Narrative:

I was working local control east at bos; landing 27 and 22L with lasho; VFR. Strong; gusting winds 26020g44 during the session; at the time of this event it was approximately 26020g40 although I didn't check to verify. A PC12 was the previous arrival and was slow on final; a B737 was next. Both aircraft were cleared to land runway 27. The PC12 landed and was instructed to exit at C taxiway and told about traffic short final. I amended the point of exit to a left on 15R; which is an earlier turn off; but a sharper turn. The PC12 reported that he could make 15R. The PC12 came to about a complete stop to make this turn and was exiting 27 when the asde-X/amass alert went off saying something like 'warning runway 27 occupied' at which time I sent the B737 around. Also; 15R was closed; no taxi between 27 and 22L; that is why I didn't turn the PC12 right on 33L; which would have been an 60 degree turn as opposed to a 120 degree turn. I should have slowed the B737 while he was still 3 miles or so out and/or prepared the PC12 to plan an expedited exit of 27; but I didn't. I thought the PC12 would land and exit in a more timely manner and I thought that the B737 would slow like most of the previous aircraft had. The asde-X/amass alert went off like it is intended; however; I looked out the window and could see that I didn't need to send the B737 because the PC12 was clear of 27. I didn't want to and in my mind didn't need to send the B737 around; but I did in accordance with our rules of following the asde-X/amass alerts. If I were able to override the asde-X/amass; the B737 would have landed. I watched it all the way and was well aware of the situation; but due to the asde-X/amass going off; I had to react to it.

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Original NASA ASRS Text

Title: BOS Controller described a go around event when ASDE-X/AMASS issued an alarm even though visually the reporter confirmed the conflicting traffic was clear of the landing runway.

Narrative: I was working Local Control East at BOS; landing 27 and 22L with LASHO; VFR. Strong; gusting winds 26020G44 during the session; at the time of this event it was approximately 26020G40 although I didn't check to verify. A PC12 was the previous arrival and was slow on final; a B737 was next. Both aircraft were cleared to land Runway 27. The PC12 landed and was instructed to exit at C Taxiway and told about traffic short final. I amended the point of exit to a left on 15R; which is an earlier turn off; but a sharper turn. The PC12 reported that he could make 15R. The PC12 came to about a complete stop to make this turn and was exiting 27 when the ASDE-X/AMASS alert went off saying something like 'Warning Runway 27 Occupied' at which time I sent the B737 around. Also; 15R was closed; no taxi between 27 and 22L; that is why I didn't turn the PC12 right on 33L; which would have been an 60 degree turn as opposed to a 120 degree turn. I should have slowed the B737 while he was still 3 miles or so out and/or prepared the PC12 to plan an expedited exit of 27; but I didn't. I thought the PC12 would land and exit in a more timely manner and I thought that the B737 would slow like most of the previous aircraft had. The ASDE-X/AMASS alert went off like it is intended; however; I looked out the window and could see that I didn't need to send the B737 because the PC12 was clear of 27. I didn't want to and in my mind didn't need to send the B737 around; but I did in accordance with our rules of following the ASDE-X/AMASS alerts. If I were able to override the ASDE-X/AMASS; the B737 would have landed. I watched it all the way and was well aware of the situation; but due to the ASDE-X/AMASS going off; I had to react to it.

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.