Narrative:

Cleared inbound to sfo on the sfo 095 degree right. As we continued inbound approach control inquired if we were still on the 095 degree right. I immediately answered yes, however I then noticed we were 1/2 DOT deflection left of course. Due to our proximity to sfo VOR and the closeness of alignment between the 095 degree right and the 28R localizer I can see the reason for concern. After checking my own radio to verify course and frequency I glanced to check what the PF had tuned in. At the time I observed his radios. He had the 095 degree right of sfo tuned and was correcting. The localizer 28R was dialed on his #2 radio and I do not know if at the time approach questioned us if he was flying the localizer or not. It would take the other pilot just an instant to switch radios back while I was confirming my own. After correcting back we were shortly thereafter cleared for the visual approach and proceeded inbound west/O incident. Possible explanation: we were past the point where one would normally receive the visibility approach clearance. We were obviously in line and sequenced and knew that at any moment a visibility approach would be given. However, our clearance was the 095 degree right and, regardless, that is where we should have been. I was watching for traffic and did not notice the course deviation till approach contacted us. Even if I had been watching my VOR closer I probably wouldn't have felt very alarmed by a 1/2 DOT deflection. I feel the sfo arrs normally work very well and this was possibly an instance of a pilot expecting a clearance, knowing what that clearance will be, and slowly, unintentionally drifting over to line up with the runway. All of this, of course, is contrary to training, actual practice and good common sense, but is a normal human reaction. However, we can't fly clrncs we 'know' or 'expect to get any moment. It's unfortunate that the inbound radial and 28R localizer are so close that even a small deviation can cause a problem. But in this case, that is not the problem--we should have been on the 095 degree right and if there was any deviation common sense would say, 'be off course on the other side if you must be off course at all.'

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR TRACK DEVIATION FROM 095 DEGREE RADIAL INTO SFO DUE TO EXPECTATION OF VISUAL APCH CLRNC.

Narrative: CLRED INBND TO SFO ON THE SFO 095 DEG R. AS WE CONTINUED INBND APCH CTL INQUIRED IF WE WERE STILL ON THE 095 DEG R. I IMMEDIATELY ANSWERED YES, HOWEVER I THEN NOTICED WE WERE 1/2 DOT DEFLECTION LEFT OF COURSE. DUE TO OUR PROX TO SFO VOR AND THE CLOSENESS OF ALIGNMENT BTWN THE 095 DEG R AND THE 28R LOC I CAN SEE THE REASON FOR CONCERN. AFTER CHKING MY OWN RADIO TO VERIFY COURSE AND FREQ I GLANCED TO CHK WHAT THE PF HAD TUNED IN. AT THE TIME I OBSERVED HIS RADIOS. HE HAD THE 095 DEG R OF SFO TUNED AND WAS CORRECTING. THE LOC 28R WAS DIALED ON HIS #2 RADIO AND I DO NOT KNOW IF AT THE TIME APCH QUESTIONED US IF HE WAS FLYING THE LOC OR NOT. IT WOULD TAKE THE OTHER PLT JUST AN INSTANT TO SWITCH RADIOS BACK WHILE I WAS CONFIRMING MY OWN. AFTER CORRECTING BACK WE WERE SHORTLY THEREAFTER CLRED FOR THE VISUAL APCH AND PROCEEDED INBND W/O INCIDENT. POSSIBLE EXPLANATION: WE WERE PAST THE POINT WHERE ONE WOULD NORMALLY RECEIVE THE VIS APCH CLRNC. WE WERE OBVIOUSLY IN LINE AND SEQUENCED AND KNEW THAT AT ANY MOMENT A VIS APCH WOULD BE GIVEN. HOWEVER, OUR CLRNC WAS THE 095 DEG R AND, REGARDLESS, THAT IS WHERE WE SHOULD HAVE BEEN. I WAS WATCHING FOR TFC AND DID NOT NOTICE THE COURSE DEV TILL APCH CONTACTED US. EVEN IF I HAD BEEN WATCHING MY VOR CLOSER I PROBABLY WOULDN'T HAVE FELT VERY ALARMED BY A 1/2 DOT DEFLECTION. I FEEL THE SFO ARRS NORMALLY WORK VERY WELL AND THIS WAS POSSIBLY AN INSTANCE OF A PLT EXPECTING A CLRNC, KNOWING WHAT THAT CLRNC WILL BE, AND SLOWLY, UNINTENTIONALLY DRIFTING OVER TO LINE UP WITH THE RWY. ALL OF THIS, OF COURSE, IS CONTRARY TO TRNING, ACTUAL PRACTICE AND GOOD COMMON SENSE, BUT IS A NORMAL HUMAN REACTION. HOWEVER, WE CAN'T FLY CLRNCS WE 'KNOW' OR 'EXPECT TO GET ANY MOMENT. IT'S UNFORTUNATE THAT THE INBND RADIAL AND 28R LOC ARE SO CLOSE THAT EVEN A SMALL DEV CAN CAUSE A PROB. BUT IN THIS CASE, THAT IS NOT THE PROB--WE SHOULD HAVE BEEN ON THE 095 DEG R AND IF THERE WAS ANY DEV COMMON SENSE WOULD SAY, 'BE OFF COURSE ON THE OTHER SIDE IF YOU MUST BE OFF COURSE AT ALL.'

Data retrieved from NASA's ASRS site as of August 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.