POSSIBLE OPERROR IN CLRNC FOR DSCNT THROUGH OCCUPIED ALT. POTENTIAL CONFLICT LTSS.

Narrative

WE WERE DSNDING FROM FL390 TO FL370. WE HAD REQUESTED DSCNT IN ORDER TO MEET EXPECTED ALT RESTRICTIONS ON THE DADES 1 ARR INTO TAMPA INTL. RATHER THAN INITIATE AN IDLE DSCNT; I ELECTED TO USE THE CRUISE DSCNT CAPABILITY OF THE FMC. AT ABOUT 38000 FT MSL I SAW AN ACFT; ACR ABOUT THE SIZE OF AN LGT; DIRECTLY AHEAD AND SLIGHTLY BELOW FLASHING HIS LNDG LIGHT. SHORTLY AFTER THAT WE PASSED DIRECTLY OVER HIM AT LESS THAN 1000 FT. TCASII WAS ON BUT WE RECEIVED NO RA OR EVEN A TA. ONLY AFTER THE FACT DID WE RECEIVE AVOIDANCE VECTORS AND ALT AMENDMENT. THERE WAS NO INDICATION THAT ANYTHING WAS WRONG UNTIL AFTER THE FACT. IF I HAD STARTED AN IDLE DSCNT INSTEAD OF A CRUISE DSCNT WE WOULD HAVE COLLIDED. ATC INDICATED THAT IT WAS THEIR PROB AND THEY WERE INVESTIGATING THE PROC. I WAS VERY DISTURBED BY THE FACT THAT WE GOT NO REACTION OF ANY KIND FROM THE TCASII UNIT ON OUR ACFT. SELF TEST INDICATED THAT IT WAS WORKING PROPERLY. THE OTHER ACFT WAS LEVEL AT FL370; OUR CLRED TO ALT. SUPPLEMENTAL INFO FROM ACN 235067: WE WERE GIVEN AN IMMEDIATE 90 DEG R TURN; WHICH AGAIN I THINK PUT US IN CONFLICT WITH ANOTHER ACFT. WE SHOULD HAVE BEEN CLBED BACK TO FL390; BUT WE WERE KEPT AT FL380. VERY POOR.