Narrative:

We were vectored off the glaser arrival for a left base to ILS 16L. Initially ATC slowed us from 250 KIAS to 190; then immediately to 170 and 160; and finally to 150 KIAS. We were then cleared for the ILS 16L and told to maintain 150 KIAS until dglas. We immediately complied with all speed reductions and captured the localizer and glide slope prior to dglas. On initial contact with the tower; we were cleared to land on 16L. We had just completed the before landing checklist; were on the localizer and glide slope and had the autopilot and auto throttles engaged. At 2;100 ft approximately 1 NM north of dglas the tower canceled the approach clearance and directed a go-around to maintain 2;000 ft MSL and fly the localizer.this led to a somewhat unusual and task-intensive go-around in that it was executed prior to the assigned missed approach altitude and a level off/slight descent was required while in an auto throttle/autopilot coupled approach mode with a 750 ft rod. The pilot flying complied using one push of the toga button to exit the approach mode followed immediately by the disengagement of the auto throttles to stop the climb and level the aircraft as the pilot not flying selected missed approach and the ATC-directed altitude of 2;000 ft on the MCP. I (pilot flying) was now hand-flying the aircraft with raw data localizer guidance only and continuing with aircraft reconfiguration and go-around; this made course control difficult and less accurate than flying with localizer captured guidance and may have led to less than optimal course control on my behalf.as soon as we were level at 2;000 ft in a clean configuration and approximately 200 KIAS; we attempted to re-acquire localizer capture and flight director localizer guidance. We were queried by the tower if we were maintaining the localizer and told to maintain 2;000 ft and turn right heading 195 degrees. This instruction was followed quickly by an instruction to climb and maintain 5;000 ft. We complied and were subsequently vectored for an uneventful ILS 16L. After landing we were given a phone number to contact the tower.the ATC supervisor informed the captain that they were going to review the tapes. During a follow-up phone conversation; the tower supervisor said that a 'loss of separation' event had taken place and an investigation would follow and; at the time; no pilot deviation report was planned but possibly could come later. I ask what caused the loss of separation and was told it was the ATC-assigned turn to a heading of 195 degrees that was the cause and to rest assured it was not due to flight crew action.we are trained and have procedures for go-arounds and missed approaches but these do not accurately reflect or work for a go-around required prior to descending through the missed approach altitude. Level off and follow on navigation is more task-intensive; and the aircrew needs to review and have a plan for this situation. We do not train to it nor are we presented with this situation very often. In retrospect; asking for a heading to fly or better yet asking for a missed approach altitude higher than our current altitude would have made this missed approach much less task-intensive and much more compatible with standard missed approach techniques.

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Original NASA ASRS Text

Title: A loss of required separation with an aircraft on the parallel runway required ATC to cancel the B737-700's approach clearance as they approached the FAF for the ILS 16L at SEA clearing them to instead maintain 2;000 MSL and fly the localizer. The flight crew failed to utilize autoflight systems as required to maintain track and a conflict occurred which was corrected by a vector from the Local Controller.

Narrative: We were vectored off the GLASER arrival for a left base to ILS 16L. Initially ATC slowed us from 250 KIAS to 190; then immediately to 170 and 160; and finally to 150 KIAS. We were then cleared for the ILS 16L and told to maintain 150 KIAS until DGLAS. We immediately complied with all speed reductions and captured the localizer and glide slope prior to DGLAS. On initial contact with the Tower; we were cleared to land on 16L. We had just completed the Before Landing Checklist; were on the Localizer and glide slope and had the autopilot and auto throttles engaged. At 2;100 FT approximately 1 NM north of DGLAS the Tower canceled the approach clearance and directed a go-around to maintain 2;000 FT MSL and fly the Localizer.This led to a somewhat unusual and task-intensive go-around in that it was executed prior to the assigned missed approach altitude and a level off/slight descent was required while in an auto throttle/autopilot coupled approach mode with a 750 FT ROD. The pilot flying complied using one push of the TOGA button to exit the Approach mode followed immediately by the disengagement of the auto throttles to stop the climb and level the aircraft as the pilot not flying selected missed approach and the ATC-directed altitude of 2;000 FT on the MCP. I (pilot flying) was now hand-flying the aircraft with raw data Localizer guidance only and continuing with aircraft reconfiguration and go-around; this made course control difficult and less accurate than flying with Localizer captured guidance and may have led to less than optimal course control on my behalf.As soon as we were level at 2;000 FT in a clean configuration and approximately 200 KIAS; we attempted to re-acquire localizer capture and flight director localizer guidance. We were queried by the Tower if we were maintaining the localizer and told to maintain 2;000 FT and turn right heading 195 degrees. This instruction was followed quickly by an instruction to climb and maintain 5;000 FT. We complied and were subsequently vectored for an uneventful ILS 16L. After landing we were given a phone number to contact the Tower.The ATC Supervisor informed the Captain that they were going to review the tapes. During a follow-up phone conversation; the Tower Supervisor said that a 'loss of separation' event had taken place and an investigation would follow and; at the time; no Pilot Deviation report was planned but possibly could come later. I ask what caused the loss of separation and was told it was the ATC-assigned turn to a heading of 195 degrees that was the cause and to rest assured it was not due to flight crew action.We are trained and have procedures for go-arounds and missed approaches but these do not accurately reflect or work for a go-around required prior to descending through the missed approach altitude. Level off and follow on navigation is more task-intensive; and the aircrew needs to review and have a plan for this situation. We do not train to it nor are we presented with this situation very often. In retrospect; asking for a heading to fly or better yet asking for a missed approach altitude higher than our current altitude would have made this missed approach much less task-intensive and much more compatible with standard missed approach techniques.

Data retrieved from NASA's ASRS site as of April 2012 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.