Narrative:

I was pm at cruise at FL370. We received a TCAS TA and upon reducing navigation display range saw the traffic on the navigation display at our altitude and a range of about 10 mi. I was about to key the microphone to ask if we had traffic when the controller (talking fast) cleared us to FL360. I did not think that the PF was responding fast enough; so I set the new altitude in the FCU; selected open descent mode; and told him to descend right away. I think he then disengaged the autoplt; but I'm not sure. At about 36800 ft we got a TCAS RA 'descend' and at the same time visually acquired the opposite direction traffic. ATC asked the other flight to verify that they were level at FL380; which they did. I think that as they passed overhead the vertical 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 flight path. The PF did not select flight directors off; however I chose not to intervene in this area; as I did not want to start any discussion which might distraction from the immediate task. He had established a good descent and was complying with the TCAS vertical commands and I did not believe there was good reason to interfere. The 'descend' command turned to 'monitor vertical speed;' then 'clear of conflict;' and ATC did not mention the event again. To me; this was a good demonstration of the need to be vigilant at cruise. It is easy to believe that nothing significant is likely to occur at altitude; but this is a case where an immediate response was required.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.