ATC ASSIGNS CROSS 10 N BUM FO MISUNDERSTANDS TO 30 N BUM AT 8000 FT. CAPT NOT AWARE OF FO PLAN. FLC MISS ALT RESTR BY 2 MI.

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LEVEL 13000 FT; 20 MI S OF BUTLER VOR (BUM). FO WAS THE PF. ZKC ASSIGNS US TO CROSS 10 MI N OF BUM AT 8000 FT AND MAINTAIN 8000 FT. I ACKNOWLEDGE BY READING BACK THE INSTRUCTIONS. THE FO BEGINS THE DSCNT ALMOST IMMEDIATELY WITH A 1000 FPM MINIMUM DSCNT. A SHORT TIME LATER; I NOTICED OUR DSCNT RATE HAS BEEN REDUCED TO 500 FPM; WHICH WOULD NOT ALLOW US TO MEET THE XING RESTR. I POINTED THIS OUT BY TELLING THE FO; 'WE'RE NOT GOING TO MAKE IT AT THAT RATE.' THE FO RESPONDED BY INCREASING HIS DSCNT RATE. AT THIS TIME WE WERE ABOUT 10 MI S OF THE VOR. ABOUT A MIN LATER; I NOTICED AGAIN THAT OUR DSCNT RATE IS 500 FPM. AGAIN I TELL HIM TO INCREASE HIS DSCNT RATE. HE DOES. SINCE WE ARE APCHING MCI AIRSPACE; I TUNE IN AND WRITE DOWN THE ATIS. I LOOK UP; AFTER WRITING DOWN THE ATIS; AND NOTICE WE'RE 0.5 MI FROM THE XING FIX; AND STILL 1200 FT TOO HIGH; WITH A 500 FPM DSCNT. I IMMEDIATELY PULL THE PWR LEVERS TO FLT IDLE; AND PUSH THE NOSE DOWN IN A VAIN ATTEMPT TO GET US TO 8000 FT. BY THE TIME WE REACHED 8000 FT WE WERE 2 MI PAST OUR XING FIX. WHEN I ASKED THE FO WHY HE DIDN'T MAKE THE XING RESTR; HE REPLIED; 'WE STILL HAVE PLENTY OF TIME; IT WAS 30 MI N; RIGHT?' I TELL HIM THAT IT WAS 10 MI N. HE REPLIES THAT HE THOUGHT HE HEARD 30 N. HE WAS WRONG. FORTUNATELY; THERE WAS NO CONFLICTING TFC. AS CAPT; I SHOULD HAVE REALIZED A PROB EXISTED WHEN I HAD TO ADVISE THE FO A SECOND TIME ABOUT THE LEISURELY RATE OF DSCNT. INSTEAD OF MERELY COMMENTING ABOUT THE DSCNT RATE THE SECOND TIME; I SHOULD HAVE QUESTIONED THE FO AS TO WHY HE WAS USING SUCH A MINIMAL DSCNT RATE. IF I HAD; I AM SURE THE MISUNDERSTANDING ON THE PART OF THE FO WOULD HAVE BEEN UNCOVERED AND RESOLVED. ALSO; I SHOULD NOT HAVE DELAYED OBTAINING THE ATIS; GIVEN THIS PARTICULAR SIT; UNTIL WE COMPLIED WITH THE ATC INSTRUCTIONS. ANOTHER FACTOR IN THIS SIT TO BE CONSIDERED; IS THAT OUR TYPE OF AIRPLANE MAKES IT NECESSARY TO WEAR-NOISE-ATTENUATING HEADSETS. THE PROB IS WHEN 1 PLT XMITS; THE OTHER CANNOT HEAR WHAT THAT PLT IS SAYING ON THE RADIO BECAUSE THERE IS NO SIDETONE. HAD OUR EQUIP NOT HAD THIS LIMITATION; THE FO WOULD HAVE HEARD MY READBACK. AND AT THE VERY LEAST; WOULD HAVE QUESTIONED WHETHER ONE OF US HAD NOT MISUNDERSTOOD CTR'S INSTRUCTIONS.