ACR UNABLE TO COMPLY WITH ATC ALT ASSIGNMENT. COMPLAINT REFERENCE ATC PROC INTO SLC FROM THE WEST.

Narrative

FLYING ACR X ON IFR FLT TO SLC AT FL370. ON ZLC FREQ; 128.55; CLRED TO CROSS 30 MI W OF SLC VOR AT 15000'. WE WERE APPROX 80 MI W AT THE TIME; SO INITIATED A DSCNT WITH SPD BRAKES DEPLOYED AND DSNDED AT APPROX 4000 FPM IN ORDER TO COMPLY WITH XING RESTRICTION. TSTMS IN THE AREA CAUSED A NEED FOR DEVIATIONS FROM VECTOR HDGS. AT AROUND 17600' ATC TOLD US TO LEVEL AT 17000'. I SET THE ALT IN THE MASTER CTL PANEL ALT WINDOW; BUT DUE TO THE EXCESSIVE DSCNT RATE; THE AUTOPLT FAILED TO CAPTURE 17000' AND THE DSCNT CONTINUED UNTIL I DISCONNECTED THE AUTOPLT AND LEVELED THE ACFT AT AROUND 16600'. I THEN CLBED BACK TO 17000' AND RECONNECTED THE AUTOPLT. ATC DID NOT MENTION THE LOSS OF ALT AND THE FLT/APCH TO SLC CONTINUED W/O INCIDENT. APCHING SLC FROM THE W; ATC IS OFTEN SLOW TO GIVE DSCNT CLRNC; WHICH THEN CAUSES HIGHER THAN NORMAL DSCNT RATES; USUALLY COMPOUNDED BY THE FACT THAT THERE IS OFTEN A STRONG TAILWIND IN THAT AREA. ALSO; THERE IS NO STANDARD XING POINT; SO FLT PLANNING IS NOT POSSIBLE UNTIL THE MOMENT THE CLRNC IS RECEIVED. IN THIS INCIDENT; EVEN IF THE AUTOPLT HAD CAPTURED 17000'; I DON'T BELIEVE THAT THE ACFT COULD HAVE LEVELED AT THAT ALT W/O CAUSING DISCOMFORT AND EVEN HARM TO THE PAX AND F/A'S. SUPPLEMENTAL INFO FROM ACN 92312: WE HAD A 65 KT TAILWIND AT FL370; AND WE BEGAN OUR DSCNT IMMEDIATELY WITH FULL SPD BRAKES TO MAKE THE RESTRICTION. CTLR ISSUED DSCNT CLRNC WITH RESTRICTION TOO LATE WITH EXISTING CONDITIONS (I.E.; TAILWIND). CTLR ISSUED A NEW ALT THAT WAS NEARLY IMPOSSIBLE TO MAKE WITH EXISTING CONDITIONS (I.E.; 4000 FPM RATE OF DSCNT). PLTS SHOULD HAVE INFORMED CTLRS OF PROB IN LEVELING OFF IN THAT SHORT OF TIME.