Narrative:

Amass operational on configured for landing runways 28, departing runway 1. Sfo was landing runways 28, departing runway 1. It was night, no moon, busy side-by-side arrs to runway 28 with very few departures from runways 1. Arrs were making simultaneous quiet bridge and tipp-toe visual approachs. Aircraft X a light twin aircraft (king air or twin cessna or similar) made quiet bridge arrival for runway 28R alongside aircraft Y on tipp-toe for runway 28L. The 2 aircraft were side-by-side for the last 3-4 mi of the approach and were side-by-side over the lights. I scanned the runways 28 visually and on the asde and both runways 28 appeared clear. Just after both aircraft passed the numbers, the amass alerted. I looked at the asde and saw the target for aircraft X (circled) and the target for aircraft Y (circled) but I could not determine the reason for the alert. We are required to send an aircraft around if we get an amass go around alert on it. Since both aircraft X and aircraft Y were alerting, and I could not see any conflicting traffic for either one, I did not know what to do. Then the amass voice said 'warning, go around runway 28R' and the same message displayed on the asde. I immediately told aircraft X to go around. It was so dark I could not see if aircraft X was still flying. He could have already touched down or perhaps he was just in the flare. The pilot answered that he was going around. I could not give him a reason for the go around because I did not really know what it was, except for an amass alert. Aircraft Y landed without incident. The nature of amass is that when an alert is received, action must be taken immediately. False alerts lessen the controller's confidence in the system and thus increase reaction time to the alert. Suggestion: amass refresher training focusing on the basic capabilities of the system and its use as well as a review and briefing of false alerts to the controllers who use it.

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Original NASA ASRS Text

Title: SFO LCL CTLR RECEIVES AN AMASS (ARPT MOVEMENT AREA SAFETY SYS) ALERT, AND ISSUES A GAR TO A TWIN ON SHORT APCH TO RWY 28R WITH A B737 ON SHORT FINAL TO RWY 28L, BEING UNABLE TO DETERMINE THE NATURE OF THE ALERT.

Narrative: AMASS OPERATIONAL ON CONFIGURED FOR LNDG RWYS 28, DEPARTING RWY 1. SFO WAS LNDG RWYS 28, DEPARTING RWY 1. IT WAS NIGHT, NO MOON, BUSY SIDE-BY-SIDE ARRS TO RWY 28 WITH VERY FEW DEPS FROM RWYS 1. ARRS WERE MAKING SIMULTANEOUS QUIET BRIDGE AND TIPP-TOE VISUAL APCHS. ACFT X A LIGHT TWIN ACFT (KING AIR OR TWIN CESSNA OR SIMILAR) MADE QUIET BRIDGE ARR FOR RWY 28R ALONGSIDE ACFT Y ON TIPP-TOE FOR RWY 28L. THE 2 ACFT WERE SIDE-BY-SIDE FOR THE LAST 3-4 MI OF THE APCH AND WERE SIDE-BY-SIDE OVER THE LIGHTS. I SCANNED THE RWYS 28 VISUALLY AND ON THE ASDE AND BOTH RWYS 28 APPEARED CLR. JUST AFTER BOTH ACFT PASSED THE NUMBERS, THE AMASS ALERTED. I LOOKED AT THE ASDE AND SAW THE TARGET FOR ACFT X (CIRCLED) AND THE TARGET FOR ACFT Y (CIRCLED) BUT I COULD NOT DETERMINE THE REASON FOR THE ALERT. WE ARE REQUIRED TO SEND AN ACFT AROUND IF WE GET AN AMASS GAR ALERT ON IT. SINCE BOTH ACFT X AND ACFT Y WERE ALERTING, AND I COULD NOT SEE ANY CONFLICTING TFC FOR EITHER ONE, I DID NOT KNOW WHAT TO DO. THEN THE AMASS VOICE SAID 'WARNING, GAR RWY 28R' AND THE SAME MESSAGE DISPLAYED ON THE ASDE. I IMMEDIATELY TOLD ACFT X TO GO AROUND. IT WAS SO DARK I COULD NOT SEE IF ACFT X WAS STILL FLYING. HE COULD HAVE ALREADY TOUCHED DOWN OR PERHAPS HE WAS JUST IN THE FLARE. THE PLT ANSWERED THAT HE WAS GOING AROUND. I COULD NOT GIVE HIM A REASON FOR THE GAR BECAUSE I DID NOT REALLY KNOW WHAT IT WAS, EXCEPT FOR AN AMASS ALERT. ACFT Y LANDED WITHOUT INCIDENT. THE NATURE OF AMASS IS THAT WHEN AN ALERT IS RECEIVED, ACTION MUST BE TAKEN IMMEDIATELY. FALSE ALERTS LESSEN THE CTLR'S CONFIDENCE IN THE SYS AND THUS INCREASE REACTION TIME TO THE ALERT. SUGGESTION: AMASS REFRESHER TRAINING FOCUSING ON THE BASIC CAPABILITIES OF THE SYS AND ITS USE AS WELL AS A REVIEW AND BRIEFING OF FALSE ALERTS TO THE CTLRS WHO USE IT.

Data retrieved from NASA's ASRS site as of July 2007 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.