PLTDEV.

Narrative

WHILE FLYING ILS RWY 30R AT STL. AFTER GS INTERCEPT AT APPROX 4500 FT MSL; NOTICED ACFT ON LDA RWY 30L AT STL ON TCASII. APPEARED TO BE CLOSING ON OUR ACFT. APCH CTL DID TELL US OF TFC. ACFT SYMBOL APPEARED ON TCASII TO BE TOUCHING OUR OWN ACFT SYMBOL AT THE SAME ALT IN A 6 MI MODE. AT THIS POINT I NOTICED THAT THE LIGHT INTENSITY REFLECTING FROM THE CLOUDS INCREASED SIGNIFICANTLY. I FELT THAT THE INCREASED LIGHT WAS COMING FROM THE OTHER ACFT'S LNDG LIGHTS; THOUGH WE WERE IMC AND COULD NOT SEE THE OTHER ACFT. TCASII AT NO TIME ISSUED EITHER A TA OR RA. I INCREASED AIRSPD TO 210 KTS (FROM 170 KTS) TO INCREASE SEPARATION AND THE INTENSITY OF THE LIGHT REFLECTED FROM THE CLOUDS DECREASED. I THEN SLOWED THE ACFT BACK TO 170 KTS. AT THAT POINT WE BEGAN SLOWING FOR FINAL APCH AND LNDG. NO MENTION OF OUR SPD FLUCTUATION WAS MADE BY APCH CTL OR TWR AND THE APCH AND LNDG WERE MADE NORMALLY FROM THIS POINT. I FEEL THAT A LOSS OF SEPARATION OCCURRED AND THAT THE ACFT CONDUCTING THE LDA RWY 30L AT THAT TIME WAS NOT ON CTRLINE OF HIS/HER LOC. I WAS FLYING THE ILS WITH THE FLT DIRECTOR COUPLED TO THE ILS. THE AUTOPLT WAS DISENGAGED. I FEEL THE REASON THE TCASII DID NOT ISSUE ANY ADVISORIES IS BECAUSE THE CLOSURE RATE BTWN THE ACFT WAS NOT HIGH ENOUGH TO ACTIVATE IT. TO CORRECT THIS PROB; I FEEL IT WOULD BE NECESSARY TO DISCONTINUE SIMULTANEOUS ILS RWY 30R AND LDA RWY 30L APCHS TO STL.