MD80 DELAYS SWITCH TO TOWER DUE TO POTENTIAL FOR AN RA FROM ACFT NOT APPARENT TO APCH CTL.

Narrative

ON FINAL TO RWY 26L AT IAH WE WERE CLRED THE VISUAL APCH TO CROSS JEPN1 AT OR BELOW 2000 FT; WHICH SEEMED A BIT UNUSUAL. APCH WAS ALSO CALLING OUT PARALLEL TFC ON THE APCH TO RWY 27; WHICH WE HAD IN SIGHT; AND WAS BEING DISPLAYED ON TCAS. THERE WAS OTHER TFC BEING DISPLAYED ON TCAS AHEAD; TO THE R; AND BELOW OUR ALT BY ABOUT 1000 FT THAT APCH CTL WAS NOT CALLING OUT. APCH TRIED TO GIVE US A FREQ CHANGE AS WE WERE NEARING THE NON-ALERTED TO TFC; WHICH I DECLINED STATING THAT I'D LIKE TO STAY ON HIS FREQ IN THE EVENT WE RECEIVED AN RA; WHICH WE DID NOT. WE LEVELED AT 2000 FT AND ONCE CLR OF THE CONFLICT I ACCEPTED THE FREQ CHANGE TO TWR AND COMPLETED THE REMAINDER OF THE FLT UNEVENTFULLY. NEITHER THE FO NOR MYSELF EVER SAW THE ACFT THAT PASSED DIRECTLY BELOW US WITH THE MINIMUM ALT BEING DISPLAYED AS 700 FT. THE COCKPIT WAS VERY BUSY THIS ENTIRE TIME WATCHING THE TFC APCH CTL DID ALERT US TOO; CONFIGURING THE ACFT; TURNING TO FINAL; CHKING THE UNUSUAL ALT CLRED TO; THE POTENTIAL FREQ CHANGE; AND WATCHING TCAS FOR THE ACFT WE WERE NOT ALERTED TO BY APCH CTL; AND TRYING TO LOCATE THAT ACFT. AFTER LNDG AND THINKING ABOUT THE INCIDENT I'M SURE APCH CTL NEVER SAW THE ACFT THAT WAS A POTENTIAL HAZARD AND AT THE TIME; WITH ALL THAT WAS GOING ON; I WAS NOT CLR TO APCH ABOUT THE POS OF THE ACFT WE WERE CONCERNED WITH. AS STATED EARLIER; WE DID NOT RECEIVE AN RA. THERE WAS AN FAA INSPECTOR ON THE JUMPSEAT; WHO; AFTER LNDG SAID HE SAW THE ACFT CROSS BELOW US AND THAT HE WAS GOING TO TALK TO THE APCH CTLR ABOUT THE INCIDENT. SUPPLEMENTAL INFO FROM ACN 794439: HAD WE CONTINUED A NORMAL DSCNT FOR JEPN1 WE VERY LIKELY WOULD HAVE IMPACTED THE SMALL ACFT.