Narrative:

We were en route to dtw when we were cleared to slow to 210 KIAS and descend and maintain 7000 MSL. Captain read back the clearance and 7000 was set in the awi. The controller didn't respond to the captain's readback. Passing 11,000' MSL I noticed an medium large transport crossing from right to left at 10,000' MSL heading approximately 060 degree. Passing 10,500' MSL we heard the controller advise us to maintain 11,000' for traffic at 10,000'. We read back 11,000 and started to climb. We asked the controller if we had been cleared to 7000' MSL and he said no, it was 11,000 but we had already passed 10,500' MSL. No evasive action was necessary. I think the problem was due to miscom. The controller did not challenge our readback if it was in error. But I believe we were cleared to 7000' and the conflict was due to the controller clearing us to 7000' MSL.

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Original NASA ASRS Text

Title: ACR DESCEND BELOW ASSIGNED ALT RESULTING IN LESS THAN STANDARD SEPARATION WITH ANOTHER ACFT.

Narrative: WE WERE ENRTE TO DTW WHEN WE WERE CLRED TO SLOW TO 210 KIAS AND DSND AND MAINTAIN 7000 MSL. CAPT READ BACK THE CLRNC AND 7000 WAS SET IN THE AWI. THE CTLR DIDN'T RESPOND TO THE CAPT'S READBACK. PASSING 11,000' MSL I NOTICED AN MLG XING FROM RIGHT TO LEFT AT 10,000' MSL HDG APPROX 060 DEG. PASSING 10,500' MSL WE HEARD THE CTLR ADVISE US TO MAINTAIN 11,000' FOR TFC AT 10,000'. WE READ BACK 11,000 AND STARTED TO CLIMB. WE ASKED THE CTLR IF WE HAD BEEN CLRED TO 7000' MSL AND HE SAID NO, IT WAS 11,000 BUT WE HAD ALREADY PASSED 10,500' MSL. NO EVASIVE ACTION WAS NECESSARY. I THINK THE PROBLEM WAS DUE TO MISCOM. THE CTLR DID NOT CHALLENGE OUR READBACK IF IT WAS IN ERROR. BUT I BELIEVE WE WERE CLRED TO 7000' AND THE CONFLICT WAS DUE TO THE CTLR CLEARING US TO 7000' MSL.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.