Narrative:

B777 was cleared for takeoff runway 28R with P180 on short final for runway 28L. As P180 crossed runway 28L threshold amass alerted; 'go around! Runway 28 right occupied runway' I knew that the P180 was landing on runway 28L. I looked at the asde and saw the amass alert and the target of the B777 on runway 28R circled as well as the target on runway 28L circled. There was also another flashing circle between the two targets. I sent the P180 around. I saw the P180 go-around on runway 28L abeam the B777 departing runway 28R. I told the P180 to turn left heading 265 to separate him from the B777; which was going straight out. I saw the two targets on the radar and I issued traffic to the B777. He responded: 'we're IMC' I saw that the targets were diverging but they were at about the same altitude. This is not the first time we have had amass alerts from smaller aircraft landing on runway 28L with traffic on runway 28R. Even though I had seen the P180 on final for runway 28L and I saw the B777 departing runway 28R; the circled target between the runways made me think that I had better send the P180 around. At the time of the alert the P180 was already over the runway so I had no time to think about the situation; only time to say; 'go-around'. Since the finals were clear; I didn't realize that the go-around would be going into the clouds west of the airport so quickly and that visual separation would not be possible with the B777 departing. I feel that the amass false alert created a potentially dangerous situation between the P180 and the B777.

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Original NASA ASRS Text

Title: SFO controller described AMASS alert for traffic landing Runway 28L with traffic departing on Runway 28R. Runway 28L traffic issued mandatory go-around even though runway was observed as clear; resulted in a less than legal separation event as the aircraft ascended through an overcast weather layer.

Narrative: B777 was cleared for takeoff Runway 28R with P180 on short final for Runway 28L. As P180 crossed Runway 28L threshold AMASS alerted; 'GO AROUND! RUNWAY 28 RIGHT OCCUPIED RUNWAY' I knew that the P180 was landing on Runway 28L. I looked at the ASDE and saw the AMASS alert and the target of the B777 on Runway 28R circled as well as the target on Runway 28L circled. There was also another flashing circle between the two targets. I sent the P180 around. I saw the P180 go-around on Runway 28L abeam the B777 departing Runway 28R. I told the P180 to turn left heading 265 to separate him from the B777; which was going straight out. I saw the two targets on the radar and I issued traffic to the B777. He responded: 'We're IMC' I saw that the targets were diverging but they were at about the same altitude. This is not the first time we have had AMASS alerts from smaller aircraft landing on Runway 28L with traffic on Runway 28R. Even though I had seen the P180 on final for Runway 28L and I saw the B777 departing Runway 28R; the circled target between the runways made me think that I had better send the P180 around. At the time of the alert the P180 was already over the runway so I had no time to think about the situation; only time to say; 'Go-around'. Since the finals were clear; I didn't realize that the go-around would be going into the clouds west of the airport so quickly and that visual separation would not be possible with the B777 departing. I feel that the AMASS false alert created a potentially dangerous situation between the P180 and the B777.

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.