Narrative:

During descent into toronto, our gulfstream iv, was directed to descend and maintain FL230 (or so we thought). We read back the clearance, began our dsnct, and set 23000 ft in our altitude select window. Our altimeters remained set at 29.92. As we descended through FL280, the center controller asked us our altitude. We reported through FL255 for FL230. The controller advised that we had been assigned FL280, but to continue descent to 12000 ft. He indicated that he may have missed our original readback, but seemed unconcerned about possible conflicts. The remainder of our flight was uneventful.

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Original NASA ASRS Text

Title: A CPR GULFSTREAM IV CREW DSNDED THROUGH ITS ASSIGNED ALT. ERROR ADMITTED.

Narrative: DURING DSCNT INTO TORONTO, OUR GULFSTREAM IV, WAS DIRECTED TO DSND AND MAINTAIN FL230 (OR SO WE THOUGHT). WE READ BACK THE CLRNC, BEGAN OUR DSNCT, AND SET 23000 FT IN OUR ALT SELECT WINDOW. OUR ALTIMETERS REMAINED SET AT 29.92. AS WE DSNDED THROUGH FL280, THE CTR CTLR ASKED US OUR ALT. WE RPTED THROUGH FL255 FOR FL230. THE CTLR ADVISED THAT WE HAD BEEN ASSIGNED FL280, BUT TO CONTINUE DSCNT TO 12000 FT. HE INDICATED THAT HE MAY HAVE MISSED OUR ORIGINAL READBACK, BUT SEEMED UNCONCERNED ABOUT POSSIBLE CONFLICTS. THE REMAINDER OF OUR FLT WAS UNEVENTFUL.

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.