AN ACR CREW APCHING DTW HEARD TRACON ASSIGN THEM 6000 FT. AS THE CAPT REPROGRAMMED THE FMS FOR A RWY CHANGE ATC STATED CLRNC ONLY TO 7000 FT.

Narrative

WE CHECKED ON WITH DTW APPROACH AND EXPECTED RUNWAY 04L AS THE NORMAL RUNWAY FOR OUR ARRIVAL. WHEN WERE HANDED OFF TO THE SECOND-TIER (FINAL APPROACH) CONTROLLER; ATC ASSIGNED US RUNWAY 03R AND WE WERE TOLD TO DESCEND TO 6000 FT. I ACKNOWLEDGED THE ALTITUDE ASSIGNMENT OF 6000 FT AND RUNWAY 03R. I (THE PNF) TOLD MY FO THAT I WAS GOING TO CHANGE THE APPROACH IN THE MCDU TO RUNWAY 03R AND HE HAD THE RADIOS. MY FO ACKNOWLEDGED; AND TOOK OVER THE RADIO WORK. WHILE I WAS FINISHING THE MCDU WORK; THE CONTROLLER AGAIN SAID; 'ACR X; DESCEND TO 6000 FT.' MY FO ACKNOWLEDGED THE ATC ASSIGNED ALTITUDE OF 6000 FT. IT WAS THE SECOND TIME THAT THE SAME ALTITUDE WAS ASSIGNED. I RETURNED FROM PROGRAMMING THE MCDU AND TOOK OVER THE RADIO WORK AT WHICH TIME WE WERE PASSING THROUGH 6600 FT TOWARD OUR ASSIGNED ALTITUDE OF 6000 FT. THEN THE DTW APPROACH CONTROLLER SAID; 'ACR X; STAY AT 7000 FT.' THE FO (FP) BEGAN AN IMMEDIATE LEVEL OFF. I STATED TO ATC; 'YOU ASSIGNED US 6000 FT.' HE (DTW APPROACH) SAID; 'NO; I SAID 7000 FT. CLIMB BACK TO 7000 FT.' WE CLIMBED BACK TO 7000 FT WITHOUT INCIDENT. THERE WERE NO ATC INSTRUCTIONS TO ANY OTHER AIRCRAFT; NO TCAS ALERTS; OR TO THE BEST OF MY KNOWLEDGE; NO LOSS OF SEPARATION. THE APPROACH CONTROLLER NEVER STATED ANYTHING THAT WOULD HAVE LED US TO BELIEVE THAT THERE WERE ANY PROBLEMS WITH THE ALTITUDE CLEARANCE CONFUSION. OUR FLIGHT CONTINUED WITHOUT ANY FURTHER MENTION FROM ATC REGARDING THE CONFUSION OF OUR ALTITUDE ASSIGNMENT. THE APPROACH CONTROLLER WAS HEAVILY TASKED AND EVERYONE WAS FLYING A 'DOUBLE-DOWNWIND' FOR SPACING. BOTH MY FO AND I NOTICED THAT OTHER AIRCRAFT ON THE FREQUENCY WERE CALLED MORE THAN ONCE WITH CLEARANCES; AND THERE MAY HAVE BEEN SOME CONFUSION WITH SIMILAR CALL-SIGNS OR POSSIBLY ANOTHER AIRCRAFT HAD ACKNOWLEDGED OUR 7000 FT ALTITUDE ASSIGNMENT.