they expect from us and do they know what our guidance is when we hear 'we're responding to an RA?'

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Original NASA ASRS Text

Title: ZBW Controller vectored an air carrier off an RNAV Arrival away from an unidentified VFR aircraft on a conflicting course until the air carrier pilot responded to an RA.

Narrative: I was in control of Flight X en route via an RNAV arrival. I issued Flight X direct [fix] to cross at 6;000 feet. Approximately 1 minute later; I observed a Mode C intruder target that had climbed VFR eastbound to 7;500 feet. I asked Flight X to increase the rate of descent due to VFR traffic eastbound at 7;500 feet. Uncomfortable with the descent; I issued Flight X twenty degrees left to descend below the target. I called the traffic again to Flight X and he reported the aircraft in sight. I asked if the altitude looked correct and Flight X responded with yeah and then 'about a thousand feet above.' At that moment I observed the intruder target descending and asked Flight X if he saw the same thing to which he responded yes. I asked if he wanted a turn and then just issued a 110 heading to avoid and allow Flight X to pull away. I then got lower from Approach to issue an altitude of 5;000 feet to which Flight X said he was getting an RA and descending. The target continued to descend into Flight X and uncomfortable with that; I called Approach again for lower and then issued 3;000 feet to Flight X. I advised Flight X to proceed direct to a fix when he was clear of the traffic.In hindsight; I am not sure what we are authorized to do once an aircraft is responding to an RA while at the same time you are getting lower with another facility. Once I issued 3;000 feet; I was in danger of being below our MIA's (Minimum IFR Altitude) and not having knowledge of Approach's Minimum Vectoring Altitudes. It is my opinion; and I believe our guidance; to allow the aircraft to finish the RA before taking any control action. Outside of a complete 360 turn; I was unsure of what to issue once Flight X was in the midst of an RA while an aircraft seemingly was descending right at another aircraft.I think there needs to be guidance on how to handle RA's with intruder targets so as not to leave anything to doubt. TCAS is very valuable but it creates doubt in our minds when we have to sit and watch while it handles the situation. Maybe some pilot interaction as to what they expect from us and do they know what our guidance is when we hear 'we're responding to an RA?'

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.