Narrative:

Cleared for FMS bridge visual runway 28R. Captain is flying using VNAV and using flaps and speed brakes to get back on path. Crossed garow at 4000 ft which is normal. He must have selected flight level change because the airplane descended below VNAV path. Just outside of brijj, which we should have crossed at 1800 ft, I noticed we were at approximately 1200 ft visually. I confirmed that we were low by looking at the runways and the bridge. I immediately indicated this to the captain who leveled off manually. The aircraft got a little below speed. Once back on path, the rest of approach was normal. Contributing to problem was the ILS runway 28R was OTS. Also, the captain was very exhausted due to numerous all night flts prior to this flight and is in the middle of some family problems. I was tired also. I learned to stay in VNAV on this type of approach or don't run the altitude setting all the way down and since it's a visual approach, don't forgot to look outside a lot (even in a glass cockpit airplane). Supplemental information from acn 348390: I had set my altitude alert to field elevation instead of each crossing fix. I was hand flying after garow.

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Original NASA ASRS Text

Title: AN ACR LGT CREW RPTS THAT THEY GOT BELOW THE FMS VISUAL APCH PATH AT SFO. ERROR ADMITTED. ARPT PROB ILS OTS.

Narrative: CLRED FOR FMS BRIDGE VISUAL RWY 28R. CAPT IS FLYING USING VNAV AND USING FLAPS AND SPD BRAKES TO GET BACK ON PATH. CROSSED GAROW AT 4000 FT WHICH IS NORMAL. HE MUST HAVE SELECTED FLT LEVEL CHANGE BECAUSE THE AIRPLANE DSNDED BELOW VNAV PATH. JUST OUTSIDE OF BRIJJ, WHICH WE SHOULD HAVE CROSSED AT 1800 FT, I NOTICED WE WERE AT APPROX 1200 FT VISUALLY. I CONFIRMED THAT WE WERE LOW BY LOOKING AT THE RWYS AND THE BRIDGE. I IMMEDIATELY INDICATED THIS TO THE CAPT WHO LEVELED OFF MANUALLY. THE ACFT GOT A LITTLE BELOW SPD. ONCE BACK ON PATH, THE REST OF APCH WAS NORMAL. CONTRIBUTING TO PROB WAS THE ILS RWY 28R WAS OTS. ALSO, THE CAPT WAS VERY EXHAUSTED DUE TO NUMEROUS ALL NIGHT FLTS PRIOR TO THIS FLT AND IS IN THE MIDDLE OF SOME FAMILY PROBS. I WAS TIRED ALSO. I LEARNED TO STAY IN VNAV ON THIS TYPE OF APCH OR DON'T RUN THE ALT SETTING ALL THE WAY DOWN AND SINCE IT'S A VISUAL APCH, DON'T FORGOT TO LOOK OUTSIDE A LOT (EVEN IN A GLASS COCKPIT AIRPLANE). SUPPLEMENTAL INFO FROM ACN 348390: I HAD SET MY ALT ALERT TO FIELD ELEVATION INSTEAD OF EACH XING FIX. I WAS HAND FLYING AFTER GAROW.

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.