Narrative:

My pre-solo student and I had been in the left traffic pattern for 14L at bfi practicing landings. The student was flying at the time. There was aircraft Y on final for 14R; which had been called out to us as being on a 7 mile final when we were on the downwind earlier. They remained in sight the whole time while we were turning in the pattern. We happened to roll out on the final leg right next to aircraft Y; at around 500 or 600 ft MSL. We intentionally rolled out early so that aircraft Y crew would not be scared by us turning on to final at the last second. We were well east of the 14L centerline as a result. I observed aircraft Y all of a sudden bank sharply to the west away from us and then initiate a go around followed by bfi telling them to fly the published missed with a handoff to seattle approach. At the time; we were still east of the centerline of our runway. After a couple laps in the pattern; I heard and saw aircraft Y come back in to bfi. The ground controller asked the crew for the go around reason and they stated that we were encroaching on their centerline but did not mention an RA. My student and I discussed what happened. We both agreed that we were well east of the centerline away from aircraft Y and that there should not have been a conflict. However; we think that rolling out early and then descending on final at an angle may have been seen by aircraft Y crew as us setting up for a converging course. The student and I discussed what changes we could make in the future as parallel approaches are an everyday occurrence at bfi. We decided to make sure that each of our corners in the pattern were a full 90 degrees ground track instead of cutting the corner. We also discussed the benefits of submitting and reading ASRS reports.

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Original NASA ASRS Text

Title: Instructor of a single piston engine aircraft reported an airborne conflict in the landing pattern at BFI.

Narrative: My pre-solo student and I had been in the left traffic pattern for 14L at BFI practicing landings. The student was flying at the time. There was Aircraft Y on final for 14R; which had been called out to us as being on a 7 mile final when we were on the downwind earlier. They remained in sight the whole time while we were turning in the pattern. We happened to roll out on the final leg right next to Aircraft Y; at around 500 or 600 ft MSL. We intentionally rolled out early so that Aircraft Y crew would not be scared by us turning on to final at the last second. We were well east of the 14L centerline as a result. I observed Aircraft Y all of a sudden bank sharply to the west away from us and then initiate a go around followed by BFI telling them to fly the published missed with a handoff to Seattle Approach. At the time; we were still east of the centerline of our runway. After a couple laps in the pattern; I heard and saw Aircraft Y come back in to BFI. The ground controller asked the crew for the go around reason and they stated that we were encroaching on their centerline but did not mention an RA. My student and I discussed what happened. We both agreed that we were well east of the centerline away from Aircraft Y and that there should not have been a conflict. However; we think that rolling out early and then descending on final at an angle may have been seen by Aircraft Y crew as us setting up for a converging course. The student and I discussed what changes we could make in the future as parallel approaches are an everyday occurrence at BFI. We decided to make sure that each of our corners in the pattern were a full 90 degrees ground track instead of cutting the corner. We also discussed the benefits of submitting and reading ASRS reports.

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.