Narrative:

After being given approach clearance, we were intercepting the runway 21L localizer after flying through it. ATC said we were supposed to intercept runway 21R localizer. We though we were supposed to intercept runway 21L localizer (came from djb). After we thought about it, neither one of us remembers being given a runway initially by approach control or when cleared. From the direction we flew in from, we had planned runway 21L. We may have missed being given runway 21R. I'm not really sure. There weren't any other aircraft near to cause a problem.

Google
 

Original NASA ASRS Text

Title: RPTR BELIEVED INITIALLY THAT THEIR ACFT WAS GIVEN A CLRNC TO DTW RWY 21L. AS THEY STARTED TO LINE UP WITH THE RWY, APCH CTL INFORMED THEM THAT THEY WERE GIVEN CLRNC TO RWY 21R. SUBSEQUENTLY, RPTR DOES NOT RECALL IF ACFT WAS EVER GIVEN AN APCH CLRNC TO ANY RWY, LET ALONE RWY 21R.

Narrative: AFTER BEING GIVEN APCH CLRNC, WE WERE INTERCEPTING THE RWY 21L LOC AFTER FLYING THROUGH IT. ATC SAID WE WERE SUPPOSED TO INTERCEPT RWY 21R LOC. WE THOUGH WE WERE SUPPOSED TO INTERCEPT RWY 21L LOC (CAME FROM DJB). AFTER WE THOUGHT ABOUT IT, NEITHER ONE OF US REMEMBERS BEING GIVEN A RWY INITIALLY BY APCH CTL OR WHEN CLRED. FROM THE DIRECTION WE FLEW IN FROM, WE HAD PLANNED RWY 21L. WE MAY HAVE MISSED BEING GIVEN RWY 21R. I'M NOT REALLY SURE. THERE WEREN'T ANY OTHER ACFT NEAR TO CAUSE A PROB.

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.