Narrative:

Air carrier Y, a DH8 (TCASII equipped), checked on my frequency. Was approximately 20 NM northwest of aml, level at 7000 ft and was navigating direct aml, direct dca, landing dca. Air carrier X, a BE02 (non- TCASII), checked on my frequency. X was departing runway 19L at iad on a tower assigned 240 degree heading, climbing to 4000 ft. The developmental controller instructed X to turn right heading 010 degrees. I observed X northbound, approximately 5 NM southwest of aml climbing out of 6200 ft. At this time Y was 8-10 NM northwest of aml. I instructed the developmental controller to issue an immediate descent to X, an immediate climb to Y and to exchange the traffic. Y acknowledged the traffic in sight. X passed slightly west (behind Y). The radar operation at iad requires constant coordination between sectors, bwi and dca approach and ZDC. In this instance I allowed that coordination to divert my attention from the instructions the developmental controller was issuing. Due to the timely need for this coordination and the developmental controller's low hours on his first radar position I decided it would be more efficient for me to do the coordination from the overhead position, pass the instructions to the developmental, and then explain the process in detail during our training debrief. Supplemental information from acn 270622: after departing runway 19 at iad, air carrier X began the SID, which called for flying runway heading and climbing to 4000 ft. After contacting iad departure we were assigned a southwest heading of approximately 240 degrees. Shortly after, we were assigned a north heading of approximately 010 degrees and told to climb and maintain 7000 ft. Just as we reached our assigned altitude of 7000 ft iad departure told us to make an immediate descent to 6000 ft due to traffic in our 12 O'clock position, also at 7000 ft. As we were about to initiate the descent both my first officer and myself saw the traffic. It was a dash 8 ahead and slightly to our left. The dash 8 was crossing from our left to right and appeared to be descending. We started a left turn and did not begin our descent until the dash 8 had passed. Descending immediately would have decreased the separation if not caused a collision. After the dash 8 passed we descended as instructed to 6000 ft. At the time our courses crossed, I estimate we were approximately 150 ft above the dash 8. We also were slightly behind the dash 8, possibly 1/4 mi or less. Shortly after passing the dash 8, ATC told us it was an operational error on their part and it would be looked into.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR X CLB TO OCCUPIED ALT HAD LTSS FROM ACR Y. SYS ERROR.

Narrative: ACR Y, A DH8 (TCASII EQUIPPED), CHKED ON MY FREQ. WAS APPROX 20 NM NW OF AML, LEVEL AT 7000 FT AND WAS NAVING DIRECT AML, DIRECT DCA, LNDG DCA. ACR X, A BE02 (NON- TCASII), CHKED ON MY FREQ. X WAS DEPARTING RWY 19L AT IAD ON A TWR ASSIGNED 240 DEG HDG, CLBING TO 4000 FT. THE DEVELOPMENTAL CTLR INSTRUCTED X TO TURN R HDG 010 DEGS. I OBSERVED X NBOUND, APPROX 5 NM SW OF AML CLBING OUT OF 6200 FT. AT THIS TIME Y WAS 8-10 NM NW OF AML. I INSTRUCTED THE DEVELOPMENTAL CTLR TO ISSUE AN IMMEDIATE DSCNT TO X, AN IMMEDIATE CLB TO Y AND TO EXCHANGE THE TFC. Y ACKNOWLEDGED THE TFC IN SIGHT. X PASSED SLIGHTLY W (BEHIND Y). THE RADAR OP AT IAD REQUIRES CONSTANT COORD BTWN SECTORS, BWI AND DCA APCH AND ZDC. IN THIS INSTANCE I ALLOWED THAT COORD TO DIVERT MY ATTN FROM THE INSTRUCTIONS THE DEVELOPMENTAL CTLR WAS ISSUING. DUE TO THE TIMELY NEED FOR THIS COORD AND THE DEVELOPMENTAL CTLR'S LOW HRS ON HIS FIRST RADAR POS I DECIDED IT WOULD BE MORE EFFICIENT FOR ME TO DO THE COORD FROM THE OVERHEAD POS, PASS THE INSTRUCTIONS TO THE DEVELOPMENTAL, AND THEN EXPLAIN THE PROCESS IN DETAIL DURING OUR TRAINING DEBRIEF. SUPPLEMENTAL INFO FROM ACN 270622: AFTER DEPARTING RWY 19 AT IAD, ACR X BEGAN THE SID, WHICH CALLED FOR FLYING RWY HDG AND CLBING TO 4000 FT. AFTER CONTACTING IAD DEP WE WERE ASSIGNED A SW HDG OF APPROX 240 DEGS. SHORTLY AFTER, WE WERE ASSIGNED A N HDG OF APPROX 010 DEGS AND TOLD TO CLB AND MAINTAIN 7000 FT. JUST AS WE REACHED OUR ASSIGNED ALT OF 7000 FT IAD DEP TOLD US TO MAKE AN IMMEDIATE DSCNT TO 6000 FT DUE TO TFC IN OUR 12 O'CLOCK POS, ALSO AT 7000 FT. AS WE WERE ABOUT TO INITIATE THE DSCNT BOTH MY FO AND MYSELF SAW THE TFC. IT WAS A DASH 8 AHEAD AND SLIGHTLY TO OUR L. THE DASH 8 WAS XING FROM OUR L TO R AND APPEARED TO BE DSNDING. WE STARTED A L TURN AND DID NOT BEGIN OUR DSCNT UNTIL THE DASH 8 HAD PASSED. DSNDING IMMEDIATELY WOULD HAVE DECREASED THE SEPARATION IF NOT CAUSED A COLLISION. AFTER THE DASH 8 PASSED WE DSNDED AS INSTRUCTED TO 6000 FT. AT THE TIME OUR COURSES CROSSED, I ESTIMATE WE WERE APPROX 150 FT ABOVE THE DASH 8. WE ALSO WERE SLIGHTLY BEHIND THE DASH 8, POSSIBLY 1/4 MI OR LESS. SHORTLY AFTER PASSING THE DASH 8, ATC TOLD US IT WAS AN OPERROR ON THEIR PART AND IT WOULD BE LOOKED INTO.

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.