Narrative:

The flight, air carrier xyz, from las vegas to san francisco was planned with a fuel load to land at sfo at maximum allowable landing weight. The entire sfo bay area had experienced 2 days of dense fog and subsequent airport closures and delays. Shortly after leveloff it became apparent we would land overweight at the fuel burn rate which existed. I deployed partial speed brakes and got a lower cruise altitude. The copilot and I agreed that even after this action we would still need to lower the landing gear early on the approach to ensure the aircraft was below the maximum allowable landing weight at touchdown. This was done at approximately 25 mi from sfo. Approach control gave us a descent to 6000 ft from 10000 ft. A few moments before reaching 6000 ft, we were asked to report the field in sight. We were given clearance for the quiet bridge visual approach by approach. All 3 of us (there was another pilot on the jump seat) agreed that the previously foggy conditions were dissipating rapidly, yet the field was still not in sight. We did see the san mateo bridge but a fog bank was between that and the field. As this was going on I heard the altitude alert sound. I glanced at the altimeter and saw us at 5700 ft and descending. I immediately raised the nose I was hand-flying and applied power and returned to 6000 ft. The unusual confign of gear down early in the approach contributed to the altitude deviation but the fact that I was not concentrating on my basic responsibility to fly the airplane caused the deviation. Had I waited for the copilot to sight the field and then looked, the lengthy time I spent looking outside and the altitude deviation, would not have occurred.

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Original NASA ASRS Text

Title: B737-500 FLC FAILED TO LEVEL AT ASSIGNED ALT WHILE LOOKING FOR ARPT AT SFO, CA.

Narrative: THE FLT, ACR XYZ, FROM LAS VEGAS TO SAN FRANCISCO WAS PLANNED WITH A FUEL LOAD TO LAND AT SFO AT MAX ALLOWABLE LNDG WT. THE ENTIRE SFO BAY AREA HAD EXPERIENCED 2 DAYS OF DENSE FOG AND SUBSEQUENT ARPT CLOSURES AND DELAYS. SHORTLY AFTER LEVELOFF IT BECAME APPARENT WE WOULD LAND OVERWT AT THE FUEL BURN RATE WHICH EXISTED. I DEPLOYED PARTIAL SPD BRAKES AND GOT A LOWER CRUISE ALT. THE COPLT AND I AGREED THAT EVEN AFTER THIS ACTION WE WOULD STILL NEED TO LOWER THE LNDG GEAR EARLY ON THE APCH TO ENSURE THE ACFT WAS BELOW THE MAX ALLOWABLE LNDG WT AT TOUCHDOWN. THIS WAS DONE AT APPROX 25 MI FROM SFO. APCH CTL GAVE US A DSCNT TO 6000 FT FROM 10000 FT. A FEW MOMENTS BEFORE REACHING 6000 FT, WE WERE ASKED TO RPT THE FIELD IN SIGHT. WE WERE GIVEN CLRNC FOR THE QUIET BRIDGE VISUAL APCH BY APCH. ALL 3 OF US (THERE WAS ANOTHER PLT ON THE JUMP SEAT) AGREED THAT THE PREVIOUSLY FOGGY CONDITIONS WERE DISSIPATING RAPIDLY, YET THE FIELD WAS STILL NOT IN SIGHT. WE DID SEE THE SAN MATEO BRIDGE BUT A FOG BANK WAS BTWN THAT AND THE FIELD. AS THIS WAS GOING ON I HEARD THE ALT ALERT SOUND. I GLANCED AT THE ALTIMETER AND SAW US AT 5700 FT AND DSNDING. I IMMEDIATELY RAISED THE NOSE I WAS HAND-FLYING AND APPLIED PWR AND RETURNED TO 6000 FT. THE UNUSUAL CONFIGN OF GEAR DOWN EARLY IN THE APCH CONTRIBUTED TO THE ALTDEV BUT THE FACT THAT I WAS NOT CONCENTRATING ON MY BASIC RESPONSIBILITY TO FLY THE AIRPLANE CAUSED THE DEV. HAD I WAITED FOR THE COPLT TO SIGHT THE FIELD AND THEN LOOKED, THE LENGTHY TIME I SPENT LOOKING OUTSIDE AND THE ALTDEV, WOULD NOT HAVE OCCURRED.

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.