DC10 ON FINAL APCH TO RWY 12 IAD. FREQ CONGESTION INTERFERES WITH LDNG CLRNC. AFTER 5 RADIO CALLS PIC ELECTS TO MAKE A MISSED APCH. POTENTIAL CONFLICT WITH TFC DEPARTING RWY 19R.

Narrative

WE WERE CLRED FOR ILS RWY 12 IAD BY APCH. TWR FAILED TO RESPOND TO 4 OR 5 OF OUR CALLS AND BELOW 100 FT AGL WE EXECUTED A GAR. THERE WERE 2 TWR FREQS IN USE AT THIS TIME AND TWR WAS BUSY HANDLING ANOTHER GAR ACFT AND NUMEROUS OTHER TARGETS INFLT AND ON THE GND. CLBING THROUGH APPROX 300-400 FT AGL I (SO) OBSERVED ANOTHER ACR B737 CONVERGING WITH US OFF OF RWY 19R. I CALLED OUT THE TFC BEFORE WE GOT A TA FROM THE TCASII. THE CAPT TOOK EVASIVE ACTION TO AVOID A COLLISION. WE LANDED UNEVENTFULLY. THE TWR CTLR APPEARED TO HAVE BEEN MOMENTARILY SATURATED AS WE WERE APCHING THE RWY. HAVING 2 SEPARATE FREQS FOR CONVERGING RWYS ADDED TO THE PROB AS WE WERE UNAWARE THAT THE B737 WAS COMING OFF OF RWY 19R ON A CONVERGING FLT PATH. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CALLED BACK AND SAID THAT THE PIC HAD TALKED WITH ATC AFTER THE EVENT. HE WAS NOT PRIVY TO ALL THE CONVERSATION. THERE WERE A COUPLE OF REASONS FOR THE MISSED APCH. EVEN THOUGH THE VISIBILITY WAS RPTED AS 5 MI; IT WAS HAZY AND THE ARPT WAS NOT THAT VISIBLE. THE CREW ALSO FELT CONFUSED AS THERE HAD BEEN AN ACFT ON THE RWY AND THEY HEARD SOMEONE GAR. (DIDN'T KNOW WHERE.) THE TWR CTLR WAS 'FIXATED' ON THAT ACFT AND DIDN'T EVEN REALIZE THAT THE SUBJECT ACFT LNDG WAS TRYING TO GET LNDG CLRNC. THE CREW JUST 'DIDN'T FEEL RIGHT' ABOUT CONTINUING ON TO A LNDG UNDER THESE CIRCUMSTANCES. THE PIC AND FO HAD BEEN INTO IAD QUITE FREQUENTLY THOUGH THIS WAS THE FIRST TIME THE SO HAD FLOWN WITH THIS CREW.