Narrative:

Seattle north flow; all the aircraft coming into the airspace on the hawks 4 arrival had to be vectored off the arrival to be sequenced with the other arrival legs. I took radar from ZSE sector 2 on aircraft X and when he checked in; the first thing I said was fly heading 340; reduce speed to 210 and descend to 8000ft. I did not hear it at the time; but the [company] that checked in was aircraft Y descending via the hawks 4 arrival. I did not have the hand-off on aircraft Y nor was he flashing to me from ZSE sector 2. I gave multiple control instructions to aircraft Y thinking it was aircraft X until I questioned the aircraft that the heading I gave him did not appear he was flying. That is when aircraft Y said he was heading 320 descending out of FL240 to 8000. At that time I realized what was happening and told aircraft Y to disregard my control instructions and return to his previous frequency and I called ZSE sector 2 and told them I needed to talk to aircraft X who was joining the localizer at seattle as the hawks 4 instructs them to do. Because aircraft X was not sequenced; final did not have the hand-off on them and had cleared aircraft Z for a visual approach. I told final what was happening and he vectored aircraft Z to the northeast and at that point; aircraft X checked on and I vectored him to the northwest. The loss was right around 2.9 miles instead of the needed 3.this is a similar sounding call sign and an attention to detail with listening to call sign problem. I should have heard the wrong call sign when they checked in and the airline needs to ensure that they don't schedule similar sounding call signs to arrive at the airport at the same time.

Google
 

Original NASA ASRS Text

Title: S46 and ZSE Controllers reported confusion with similar call signs that led to a loss of separation.

Narrative: Seattle North flow; all the aircraft coming into the airspace on the HAWKS 4 Arrival had to be vectored off the arrival to be sequenced with the other arrival legs. I took radar from ZSE Sector 2 on Aircraft X and when he checked in; the first thing I said was fly heading 340; reduce speed to 210 and descend to 8000ft. I did not hear it at the time; but the [company] that checked in was Aircraft Y descending via the HAWKS 4 Arrival. I did not have the hand-off on Aircraft Y nor was he flashing to me from ZSE Sector 2. I gave multiple control instructions to Aircraft Y thinking it was Aircraft X until I questioned the aircraft that the heading I gave him did not appear he was flying. That is when Aircraft Y said he was heading 320 descending out of FL240 to 8000. At that time I realized what was happening and told Aircraft Y to disregard my control instructions and return to his previous frequency and I called ZSE Sector 2 and told them I needed to talk to Aircraft X who was joining the localizer at Seattle as the HAWKS 4 instructs them to do. Because Aircraft X was not sequenced; final did not have the hand-off on them and had cleared Aircraft Z for a visual approach. I told Final what was happening and he vectored Aircraft Z to the northeast and at that point; Aircraft X checked on and I vectored him to the northwest. The loss was right around 2.9 miles instead of the needed 3.This is a similar sounding call sign and an attention to detail with listening to call sign problem. I should have heard the wrong call sign when they checked in and the airline needs to ensure that they don't schedule similar sounding call signs to arrive at the airport at the same time.

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.