POTENTIAL CONFLICT AVOIDED AS TCASII RA PROVIDES EVASIVE ACTION LEVEL OFF INFO TO ACR LGT.

Narrative

CLRED OUT OF 16000 FT TO DSND ON THE EGE ARR. APPROX 12- 15 NM S OF KREMMLING VOR AND AT APPROX 15000 FT; WE GOT A RA ON THE TCASII. IT SAID TO REDUCE THE RATE OF DSCNT. I DID THIS BY RETRACTING THE SPD BRAKES. THE TCASII SCREEN DID SHOW TFC AT 12 O'CLOCK AND 1000 FT. AS THE TARGET AIRPLANE PASSED BENEATH US; I SAW WHAT LOOKED LIKE A TWIN WITH IT'S LIGHTS ON. THE TCASII SCREEN DID SHOW ONE MORE ALT OF 800 FT AS THE AIRPLANE FLEW BENEATH AND BEHIND US. TCASII DEFINITELY SAVED A NMAC ON THIS OCCASION. AFTER DISCUSSING THIS SITUATION WITH THE AREA MGR OF ATC AND THE DEPT OF QUALITY ASSURANCE IN DENVER CTR; I AM CONFIDENT THAT IT WAS NOT AN IFR AIRPLANE. IT MAY; IN FACT; HAVE BEEN A MIL TWIN THAT WAS OPERATING UNDER VFR FLT RULES IN THE AREA AT THE SAME TIME AS OUR FLT. I DO NOT KNOW IF THE MIL PLT EVER SAW US. THE VISIBILITY IN THE CLOUDS WAS MARGINAL VMC AT BEST. A SEE AND AVOID MANEUVER WOULD HAVE BEEN DIFFICULT OR IMPOSSIBLE. DEN CTR RADAR ALT COVERAGE IN THE MOUNTAIN AREAS IS LIMITED. TCASII WORKED AS ADVERTISED.