Narrative:

I was assigned sector 26 on a XA00-XI00 shift. After taking a break I relieved the sector 27 radar controller at about XC40 am. Light transport X (abc ab) was en route to dca via seg balance dca at FL180. Small transport Y (xyz ab) was entre to phl via har lrp V210 bucks phl, descending to 110. Large transport Z was also en route to phl. I decided to let large transport Z be first over lrp. To accomplish this I stopped small transport Y (xyz ab's) descent at FL190 and turned him to a 070 degree heading to go behind large transport Z. I stopped small transport Y (xyz ab) at FL190 to go over light transport X (abc ab) since I had turned small transport Y (xyz ab) towards light transport X (abc ab). I then cleared light transport X (abc ab) to descend to 130, as required by area policy. However small transport Y (xyz ab) because of similarity of call signs mistakenly took the descent clearance and I missed his readback. When I noticed small transport Y (xyz ab's) mode C readout at FL187, I asked him to verify level at FL190. The pilot replied, 'negative, I have been cleared to descend to 130.' I then replied 'negative, you were cleared to maintain FL190.' small transport Y (xyz ab) then, after going as low as FL184, climbed back to FL190, however, he was already within 5 mi of light transport X. I believe light transport X was having problems with his radio because he did not respond to my next three control instructions, the first of which was to descend. Human performance considerations include small transport Y (xyz ab) pilot perception of expecting lower altitude and my own belief in hearing what I perceived and not what was really said. Also my working to let large transport Z be first instead of second which would have been easier.

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Original NASA ASRS Text

Title: CPR SMT TOOK THE DESCENT CLRNC MEANT FOR CPR LTT AND THE CTLR MISSED THE ERROR IN READBACK. LESS THAN STANDARD SEPARATION BETWEEN THESE TWO ACFT.

Narrative: I WAS ASSIGNED SECTOR 26 ON A XA00-XI00 SHIFT. AFTER TAKING A BREAK I RELIEVED THE SECTOR 27 RADAR CTLR AT ABOUT XC40 AM. LTT X (ABC AB) WAS ENRTE TO DCA VIA SEG BAL DCA AT FL180. SMT Y (XYZ AB) WAS ENTRE TO PHL VIA HAR LRP V210 BUCKS PHL, DSNDING TO 110. LGT Z WAS ALSO ENRTE TO PHL. I DECIDED TO LET LGT Z BE FIRST OVER LRP. TO ACCOMPLISH THIS I STOPPED SMT Y (XYZ AB'S) DSCNT AT FL190 AND TURNED HIM TO A 070 DEG HEADING TO GO BEHIND LGT Z. I STOPPED SMT Y (XYZ AB) AT FL190 TO GO OVER LTT X (ABC AB) SINCE I HAD TURNED SMT Y (XYZ AB) TOWARDS LTT X (ABC AB). I THEN CLRED LTT X (ABC AB) TO DSND TO 130, AS REQUIRED BY AREA POLICY. HOWEVER SMT Y (XYZ AB) BECAUSE OF SIMILARITY OF CALL SIGNS MISTAKENLY TOOK THE DSCNT CLRNC AND I MISSED HIS READBACK. WHEN I NOTICED SMT Y (XYZ AB'S) MODE C READOUT AT FL187, I ASKED HIM TO VERIFY LEVEL AT FL190. THE PLT REPLIED, 'NEGATIVE, I HAVE BEEN CLRED TO DSND TO 130.' I THEN REPLIED 'NEGATIVE, YOU WERE CLRED TO MAINTAIN FL190.' SMT Y (XYZ AB) THEN, AFTER GOING AS LOW AS FL184, CLBED BACK TO FL190, HOWEVER, HE WAS ALREADY WITHIN 5 MI OF LTT X. I BELIEVE LTT X WAS HAVING PROBLEMS WITH HIS RADIO BECAUSE HE DID NOT RESPOND TO MY NEXT THREE CONTROL INSTRUCTIONS, THE FIRST OF WHICH WAS TO DSND. HUMAN PERFORMANCE CONSIDERATIONS INCLUDE SMT Y (XYZ AB) PLT PERCEPTION OF EXPECTING LOWER ALT AND MY OWN BELIEF IN HEARING WHAT I PERCEIVED AND NOT WHAT WAS REALLY SAID. ALSO MY WORKING TO LET LGT Z BE FIRST INSTEAD OF SECOND WHICH WOULD HAVE BEEN EASIER.

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.