Narrative:

During cruise at FL370, descent clearance was issued to cross 25 DME northeast of gve VORTAC at FL290. (We were on the dupont 3 arrival to phl). Our position was about 40 southeast of gve, so we began the descent immediately. While passing over gve at FL300, the controller told us to cross 10 DME northeast at FL290. We queried the controller to verify the original clearance and complied with the last issued. The controller then told us to turn to 180 degree heading (we were leveling at FL290 then) and did not answer our question of verifying the original clearance. We asked 2 more times and never did get an answer. While going through FL300, we saw an aircraft pass off to our left, of really no factor, but probably too close for ATC sep. Upon checking the next day with the dca FAA, I learned we had been in conflict vertically by 1600' and horizontally by 4 mi. Our original clearance was correct as we were doing it but the controller had misjudged slightly and then offered no explanation. In my judgement, we were in no danger at any time, however, minimum clearance fot the attitude was encroached upon due to controller error.

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Original NASA ASRS Text

Title: ACR ACFT RECEIVES AMENDED CLRNC TOO LATE TO AVOID LESS THAN STANDARD SEPARATION.

Narrative: DURING CRUISE AT FL370, DSNT CLRNC WAS ISSUED TO CROSS 25 DME NE OF GVE VORTAC AT FL290. (WE WERE ON THE DUPONT 3 ARR TO PHL). OUR POS WAS ABOUT 40 SE OF GVE, SO WE BEGAN THE DSNT IMMEDIATELY. WHILE PASSING OVER GVE AT FL300, THE CTLR TOLD US TO CROSS 10 DME NE AT FL290. WE QUERIED THE CTLR TO VERIFY THE ORIGINAL CLRNC AND COMPLIED WITH THE LAST ISSUED. THE CTLR THEN TOLD US TO TURN TO 180 DEG HDG (WE WERE LEVELING AT FL290 THEN) AND DID NOT ANSWER OUR QUESTION OF VERIFYING THE ORIGINAL CLRNC. WE ASKED 2 MORE TIMES AND NEVER DID GET AN ANSWER. WHILE GOING THROUGH FL300, WE SAW AN ACFT PASS OFF TO OUR L, OF REALLY NO FACTOR, BUT PROBABLY TOO CLOSE FOR ATC SEP. UPON CHKING THE NEXT DAY WITH THE DCA FAA, I LEARNED WE HAD BEEN IN CONFLICT VERTICALLY BY 1600' AND HORIZLY BY 4 MI. OUR ORIGINAL CLRNC WAS CORRECT AS WE WERE DOING IT BUT THE CTLR HAD MISJUDGED SLIGHTLY AND THEN OFFERED NO EXPLANATION. IN MY JUDGEMENT, WE WERE IN NO DANGER AT ANY TIME, HOWEVER, MINIMUM CLRNC FOT THE ATTITUDE WAS ENCROACHED UPON DUE TO CTLR ERROR.

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.