Narrative:

I was working radar control position at ZDC ARTCC. I had transferred radar control and communications for 1 air carrier turbojet and 1 regional turboprop to an approach control facility. The turboprop was level at 8000' and the turbojet was cleared to cross an intersection at 10000'. Both aircraft were on the same route. The turbojet descended to 8000' within close proximity to the turboprop resulting in loss of appropriate radar sep minima. Investigation of the situation found that while the original clearance issued to the turbojet was, 'turn 10 degrees left, join the south bos 1 arrival south of south bos, cross aldan at and maintain 10000',' the pilots reply was, 'turn right 10 degrees, join the arrival southeast of bos, cross aldan at 8000'.' upon request to confirm the direction of turn as left and not right, the pilot once again responded that he would cross aldan at 8000', although he corrected the direction of turn. Upon checking on frequency with approach control the pilot once again reported descending to 8000', but his first transmission was not acknowledged by the controller. The pilot called once more that he was on frequency and descending to 8000', but once again this transmission was either not heard or not understood by the controller. As the center radar controller, my evaluation of the incident is that correct altitude was issued to the pilot. He misheard or misunderstood the clearance and did the best he could to respond, although by his reply it is obvious he was confused in that he got 'left,' 'south bos,' 'south,' and '10000'' confused with other specifics. I was most immediately concerned with his direction of turn and when he repeated the wrong direction I failed to listen for other errors. The approach controller had an opportunity to correct both the pilot's and my errors, but was apparently too busy or distracted to communicate with the pilot in time. I think a major factor in this incident was the # of tasks and responsibilities required of both pilots and controllers. Pilots able to give majority of their attention to radio communications with ATC and controllers able to give exclusive auditory attention to radio frequencys might avert this sort of communications breakdown.

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Original NASA ASRS Text

Title: ACR COPIED WRONG ALT AND DESCENDED TO AN OCCUPIED ALT RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative: I WAS WORKING RADAR CTL POS AT ZDC ARTCC. I HAD TRANSFERRED RADAR CTL AND COMS FOR 1 ACR TURBOJET AND 1 REGIONAL TURBOPROP TO AN APCH CTL FAC. THE TURBOPROP WAS LEVEL AT 8000' AND THE TURBOJET WAS CLRED TO CROSS AN INTXN AT 10000'. BOTH ACFT WERE ON THE SAME RTE. THE TURBOJET DSNDED TO 8000' WITHIN CLOSE PROX TO THE TURBOPROP RESULTING IN LOSS OF APPROPRIATE RADAR SEP MINIMA. INVESTIGATION OF THE SITUATION FOUND THAT WHILE THE ORIGINAL CLRNC ISSUED TO THE TURBOJET WAS, 'TURN 10 DEGS LEFT, JOIN THE S BOS 1 ARR S OF S BOS, CROSS ALDAN AT AND MAINTAIN 10000',' THE PLTS REPLY WAS, 'TURN RIGHT 10 DEGS, JOIN THE ARR SE OF BOS, CROSS ALDAN AT 8000'.' UPON REQUEST TO CONFIRM THE DIRECTION OF TURN AS LEFT AND NOT RIGHT, THE PLT ONCE AGAIN RESPONDED THAT HE WOULD CROSS ALDAN AT 8000', ALTHOUGH HE CORRECTED THE DIRECTION OF TURN. UPON CHKING ON FREQ WITH APCH CTL THE PLT ONCE AGAIN RPTED DSNDING TO 8000', BUT HIS FIRST XMISSION WAS NOT ACKNOWLEDGED BY THE CTLR. THE PLT CALLED ONCE MORE THAT HE WAS ON FREQ AND DSNDING TO 8000', BUT ONCE AGAIN THIS XMISSION WAS EITHER NOT HEARD OR NOT UNDERSTOOD BY THE CTLR. AS THE CENTER RADAR CTLR, MY EVALUATION OF THE INCIDENT IS THAT CORRECT ALT WAS ISSUED TO THE PLT. HE MISHEARD OR MISUNDERSTOOD THE CLRNC AND DID THE BEST HE COULD TO RESPOND, ALTHOUGH BY HIS REPLY IT IS OBVIOUS HE WAS CONFUSED IN THAT HE GOT 'LEFT,' 'S BOS,' 'S,' AND '10000'' CONFUSED WITH OTHER SPECIFICS. I WAS MOST IMMEDIATELY CONCERNED WITH HIS DIRECTION OF TURN AND WHEN HE REPEATED THE WRONG DIRECTION I FAILED TO LISTEN FOR OTHER ERRORS. THE APCH CTLR HAD AN OPPORTUNITY TO CORRECT BOTH THE PLT'S AND MY ERRORS, BUT WAS APPARENTLY TOO BUSY OR DISTRACTED TO COMMUNICATE WITH THE PLT IN TIME. I THINK A MAJOR FACTOR IN THIS INCIDENT WAS THE # OF TASKS AND RESPONSIBILITIES REQUIRED OF BOTH PLTS AND CTLRS. PLTS ABLE TO GIVE MAJORITY OF THEIR ATTN TO RADIO COMS WITH ATC AND CTLRS ABLE TO GIVE EXCLUSIVE AUDITORY ATTN TO RADIO FREQS MIGHT AVERT THIS SORT OF COMS BREAKDOWN.

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.