Narrative:

At 15000 ft with a frequency change for ZDC. I checked on with the controller and after my first and second 'check on' transmission we heard 'clearance delivery, descend to 11000 ft.' our call sign was 'abcd' so I called back to center 'abcd descending out of 15000 ft for 11000 ft.' when we were descending through 13500 ft, the controller queried us for our altitude. When we responded 13500 ft, he told us to climb back up to 14000 ft. We complied with his clearance and climbed back to 14000 ft. Later, we heard another aircraft with the last 2 numbers (clearance delivery) in his call sign. We assume this was the biggest reason why this happened. I figure that the other aircraft blocked my clearance readback to center for descending, therefore, center never heard my transmission that we were descending. This resulted in an altitude deviation. Supplemental information from acn 572122: he told us to maintain 14000 ft and turn left immediately to 360 degrees. He sounded excited and gave another aircraft an immediate turn also. This was our first indication that our descent from 15000 ft to 11000 ft may have been intended for another aircraft. Supplemental information from acn 572120: as we checked on with ZDC, our transmission and center's were blocked. After the second transmission, we heard a somewhat urgent request for a descent to 11000 ft for a garbled call sign that ended with 'clearance delivery' (ours was abcd). If we had accepted the wrong clearance it may have been because of the stepped on/garbled transmission or the fact of similar call signs.

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Original NASA ASRS Text

Title: B727-100 CREW DSNDED AFTER HEARING A DSCNT CLRNC CONSISTING OF ONLY THE LAST 2 NUMBERS OF THEIR CALL SIGN, AND NO COMPANY NAME.

Narrative: AT 15000 FT WITH A FREQ CHANGE FOR ZDC. I CHKED ON WITH THE CTLR AND AFTER MY FIRST AND SECOND 'CHK ON' XMISSION WE HEARD 'CD, DSND TO 11000 FT.' OUR CALL SIGN WAS 'ABCD' SO I CALLED BACK TO CTR 'ABCD DSNDING OUT OF 15000 FT FOR 11000 FT.' WHEN WE WERE DSNDING THROUGH 13500 FT, THE CTLR QUERIED US FOR OUR ALT. WHEN WE RESPONDED 13500 FT, HE TOLD US TO CLB BACK UP TO 14000 FT. WE COMPLIED WITH HIS CLRNC AND CLBED BACK TO 14000 FT. LATER, WE HEARD ANOTHER ACFT WITH THE LAST 2 NUMBERS (CD) IN HIS CALL SIGN. WE ASSUME THIS WAS THE BIGGEST REASON WHY THIS HAPPENED. I FIGURE THAT THE OTHER ACFT BLOCKED MY CLRNC READBACK TO CTR FOR DSNDING, THEREFORE, CTR NEVER HEARD MY XMISSION THAT WE WERE DSNDING. THIS RESULTED IN AN ALTDEV. SUPPLEMENTAL INFO FROM ACN 572122: HE TOLD US TO MAINTAIN 14000 FT AND TURN L IMMEDIATELY TO 360 DEGS. HE SOUNDED EXCITED AND GAVE ANOTHER ACFT AN IMMEDIATE TURN ALSO. THIS WAS OUR FIRST INDICATION THAT OUR DSCNT FROM 15000 FT TO 11000 FT MAY HAVE BEEN INTENDED FOR ANOTHER ACFT. SUPPLEMENTAL INFO FROM ACN 572120: AS WE CHKED ON WITH ZDC, OUR XMISSION AND CTR'S WERE BLOCKED. AFTER THE SECOND XMISSION, WE HEARD A SOMEWHAT URGENT REQUEST FOR A DSCNT TO 11000 FT FOR A GARBLED CALL SIGN THAT ENDED WITH 'CD' (OURS WAS ABCD). IF WE HAD ACCEPTED THE WRONG CLRNC IT MAY HAVE BEEN BECAUSE OF THE STEPPED ON/GARBLED XMISSION OR THE FACT OF SIMILAR CALL SIGNS.

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.