AN ACR LGT CREW WAS DSNDING TO 10000 FT AT 17 MI. THE CLRNC WAS 17000 FT AT 10 MI.

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I WAS FLYING THE ACFT. CAPT WAS ON THE RADIOS. THE ACFT; AN LGT; WAS ON AUTOPLT WITH LNAV AND VNAV MODES ENGAGED. DURING DSCNT INTO SLC; THE CTLR GAVE US A XING RESTRICTION TO CROSS 10 MI E OF FFU AT 17000 FT. AS I WAS SETTING A WAYPOINT 11 MI E OF FFU (I USUALLY USE AN EXTRA MILE AS A PAD); THE CAPT ASKED FOR CLARIFICATION OF THE CLRNC; TO CONFIRM 17 MI E AT 10000 FT. THE CTLR REPLIED IN THE AFFIRMATIVE; SO I CHANGED THE WAYPOINT TO 18 MI EAST OF FFU AT 10000 FT. AT THE VNAV COMPUTED TOP OF DSCNT POINT; THE ACFT STARTED DOWN. WE WERE SUBSEQUENTLY GIVEN A VECTOR OF 220 DEGS FOR SPACING. DURING THE DSCNT; I BEGAN TO BECOME CONCERNED THE LOW ALT E OF THE WASATCH MOUNTAINS. JUST AS I WAS ABOUT TO SPEAK UP; THE CTLR ASKED ABOUT OUR ALT (WE WERE JUST PASSING 15500 FT). THE CAPT REPLIED THAT WE UNDERSTOOD WE WERE CLRED TO 10000 FT. THE CTLR TOLD US TO LEVEL AT 15000 FT; WHICH WAS NO PROBLEM SINCE I HAD TAKEN THE ACFT OFF AUTOPLT AND BEGAN LEVELING OFF AS SOON AS HE SPOKE. WE WERE THEN CLRED DIRECT TO FFU; AND THE REST OF THE FLT WENT SMOOTHLY. SO; YET ANOTHER CASE OF MISCOM RESULTING IN AN ALTDEV (I READ CALLBACK). SOMEONE UNFAMILIAR WITH THE TERRAIN AND A CLOUDY NIGHT AND THIS SCENARIO COULD HAVE HAD A TRAGIC CONCLUSION. ALSO; ANOTHER GOOD REASON TO ACCELERATE DEVELOPMENT OF DATA LINK COM. THE SKIES ARE TOO CROWDED FOR BUSY TERMINAL AREAS THAT PROVIDE ALT AND AIRSPD RESTRICTIONS IN PRINT AT GIVEN PINTS TO HELP THESE OVERWORKED CTLRS COPE WITH THE EVER-INCREASING VOLUME OF TFC CONVERGING ON THE LARGER TERMINAL AREAS. ASK ANY PLT (OR CTLR FOR THAT MATTER) ABOUT A WELL-PROCEDURALIZED APCH AND DEP SYS; LIKE ATLANTA; FOR INSTANCE. THE SYS WORKS WELL WHEN EVERYONE KNOWS WHAT TO EXPECT; AND EVERYONE IS BEING PREDICTABLE. A MOUNTAINOUS AREA IS NO PLACE FOR AN OLD FASHIONED ATC SYS. SUPPLEMENTAL INFO FROM ACN 222299: I READ BACK THE CLRNC AND GOT IT WRONG. THE CTR GAVE US THE CLRNC AGAIN. I READBACK THE CLRNC AND GOT IT WRONG. THE CTR GAVE US THE CLRNC AGAIN. I READ BACK THE CLRNC. THE CTR SAID 'ROGER.' I WATCHED THE COPLT ENTER MY FIRST READBACK THAT WAS WRONG INTO THE FMS AND MODE CTL PANEL. IT DIDN'T REGISTER THAT IT WAS THE WRONG RESTRICTION.