AN L1011 ON APCH TO LAX RWY 25R WAS ADVISED TO KEEP ACR Y B757 IN SIGHT MAKING A VISUAL APCH TO RWY 25L AND 'NOT TO PASS IT'. THE L1011 GAINED ON THE B757 AND PASSED IT 1.5 MI FROM TOUCHDOWN WHEN THE B757 SLOWED FOR LNDG. L1011 CREW WAS ASKED TO CALL THE TWR SUPVR WHO LATER SAID THE FAC OPERATION 'WAS LEGAL.'

Narrative

DURING APCH VIA PARADISE 2 TO LAX; INSIDE ARNES INTXN; SOCAL RESTRICTS OUR FLT TO 7000 FT AND INSTRUCTS US TO CALL RWY 25R IN SIGHT; PLUS ANOTHER ACR FLT IS TURNING ONTO THE RWY 25L APCH. UNABLE TO ANSWER BECAUSE OF RADIO TFC; WE ARE FINALLY CLRED TO INTERCEPT RWY 25R LOC BUT NOT TO PASS ACR Y FLT. AT THE POINT WE ARE EVEN WITH THE ACR Y B757 ON RWY 25L APCH. SLOWED TO APCH SPEED AND VERY HIGH ON GLIDEPATH. WE MAINTAINED EVEN POS WITH ACR Y B757 UNTIL INSIDE TWO MILES WHEN ACR Y SLOWS. AS PLT FLYING I DID NOT HAVE ACR Y IN SIGHT BUT CAPT DID; UNTIL HE SLOWED AND WE WENT AHEAD. TWR ASKED IF WE HAD ACR Y IN SIGHT AND WE REPLIED 'NO' AT WHICH TIME ACR Y ADVISED WE WERE IN SIGHT. WE WERE ADVISED TO CALL TWR AT THE GATE. THIS IS AN UNSATISFACTORY SIT FOR ALL INVOLVED. MINIMUM SPEED IS MINIMUM SPEED AND A B757 HAS A LOWER SPEED THAN L-1011. CLOSE PROX OF LAX RWYS 25R & 25L MADE TWO LARGE ACFT TOO CLOSE FOR SAFETY. LAX TWR ADVISED IT IS LEGAL. SUPPLEMENTAL INFO FROM ACN 403809: I WAS TOLD NOT TO PASS THE B757. AT 1 1/2 MI FROM LNDG WE WERE EVEN WITH THE B757. WE WERE AT MINIMUM SPEED GETTING ON THE GLIDESLOPE. I CAME BACK VISUALLY IN THE COCKPIT TO SEE HOW THE COPLT (FLYING) WAS DOING; WHEN I TURNED BACK TO OBSERVE THE B757 HE WAS GONE; HAVING PULLED THE PWR TO GET BEHIND US. THE LAS TWR SUPVR TOLD ME I VIOLATED THE CLRNC. WITHIN 1 MI TO TOUCHDOWN THERE IS NO WAY I CAN STAY BEHIND; EVEN WHEN I'M AT MINIMUM SPEED AND A B757 PULLS THE PWR.