Narrative:

As we were getting vectored for an approach to runway 14R at bfi (ATIS broadcast VMC conditions and was advertising ILS to 14R); we were expecting a visual approach. When ATC cleared us for the visual approach; they specified the harbor visual approach procedure without a proper heads-up. We quickly reviewed and briefed the harbor visual approach while trying to descend as the clearance happened while we were still at a high altitude. As we were trying to descend; we received a TA due to a VFR crossing our path on final; which further prevented an effective descent (ATC also pointed out the traffic). We were between 800 to 1200 feet and outside of the stabilized approach parameters and decided to go around. We advised tower that we were going around. We anticipated receiving instructions from the tower controller and he stated to fly the published missed approach procedure. Knowing that the harbor visual approach did not have a published missed approach procedure we assumed he was referring to the ILS 14R missed approach procedure. While the pilot monitoring (pm) was switching the ipad to the ILS14R procedure; tower pointed out a boeing 777 in close proximity; on approach to seatac airport; which we had in sight. The runways at seatac airport are a magnetic heading of 160 and at bfi; runways are a heading of 140. Our paths were converging over the top of bfi airport. To avoid the boeing 777 and its wake turbulence we kept our altitude at 1500 feet and slightly shifted course to the right to avoid passing directly under the boeing 777's flight path. His altitude appeared to be 400 to 500 feet above us and descending off to our left; (the boeing 777's altitude would have been 1;900 feet over the top of bfi assuming he was on the glide slope). At about this time the pm confirmed the missed approach procedure was to level off at 1500 feet and fly along the localizer course. At this time; the boeing 777 appeared to be descending through our altitude; and we were in imminent danger of the aircraft's wake turbulence. The best course of action was to alter course slightly to the right. At the same time the tower controller stressed that we cannot turn towards seatac airport and needed to fly the publish missed approach procedure (which was now slightly to our left). By the time the radio transmission was completed we were now able to safely return to the ILS 14R missed approach procedure course knowing that the 777 was passing through our altitude. It was about this time that we felt some of the wake turbulence of the boeing 777 that we were trying to avoid. The tower controller handed us over to approach control and the he gave us headings and vectors back to a non-eventful approach/landing to 14R. After landing; tower gave us a phone number to seatac approach control for discussion. Upon calling the seatac approach control; the discussion focused on how we were cleared for a visual approach and then asked to fly a published missed approach for an approach we were not cleared for.suggestions: we were wondering if we had flown the missed approach for the ILS (even though we were cleared for a visual approach); we believe that we still would have been too close (loss of separation) with the boeing 777. The missed approach climb is to 1;500 feet; which is where we were. The crossing traffic was only 400 feet above (1;900 ft.) and descending for sea.

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Original NASA ASRS Text

Title: Global Express (BD70) flight crew reported difficulty complying with ATC clearance during a go-around at BFI because of a traffic conflict and wake turbulence considerations.

Narrative: As we were getting vectored for an approach to runway 14R at BFI (ATIS broadcast VMC conditions and was advertising ILS to 14R); we were expecting a visual approach. When ATC cleared us for the visual approach; they specified the Harbor Visual approach procedure without a proper heads-up. We quickly reviewed and briefed the Harbor Visual approach while trying to descend as the clearance happened while we were still at a high altitude. As we were trying to descend; we received a TA due to a VFR crossing our path on final; which further prevented an effective descent (ATC also pointed out the traffic). We were between 800 to 1200 feet and outside of the stabilized approach parameters and decided to go around. We advised tower that we were going around. We anticipated receiving instructions from the Tower Controller and he stated to fly the published missed approach procedure. Knowing that the Harbor Visual approach did not have a published missed approach procedure we assumed he was referring to the ILS 14R missed approach procedure. While the Pilot Monitoring (PM) was switching the iPad to the ILS14R procedure; Tower pointed out a Boeing 777 in close proximity; on approach to SeaTac Airport; which we had in sight. The runways at SeaTac Airport are a magnetic heading of 160 and at BFI; runways are a heading of 140. Our paths were converging over the top of BFI airport. To avoid the Boeing 777 and its wake turbulence we kept our altitude at 1500 feet and slightly shifted course to the right to avoid passing directly under the Boeing 777's flight path. His altitude appeared to be 400 to 500 feet above us and descending off to our left; (the Boeing 777's altitude would have been 1;900 feet over the top of BFI assuming he was on the glide slope). At about this time the PM confirmed the missed approach procedure was to level off at 1500 feet and fly along the localizer course. At this time; the Boeing 777 appeared to be descending through our altitude; and we were in imminent danger of the aircraft's wake turbulence. The best course of action was to alter course slightly to the right. At the same time the Tower Controller stressed that we cannot turn towards SeaTac Airport and needed to fly the publish missed approach procedure (which was now slightly to our left). By the time the radio transmission was completed we were now able to safely return to the ILS 14R missed approach procedure course knowing that the 777 was passing through our altitude. It was about this time that we felt some of the wake turbulence of the Boeing 777 that we were trying to avoid. The Tower Controller handed us over to Approach Control and the he gave us headings and vectors back to a non-eventful approach/landing to 14R. After landing; Tower gave us a phone number to SeaTac approach control for discussion. Upon calling the SeaTac Approach Control; the discussion focused on how we were cleared for a visual approach and then asked to fly a published missed approach for an approach we were not cleared for.Suggestions: We were wondering if we had flown the missed approach for the ILS (even though we were cleared for a visual approach); we believe that we still would have been too close (loss of separation) with the Boeing 777. The missed approach climb is to 1;500 feet; which is where we were. The crossing traffic was only 400 feet above (1;900 ft.) and descending for SEA.

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.