A DSNDING DC10 FLC MISINTERPS THEIR CLRNC AND DSNDS OUT OF THEIR LAST ASSIGNED ALT TOWARDS THE XING ALT DEPICTED ON THE ARR STAR 50 MI NW OF DTW; MI.

Narrative

WE WERE DSNDING INTO DTW ON THE POLAR STAR. WE HAD BEEN CLRED TO 17000 FT FLYING THE STAR TRACK. POLAR INTXN IS NORMALLY CROSSED AT 12000 FT (AS PUBLISHED ON THE STAR). WE WERE DSNDING ON PROFILE (NO PWR) FOR THIS XING (WITH THE CLRNC TO 17000 FT). DSNDING THROUGH FL180 AND ABOUT 18 MI FROM POLAR THE CTLR CLRED US DIRECT TO POLAR INTXN AND; I THOUGHT I HEARD; TO CROSS AT 12000 FT. THERE ARE 2 POSSIBILITIES HERE: EITHER THE CTLR ACTUALLY GAVE US THE ALT; OR I SIMPLY HEARD IT BECAUSE I EXPECTED IT. IN ADDITION; HAVING BEEN CLRED DIRECT; CUT OFF A COUPLE OF MI; AND WE HAD TO KEEP DSNDING IF WE HAD TO CROSS POLAR AT 12000 FT. AS I DSNDED THROUGH ABOUT 16000 FT THE CTLR CALLED US AND SAID WE WERE ONLY CLRED TO 17000 FT. I IMMEDIATELY LEVELED OFF; AND WE RESPONDED THAT WE THOUGHT HE GAVE US DIRECT POLAR AND 12000 FT. THE CTLR THEN CAME BACK AND CLRED US TO 13000 FT AND SWITCHED US OVER TO APCH; WHICH IMMEDIATELY CLRED US TO 12000 FT. (AS A SIDE NOTE: WE NEVER GOT THE 'POLAR AT 12000 FT' RESTR; AND HAVING LEVELED OFF TO CLARIFY THE CLRNC WE WERE TOO HIGH TO CROSS POLAR AT 12000 FT.) WE WERE IN VMC; THERE WAS NO CONFLICTING TFC WE COULD SEE; AND OUR TCASII WAS ON AND SHOWED NO TFC AT ALL. WE CONTINUED TO RWY 21R FOR AN UNEVENTFUL APCH AND LNDG. SUPPLEMENTAL INFO FROM ACN 476640: THE CAPT WAS FLYING AND I DIALED 17000 FT INTO THE ALT WINDOW ON THE AUTOPLT WINDOW AND ARMED IT. WE HAD BEEN TALKING ABOUT THE XING AT 12000 FT. A FEW SECONDS LATER; THE CAPT SAID 12000 FT NOW AT POLAR; AND I WASN'T SURE IF HE SAID POLAR AT 12000 FT; BUT INSTEAD OF VERIFYING THAT ALT WITH ZOB; I WENT WITH THE CAPT. SINCE HE SEEMED POSITIVE THAT'S WHAT WE GOT. INSTEAD OF AGREEING WITH THE CAPT ON THE 12000 FT AT POLAR; I SHOULD'VE QUESTIONED AND VERIFIED THE ALT WITH ZOB.