A319 FLT CREW QUESTIONS APPLICATION OF VISUAL SIDE-BY-SIDE APCH PROC WHEN UNABLE TO MAINTAIN VISUAL SEPARATION FROM A COMMANDER ACFT OVERSHOOTING BASE TO FINAL ON APCH TO SFO RWYS 28.

Narrative

CLRED THE VISUAL FOR RWY 28L; SFO TOLD US TO MAINTAIN 180 KTS TO THE BRIDGE; ALSO TOLD US TO MAINTAIN VISUAL SEPARATION ON A COMMANDER ACFT WHICH WAS ON A R BASE; JUST INSIDE THE BRIDGE FOR RWY 28R. THE COMMANDER ROLLED OUT ON FINAL 100 FT ABOVE US AND SLIGHTLY BEHIND US; ABOUT 200 FT TO OUR R. I BELIEVE HE WAS ALSO TOLD TO MAINTAIN VISUAL SEPARATION. OUR TCASII GAVE US AN RA TO DSND AS THE COMMANDER ROLLED OUT OVER US. FIRST OF ALL; 2 ACFT CANNOT MAINTAIN VISUAL SEPARATION ON EACH OTHER UNLESS THEY FLY ABREAST (SIDE-BY-SIDE) FROM EACH OTHER. THIS IS IMPRACTICABLE SINCE NO ONE IS LEADING AND WHO WILL REACT TO WHO? IN OTHER WORDS; ONLY 1 ACFT CAN LEAD AND ONE CAN FOLLOW. ALSO; IT IS IMPOSSIBLE TO MAINTAIN VISUAL SEPARATION WHEN YOU ARE ASSIGNED AN AIRSPD TO MAINTAIN. YOU CAN'T HAVE BOTH. SFO NEEDS TO BE TOLD THIS. AGAIN; IT IS VERY POOR PLANNING TO EVER HAVE 2 ACFT SIDE BY SIDE ON ANY APCHS TO RWY 28L/R AT SFO; REGARDLESS OF WX. THIS MY FRIENDS; IS AN ACCIDENT WAITING TO HAPPEN. IF YOU CONTINUE TO OPERATE IN THIS FASHION; YOU WILL HAVE A MIDAIR. JUST LIKE THE ONE WE NARROWLY AVERTED ON THIS INCIDENT.