AN HS125-700 CREW MISUNDERSTOOD AN ATC RADAR CTLR'S INSTRUCTION TO LEVEL AT FL300 AND LEVELED AT FL310 CAUSING A PLTDEV FOR TFC SEPARATION.

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WE DEPARTED SLN. WE WERE GIVEN CLRNC DURING THE CLB TO 'CLB AND MAINTAIN FL310.' WE REPLIED WITH A 'MAINTAIN FL310.' WHILE CONTINUING THE SLOW CLB; AT FL285; WE RECEIVED THE FOLLOWING INSTRUCTIONS -- OR WHAT WE BOTH BELIEVED TO BE THE FOLLOWING INSTRUCTIONS: 'ADVISE FL300 FOR FL310 FOR TFC ABOVE.' WE RESPONDED WITH SOMETHING LIKE 'OK...ADVISE FL300' OR 'OK...CHK WITH YOU AT FL300' (NOT COMPLETELY CLR WITHOUT TAPE CONFIRMATION). WE ARE SURE; HOWEVER; THERE WAS NO MENTION OF 'MAINTAIN' IN OUR READBACK. SINCE THE CTLR NEVER QUESTIONED OUR READBACK NOR DID HE RESPOND; WE ASSUMED WE HAD HEARD THE INSTRUCTION CLRLY AND THUS RESPONDED CORRECTLY. OUR PERCEPTION OF THE ATC INSTRUCTION WAS THAT THE CTLR WAS BEING PROACTIVE IN POSSIBLY ALLOWING US TO CONTINUE THE SLOWER CLB ONCE TFC WAS CLR; THUS HIS REQUEST TO 'ADVISE FL300 FOR FL310 FOR TFC.' WE THOUGHT THIS WAS JUST FOR HIS INFO TO GET US TO A HIGHER ALT. THE PROB AROSE PRIOR TO LEVELING OFF AT FL310. ONE MISTAKE MADE BY THIS CREW WAS THE LATE CALL GOING THROUGH FL300. WE HAD MISTAKENLY NOT REMEMBERED TO 'ADVISE FL300' UNTIL FL304. FROM WHAT WE CAN RECALL; THE CTLR WAS GIVING INSTRUCTIONS TO SOMEONE ELSE UNTIL WE WERE AT FL308. IMMEDIATELY AFTER TALKING WITH THE OTHER ACFT; HE BEGAN TO INQUIRE ABOUT OUR ALT AS PREVIOUSLY MENTIONED. AS WE WERE CAPTURING OUR ALT; THE CTLR CAME ON AND ASKED US WHAT ALT WE WERE AT. WE RPTED TO HIM THAT WE WERE CAPTURING FL310. HE THEN TOLD US THAT WE WERE SUPPOSED TO BE AT FL300 DUE TO TFC AND THAT HE INSTRUCTED US TO DO SO EARLIER DURING THE RADIO XMISSION AT FL285 IN THE CLB. AT THIS POINT; HE SAID TO DISREGARD AND MAINTAIN FL310 BECAUSE WE WERE CLR OF TFC. WE MENTIONED TO HIM THAT THERE MUST HAVE BEEN A MISUNDERSTANDING; HOWEVER; AFTER A BRIEF PAUSE WE WERE GIVEN A PHONE NUMBER TO CALL ZKC. AFTER THE FLT; WE IMMEDIATELY CALLED ZKC AND SPOKE WITH THE SUPVR. WE TALKED ABOUT NUMEROUS ISSUES INCLUDING: WHAT WAS HEARD ON THE TAPES; THE PROCESS TO EXPECT; AND WHY THEY ARE REQUIRED TO RPT THIS. SHE WAS VERY HELPFUL AND GAVE US THE CONTACT NAMES AND NUMBERS WE WOULD NEED. DISCUSSION OF THE TAPES: SHE DISCUSSED THE INFO THE TAPES CONTAINED. OUR (THE PLT'S) CONCLUSION IS THAT THERE WAS A HUGE MISUNDERSTANDING WITH THE INITIAL CALL FROM ATC AND THEN WITH THE SUBSEQUENT READBACK. SHE TOLD US THAT THE INITIAL CALL WAS SOMETHING ALONG THE LINES OF 'REVISE AND MAINTAIN FL300 FOR FL310 FOR TFC.' THIS IS WHEN WE DID NOT HEAR THE WORD 'MAINTAIN' AND MISCONSTRUED 'REVISE' FOR 'ADVISE.' ONCE AGAIN SHE SAID THE TAPES INDICATED WE DID NOT READ BACK THE WORD 'MAINTAIN.' HOWEVER; BECAUSE THE ACFT SEPARATION OCCURRED THEY HAVE TO PROCESS POSSIBLE PLTDEV ACTION. THIS PROB OCCURRED DUE TO A MISUNDERSTOOD CLRNC AND READBACK. WE (THE PLTS) THOUGHT WE HAD HEARD ONE THING AND RESPONDED. AT THAT POINT; THE CTLR TOOK THAT READBACK AS AN ACKNOWLEDGEMENT. UNFORTUNATELY; WE BOTH PERCEIVED THE INSTRUCTION/READBACK DIFFERENTLY.