Narrative:

I was flying and the captain was talking to ATC. We were clrd to 4000' by approach control and slow to 170 KTS at 4000'. The problem first began when, before reaching 4000', I heard a clearance to 1700'. I was not sure who it was for because I had missed the call sign. But, I distinctly heard the captain read back our call sign and clrd to 1700' leaving 5000'. The controller responded, 'roger.' I remember listening for the controller's response because I did have a question about the clearance. My doubt was gone. A second readback of 1700' clrd altitude took place when the controller again asked us to slow to 170 KTS. Captain said, 'roger, slow to 170 KTS then down to 1700'.' just before we leveled at 1700' the controller said to us, 'check your altitude.' captain said leveling 1700' and I read back 1700'. Controller said, '1700' altitude was for another aircraft, but you can stay at 1700'.' to prevent this from happening again, anytime I have any doubt about a clearance I will use the word confirm in my readback to increase the controller's attention to my readback. Supplemental information from acn 80109: passing 5000' I thought I heard, 'company xay, des to 1700.' I read back, 'company xay descending to 1700', leaving 5000'.' as we approached 4000' the controller said, 'company xay slow to 170 KTS at 4000'.' I replied, 'roger, slow to 170 KTS at 4000', descending to 1700', company xay.' no response was heard. At about 2400', the controller said, 'company xay, check altitude.' I replied, 'leaving 3 for 1700', I previously read back my clearance to 1700'.' the controller responded, 'roger, des now to 1700', that clearance was for air carrier B xby.' the copilot, who was flying the large transport, told me that there was some question in his mind about the clearance, but all doubt was removed when I read back the clearance a second time. Perhaps if the first officer voiced his doubts the first time it could have been clarified. I do feel the controller should have caught the discrepancy on one of my readbacks.

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Original NASA ASRS Text

Title: ACR LGT DESCENDED THROUGH ASSIGNED ALT AFTER READING BACK INCORRECT LOWER ALT WITHOUT ATC CORRECTION.

Narrative: I WAS FLYING AND THE CAPT WAS TALKING TO ATC. WE WERE CLRD TO 4000' BY APCH CTL AND SLOW TO 170 KTS AT 4000'. THE PROB FIRST BEGAN WHEN, BEFORE REACHING 4000', I HEARD A CLRNC TO 1700'. I WAS NOT SURE WHO IT WAS FOR BECAUSE I HAD MISSED THE CALL SIGN. BUT, I DISTINCTLY HEARD THE CAPT READ BACK OUR CALL SIGN AND CLRD TO 1700' LEAVING 5000'. THE CTLR RESPONDED, 'ROGER.' I REMEMBER LISTENING FOR THE CTLR'S RESPONSE BECAUSE I DID HAVE A QUESTION ABOUT THE CLRNC. MY DOUBT WAS GONE. A SECOND READBACK OF 1700' CLRD ALT TOOK PLACE WHEN THE CTLR AGAIN ASKED US TO SLOW TO 170 KTS. CAPT SAID, 'ROGER, SLOW TO 170 KTS THEN DOWN TO 1700'.' JUST BEFORE WE LEVELED AT 1700' THE CTLR SAID TO US, 'CHK YOUR ALT.' CAPT SAID LEVELING 1700' AND I READ BACK 1700'. CTLR SAID, '1700' ALT WAS FOR ANOTHER ACFT, BUT YOU CAN STAY AT 1700'.' TO PREVENT THIS FROM HAPPENING AGAIN, ANYTIME I HAVE ANY DOUBT ABOUT A CLRNC I WILL USE THE WORD CONFIRM IN MY READBACK TO INCREASE THE CTLR'S ATTN TO MY READBACK. SUPPLEMENTAL INFORMATION FROM ACN 80109: PASSING 5000' I THOUGHT I HEARD, 'COMPANY XAY, DES TO 1700.' I READ BACK, 'COMPANY XAY DSNDING TO 1700', LEAVING 5000'.' AS WE APCHED 4000' THE CTLR SAID, 'COMPANY XAY SLOW TO 170 KTS AT 4000'.' I REPLIED, 'ROGER, SLOW TO 170 KTS AT 4000', DSNDING TO 1700', COMPANY XAY.' NO RESPONSE WAS HEARD. AT ABOUT 2400', THE CTLR SAID, 'COMPANY XAY, CHK ALT.' I REPLIED, 'LEAVING 3 FOR 1700', I PREVIOUSLY READ BACK MY CLRNC TO 1700'.' THE CTLR RESPONDED, 'ROGER, DES NOW TO 1700', THAT CLRNC WAS FOR ACR B XBY.' THE COPLT, WHO WAS FLYING THE LGT, TOLD ME THAT THERE WAS SOME QUESTION IN HIS MIND ABOUT THE CLRNC, BUT ALL DOUBT WAS REMOVED WHEN I READ BACK THE CLRNC A SECOND TIME. PERHAPS IF THE F/O VOICED HIS DOUBTS THE FIRST TIME IT COULD HAVE BEEN CLARIFIED. I DO FEEL THE CTLR SHOULD HAVE CAUGHT THE DISCREPANCY ON ONE OF MY READBACKS.

Data retrieved from NASA's ASRS site as of August 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.