A319 FLT CREW RECEIVED A TCAS ADVISORY FOR CO-ALT TFC. ATC ISSUED A DESCENT CLRNC AND TCAS 'RA' ALSO COMMANDED A DESCENT.

Narrative

I WAS PM AT CRUISE AT FL370. WE RECEIVED A TCAS TA AND UPON REDUCING NAV DISPLAY RANGE SAW THE TFC ON THE NAV DISPLAY AT OUR ALT AND A RANGE OF ABOUT 10 MI. I WAS ABOUT TO KEY THE MIKE TO ASK IF WE HAD TFC WHEN THE CTLR (TALKING FAST) CLRED US TO FL360. I DID NOT THINK THAT THE PF WAS RESPONDING FAST ENOUGH; SO I SET THE NEW ALT IN THE FCU; SELECTED OPEN DSCNT MODE; AND TOLD HIM TO DSND RIGHT AWAY. I THINK HE THEN DISENGAGED THE AUTOPLT; BUT I'M NOT SURE. AT ABOUT 36800 FT WE GOT A TCAS RA 'DSND' AND AT THE SAME TIME VISUALLY ACQUIRED THE OPPOSITE DIRECTION TFC. ATC ASKED THE OTHER FLT TO VERIFY THAT THEY WERE LEVEL AT FL380; WHICH THEY DID. I THINK THAT AS THEY PASSED OVERHEAD THE VERT SEPARATION WAS 400 FT ON THE TCAS. I REALLY DO NOT KNOW WHAT THE SEPARATION LOOKED LIKE VISUALLY; AND I WAS MOST INTERESTED IN MONITORING OUR FLT PATH. THE PF DID NOT SELECT FLT DIRECTORS OFF; HOWEVER I CHOSE NOT TO INTERVENE IN THIS AREA; AS I DID NOT WANT TO START ANY DISCUSSION WHICH MIGHT DISTR FROM THE IMMEDIATE TASK. HE HAD ESTABLISHED A GOOD DSCNT AND WAS COMPLYING WITH THE TCAS VERT COMMANDS AND I DID NOT BELIEVE THERE WAS GOOD REASON TO INTERFERE. THE 'DSND' COMMAND TURNED TO 'MONITOR VERT SPD;' THEN 'CLR OF CONFLICT;' AND ATC DID NOT MENTION THE EVENT AGAIN. TO ME; THIS WAS A GOOD DEMO OF THE NEED TO BE VIGILANT AT CRUISE. IT IS EASY TO BELIEVE THAT NOTHING SIGNIFICANT IS LIKELY TO OCCUR AT ALT; BUT THIS IS A CASE WHERE AN IMMEDIATE RESPONSE WAS REQUIRED.