DC9-50 FO FAILED TO MAKE STAR XING FIX DUE MISS COMPUTING THE DSCNT RATE.

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ZMP CLRED US TO DSND TO CROSS TWINZ INTXN AT 11000 FT ON THE EAU CLAIRE FIVE ARR (EAU.EAU5). THE FO WAS FLYING THE ACFT AND DELAYED INITIATING THE DSCNT BEYOND THE POINT THAT I WOULD HAVE DSNDED; PRESUMABLY COUNTING ON A STRONGER HEADWIND TO AID IN MAKING THE RESTR. I DISCUSSED THE USE OF A DSCNT PLANNING COMPUTER; BUT HE PREFERRED TO DO THE MATH IN HIS HEAD. WE WERE BEHIND IN THE DSCNT AND MAKING SOME IMPROVEMENT WHILE I WAS PERFORMING THE DSCNT CHK. THE FO INCREASED THE RATE OF DSCNT TO A MAX OF APPROX 8000 FPM DURING THE LATTER STAGES OF THE DSCNT; BUT ULTIMATELY FAILED TO MAKE THE RESTR BY ABOUT 3000 FT. I INFORMED ZMP THAT WE WOULD BE HIGH AT TWINZ INTXN. I SHOULD HAVE INTERVENED EARLIER AND BEEN MORE EMPHATIC ABOUT THE NEED TO INCREASE THE RATE OF DSCNT WITH AN EARLIER DEPLOYMENT OF FULL SPOILERS. SUPPLEMENTAL INFO FROM ACN 520939: NEARING FL230; ONE OF OUR FLT ATTENDANTS CAME UP TO THE FLT DECK AND ENGAGED US IN CONVERSATION. THE CAPT AND I CONTINUED TO CONVERSE WITH THE FLT ATTENDANT. AT ABOUT 18000 FT; THE FLT ATTENDANT LEFT THE FLT DECK. AT THE SAME TIME; IT WAS BECOMING CLR THAT I WASN'T GOING TO MAKE TWINZ AT 11000 FT AT OUR CURRENT DSCNT RATE SO I DEPLOYED THE SPD BRAKES. ATC INQUIRED AS TO WHETHER WE WERE GOING TO CROSS TWINZ AT 11000 FT. THE CAPT REPLIED THAT WE WERE DOING OUR BEST BY DSNDING AT APPROX 6000 FPM. SHORTLY BEFORE XING TWINZ AT ABOUT 14000 FT; THE CAPT TOLD ATC WE WEREN'T GOING TO MAKE THE RESTR. ATC THEN CLRED US TO JUST DSND TO 11000 FT.