Narrative:

Our aircraft was on right downwind for the lax 24 complex. Lax approach called an medium large transport to our attention at our 1 O'clock position on the ILS for runway 24R. I called the medium large transport in sight. The approach controller said 'follow the medium large transport he's descending on the ILS for runway 24R; he's 2700 ft; cleared for the visual approach runway 24L; do not descend below 2500 ft until instructed by the tower. Contact the tower at harbor freeway.' approach control turned us right to 160 degrees at about the time the medium large transport was at our 2 O'clock. I turned right base and descended from 3500 ft to 3000 ft MSL. At this time my first officer asked approach control if they realized we would fly directly over the top of the medium large transport. Approach control stated that was the intention. We were both still east of the OM and our vertical separation was still between 700 ft and 1000 ft. We purposely remained high on base leg before turning final knowing the medium large transport would pass directly under us. We xed the 24R localizer then turned final for runway 24L, rolling out on the south taxiways. My first officer looked down and to his right and said to me that it appears the medium large transport is lined up with the 24L runway. We called the tower at the harbor freeway and the controller asked us if we still had the medium large transport in sight. The first officer told the controller we did not see the medium large transport for the time he was under us. My first officer asked the tower to confirm that the medium large transport is lined up for runway 24R. The pilot of the medium large transport stated he was lined up for runway 24R. We had the medium large transport in sight at all times except when he passed beneath us; we were heading 160 degree, the medium large transport heading was 250 degree. After speaking with the supervisor by phone, ATC's concern revolved around 2 key factors: 'follow' and 'in sight'. Being directed to follow the medium large transport after we were cleared for the 'visual approach' presented conflicting information. WX was obscured sky visibility 4 mi. The medium large transport and our aircraft were not in sight by the tower (and vice-versa) when we xed over the medium large transport therefore the approach controller was obligated to give us a new vector away from a perceived conflict because we informed ATC we had lost sight of the other aircraft on a visual approach. Our question is why we can be cleared for a visual approach to follow an aircraft on an ILS (parallel runway) when that aircraft can't see the runway, and is not following another aircraft. Our 'follow' aircraft was on the ILS. The reason we passed up the medium large transport was our distance and altitude from touchdown. As we turned final we still were about 6 mi from the end of the 24L runway and about 3000 ft MSL. We feel the procedures controling visual apches permitted by following an aircraft on an ILS need to be examined more closely.

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Original NASA ASRS Text

Title: FLC OF LTT CLRED VISUAL TO LAX FOLLOW MLG ON ILS, LOST SIGHT OF MLG AND ARPT.

Narrative: OUR ACFT WAS ON R DOWNWIND FOR THE LAX 24 COMPLEX. LAX APCH CALLED AN MLG TO OUR ATTN AT OUR 1 O'CLOCK POS ON THE ILS FOR RWY 24R. I CALLED THE MLG IN SIGHT. THE APCH CTLR SAID 'FOLLOW THE MLG HE'S DSNDING ON THE ILS FOR RWY 24R; HE'S 2700 FT; CLRED FOR THE VISUAL APCH RWY 24L; DO NOT DSND BELOW 2500 FT UNTIL INSTRUCTED BY THE TWR. CONTACT THE TWR AT HARBOR FREEWAY.' APCH CTL TURNED US R TO 160 DEGS AT ABOUT THE TIME THE MLG WAS AT OUR 2 O'CLOCK. I TURNED R BASE AND DSNDED FROM 3500 FT TO 3000 FT MSL. AT THIS TIME MY FO ASKED APCH CTL IF THEY REALIZED WE WOULD FLY DIRECTLY OVER THE TOP OF THE MLG. APCH CTL STATED THAT WAS THE INTENTION. WE WERE BOTH STILL E OF THE OM AND OUR VERT SEPARATION WAS STILL BTWN 700 FT AND 1000 FT. WE PURPOSELY REMAINED HIGH ON BASE LEG BEFORE TURNING FINAL KNOWING THE MLG WOULD PASS DIRECTLY UNDER US. WE XED THE 24R LOC THEN TURNED FINAL FOR RWY 24L, ROLLING OUT ON THE S TAXIWAYS. MY FO LOOKED DOWN AND TO HIS R AND SAID TO ME THAT IT APPEARS THE MLG IS LINED UP WITH THE 24L RWY. WE CALLED THE TWR AT THE HARBOR FREEWAY AND THE CTLR ASKED US IF WE STILL HAD THE MLG IN SIGHT. THE FO TOLD THE CTLR WE DID NOT SEE THE MLG FOR THE TIME HE WAS UNDER US. MY FO ASKED THE TWR TO CONFIRM THAT THE MLG IS LINED UP FOR RWY 24R. THE PLT OF THE MLG STATED HE WAS LINED UP FOR RWY 24R. WE HAD THE MLG IN SIGHT AT ALL TIMES EXCEPT WHEN HE PASSED BENEATH US; WE WERE HDG 160 DEG, THE MLG HDG WAS 250 DEG. AFTER SPEAKING WITH THE SUPVR BY PHONE, ATC'S CONCERN REVOLVED AROUND 2 KEY FACTORS: 'FOLLOW' AND 'IN SIGHT'. BEING DIRECTED TO FOLLOW THE MLG AFTER WE WERE CLRED FOR THE 'VISUAL APCH' PRESENTED CONFLICTING INFO. WX WAS OBSCURED SKY VISIBILITY 4 MI. THE MLG AND OUR ACFT WERE NOT IN SIGHT BY THE TWR (AND VICE-VERSA) WHEN WE XED OVER THE MLG THEREFORE THE APCH CTLR WAS OBLIGATED TO GIVE US A NEW VECTOR AWAY FROM A PERCEIVED CONFLICT BECAUSE WE INFORMED ATC WE HAD LOST SIGHT OF THE OTHER ACFT ON A VISUAL APCH. OUR QUESTION IS WHY WE CAN BE CLRED FOR A VISUAL APCH TO FOLLOW AN ACFT ON AN ILS (PARALLEL RWY) WHEN THAT ACFT CAN'T SEE THE RWY, AND IS NOT FOLLOWING ANOTHER ACFT. OUR 'FOLLOW' ACFT WAS ON THE ILS. THE REASON WE PASSED UP THE MLG WAS OUR DISTANCE AND ALT FROM TOUCHDOWN. AS WE TURNED FINAL WE STILL WERE ABOUT 6 MI FROM THE END OF THE 24L RWY AND ABOUT 3000 FT MSL. WE FEEL THE PROCS CTLING VISUAL APCHES PERMITTED BY FOLLOWING AN ACFT ON AN ILS NEED TO BE EXAMINED MORE CLOSELY.

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.