Narrative:

I was controller in charge. Sfo was busy and the ceilings were low. Tbm (time based metering) was not in use. Traffic volume was high because the weather moved in earlier than expected. Also contributing to the traffic volume and complexity was the strong surface winds at the airport; approximately 30 KTS or more. This caused compression to be high. Air carrier X was following a heavy aircraft. Both were cleared for the ILS28R. I was watching the entire area as controller in charge. I became aware of the situation when the finals controller said that he had a 'close one' and he asked me to check it on the prm monitor. I went to the prm monitor and saw that the spacing tool had already been activated by someone and the mileage was 5.25; 5 miles was required. The spacing looked adequate and I said so. The final controller issued a frequency change to sfo tower. The tower sent air carrier X around. I reported the go around to the operations manager who subsequently measures the spacing as 4.97. I am not sure if 5 miles was lost while they were on approach or during the go-around. 1) if the finals controller is unsure as to whether he has separation; he should take immediate action to ensure separation. Asking for a second opinion from the controller in charge or flm causes valuable time to be wasted. 2) controllers in our area have made a habit of checking the prm scope to determine if they have adequate spacing. This means controllers are often leaving their sectors (cord-stretching) to check their spacing. Perhaps we should staff the prm scope during in-trail non-tbm operations. This would add a second set of eyes to ensure separation. I believe this is currently done in some facilities such as atl. The benefits of creating such a procedure would be [that] the position responsibilities would be clear and controllers would not have to cord stretch to use the prm scope. Although I used the prm scope during this possible error; I did it as controller in charge. I didn't monitor the frequency and I knew nothing of the assigned speeds. This put me in the position of having to make a snap judgment without having all the facts. 3) lastly; I want to express my frustration with having an error that is 3/100ths of a mile short of the required separation. There needs to be some kind of leeway; such as proximity event; for errors of this kind. Three hundredths of a mile is 180 ft. I don't believe safety was compromised. To put it another way; we had 99.994% of the required separation.

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Original NASA ASRS Text

Title: NCT CIC described a loss of separation behind a heavy jet; noting the difficulty of controllers trying to discern 100ths of a mile distinctions when working with the current equipment.

Narrative: I was CIC. SFO was busy and the ceilings were low. TBM (Time Based Metering) was not in use. Traffic volume was high because the weather moved in earlier than expected. Also contributing to the traffic volume and complexity was the strong surface winds at the airport; approximately 30 KTS or more. This caused compression to be high. Air Carrier X was following a heavy aircraft. Both were cleared for the ILS28R. I was watching the entire area as CIC. I became aware of the situation when the Finals Controller said that he had a 'close one' and he asked me to check it on the PRM monitor. I went to the PRM monitor and saw that the spacing tool had already been activated by someone and the mileage was 5.25; 5 miles was required. The spacing looked adequate and I said so. The Final Controller issued a frequency change to SFO Tower. The Tower sent Air Carrier X around. I reported the go around to the Operations Manager who subsequently measures the spacing as 4.97. I am not sure if 5 miles was lost while they were on approach or during the go-around. 1) If the Finals Controller is unsure as to whether he has separation; he should take immediate action to ensure separation. Asking for a second opinion from the CIC or FLM causes valuable time to be wasted. 2) Controllers in our area have made a habit of checking the PRM scope to determine if they have adequate spacing. This means controllers are often leaving their sectors (cord-stretching) to check their spacing. Perhaps we should staff the PRM scope during in-trail non-TBM operations. This would add a second set of eyes to ensure separation. I believe this is currently done in some facilities such as ATL. The benefits of creating such a procedure would be [that] the position responsibilities would be clear and controllers would not have to cord stretch to use the PRM scope. Although I used the PRM scope during this possible error; I did it as CIC. I didn't monitor the frequency and I knew nothing of the assigned speeds. This put me in the position of having to make a snap judgment without having all the facts. 3) Lastly; I want to express my frustration with having an error that is 3/100ths of a mile short of the required separation. There needs to be some kind of leeway; such as proximity event; for errors of this kind. Three hundredths of a mile is 180 FT. I don't believe safety was compromised. To put it another way; we had 99.994% of the required separation.

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.