Narrative:

East of gij, ZAU told me to descend to 13000 ft. Sometime during the descent, I was told to go to ZOB and did so. After checking in with ZOB and informing him I was descending to 13000 ft, the controller asked my rate of descent. I told him it was 2100 FPM and he told me to 'maintain fifteen.' I answered, 'roger, maintain fifteen.' I thought he meant 15000 FPM and it didn't occur to me that he might mean one five thousand. I guess it was because he had just asked my rate of descent and the use of fifteen instead of one-five. I should have asked for verification. I assumed the change in rate of descent was for traffic and, of course, this has occurred many times before. At about 14200 ft, the controller asked me if I received the altitude and at this point I don't recall how the altitude was said and before I could answer he gave me a climb to 15000 ft which I initiated then he changed that to a descent to 11000 ft which I began immediately. He also told me to expedite. He told the other aircraft to expedite to FL190. I believe the other aircraft was an air carrier flight, but I don't know the type. The air carrier called me in sight, but I never saw him. This is my best recollection of the event. I normally verify questionable clrncs with ATC, but in this case my perception was a change of rate of descent instead of altitude.

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Original NASA ASRS Text

Title: TURBOPROP CAPT MISINTERPED DSCNT CLRNC RESULTING IN OVERSHOOTING ASSIGNED INTERMEDIATE DSCNT ALT AND A CONFLICT WITH ANOTHER ACFT.

Narrative: E OF GIJ, ZAU TOLD ME TO DSND TO 13000 FT. SOMETIME DURING THE DSCNT, I WAS TOLD TO GO TO ZOB AND DID SO. AFTER CHKING IN WITH ZOB AND INFORMING HIM I WAS DSNDING TO 13000 FT, THE CTLR ASKED MY RATE OF DSCNT. I TOLD HIM IT WAS 2100 FPM AND HE TOLD ME TO 'MAINTAIN FIFTEEN.' I ANSWERED, 'ROGER, MAINTAIN FIFTEEN.' I THOUGHT HE MEANT 15000 FPM AND IT DIDN'T OCCUR TO ME THAT HE MIGHT MEAN ONE FIVE THOUSAND. I GUESS IT WAS BECAUSE HE HAD JUST ASKED MY RATE OF DSCNT AND THE USE OF FIFTEEN INSTEAD OF ONE-FIVE. I SHOULD HAVE ASKED FOR VERIFICATION. I ASSUMED THE CHANGE IN RATE OF DSCNT WAS FOR TFC AND, OF COURSE, THIS HAS OCCURRED MANY TIMES BEFORE. AT ABOUT 14200 FT, THE CTLR ASKED ME IF I RECEIVED THE ALT AND AT THIS POINT I DON'T RECALL HOW THE ALT WAS SAID AND BEFORE I COULD ANSWER HE GAVE ME A CLB TO 15000 FT WHICH I INITIATED THEN HE CHANGED THAT TO A DSCNT TO 11000 FT WHICH I BEGAN IMMEDIATELY. HE ALSO TOLD ME TO EXPEDITE. HE TOLD THE OTHER ACFT TO EXPEDITE TO FL190. I BELIEVE THE OTHER ACFT WAS AN ACR FLT, BUT I DON'T KNOW THE TYPE. THE ACR CALLED ME IN SIGHT, BUT I NEVER SAW HIM. THIS IS MY BEST RECOLLECTION OF THE EVENT. I NORMALLY VERIFY QUESTIONABLE CLRNCS WITH ATC, BUT IN THIS CASE MY PERCEPTION WAS A CHANGE OF RATE OF DSCNT INSTEAD OF ALT.

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.