Narrative:

We were departing IMC with showers and layered clouds. I do not recall if we were IMC at the time; but ATC was highly congested; with blocked calls and missed calls. We had finished one of the several step climbs and were level at an assigned flight level (I believe FL240); on autoplt; and had finished setting an interim cruise power. We were expecting another climb to our requested altitude. At some point thereafter; we heard a controller request us to descend to FL240 and for another aircraft to climb to FL270. Since we were already at the assigned flight level; there was confusion in our cockpit and I hesitated to do anything without clarification with ATC. The frequency was jammed with other communications and my copilot could not get through to clarify the communication. Shortly thereafter; the controller repeated the request; although part of the request was again blocked by another transmission. Our TCAS suddenly reported a conflict and I disengaged the autoplt and descended below our assigned flight level under an assumption that another airplane was descending into our flight level. I cannot recall how far below assigned altitude; but I believe it was less than 1000 ft. There were no aircraft showing on the display below us. Once we showed the conflict behind us; I re-engaged the autoplt and climbed back to the assigned altitude. We asked the controller what happened but was unclr in the responses. I think a supervisor may have been on the frequency as there may have been 2 different voices. I also heard the other aircraft report to the controller that they had us in sight during the crossing of paths (he did not indicate how close we were). I do not know what the separation from the other aircraft may have been and whether we reached a critical conflict situation.

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Original NASA ASRS Text

Title: CE500 FLT CREW RPTS A POSSIBLE ALTDEV RESULTING IN A TCAS RA.

Narrative: WE WERE DEPARTING IMC WITH SHOWERS AND LAYERED CLOUDS. I DO NOT RECALL IF WE WERE IMC AT THE TIME; BUT ATC WAS HIGHLY CONGESTED; WITH BLOCKED CALLS AND MISSED CALLS. WE HAD FINISHED ONE OF THE SEVERAL STEP CLBS AND WERE LEVEL AT AN ASSIGNED FLT LEVEL (I BELIEVE FL240); ON AUTOPLT; AND HAD FINISHED SETTING AN INTERIM CRUISE PWR. WE WERE EXPECTING ANOTHER CLB TO OUR REQUESTED ALT. AT SOME POINT THEREAFTER; WE HEARD A CTLR REQUEST US TO DSND TO FL240 AND FOR ANOTHER ACFT TO CLB TO FL270. SINCE WE WERE ALREADY AT THE ASSIGNED FLT LEVEL; THERE WAS CONFUSION IN OUR COCKPIT AND I HESITATED TO DO ANYTHING WITHOUT CLARIFICATION WITH ATC. THE FREQ WAS JAMMED WITH OTHER COMS AND MY COPLT COULD NOT GET THROUGH TO CLARIFY THE COM. SHORTLY THEREAFTER; THE CTLR REPEATED THE REQUEST; ALTHOUGH PART OF THE REQUEST WAS AGAIN BLOCKED BY ANOTHER XMISSION. OUR TCAS SUDDENLY RPTED A CONFLICT AND I DISENGAGED THE AUTOPLT AND DSNDED BELOW OUR ASSIGNED FLT LEVEL UNDER AN ASSUMPTION THAT ANOTHER AIRPLANE WAS DSNDING INTO OUR FLT LEVEL. I CANNOT RECALL HOW FAR BELOW ASSIGNED ALT; BUT I BELIEVE IT WAS LESS THAN 1000 FT. THERE WERE NO ACFT SHOWING ON THE DISPLAY BELOW US. ONCE WE SHOWED THE CONFLICT BEHIND US; I RE-ENGAGED THE AUTOPLT AND CLBED BACK TO THE ASSIGNED ALT. WE ASKED THE CTLR WHAT HAPPENED BUT WAS UNCLR IN THE RESPONSES. I THINK A SUPVR MAY HAVE BEEN ON THE FREQ AS THERE MAY HAVE BEEN 2 DIFFERENT VOICES. I ALSO HEARD THE OTHER ACFT RPT TO THE CTLR THAT THEY HAD US IN SIGHT DURING THE XING OF PATHS (HE DID NOT INDICATE HOW CLOSE WE WERE). I DO NOT KNOW WHAT THE SEPARATION FROM THE OTHER ACFT MAY HAVE BEEN AND WHETHER WE REACHED A CRITICAL CONFLICT SIT.

Data retrieved from NASA's ASRS site as of January 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.