Narrative:

Our flight (air carrier iadc) was on the acton 9 arrival to dfw, established at 11000 ft MSL and 250 KIAS. Between flato and creek intxns, we were handed off to an arrival controller who instructed us to 'turn left to 360 (and) descend and maintain 6000 ft.' clearance was acknowledged by call sign: 'air carrier iadc' and read back verbatim: 'turn left 360, departing 10000 for 6000.' the captain (flying) turned to the vector heading and initiated the descent. Passing approximately 10000 ft I observed medium large transport Y only momentarily, approaching from our 4 O'clock position, and passing right to left directly beneath our aircraft, which appeared to be within 1000 ft. When I queried the controller about medium large transport's altitude, the controller stated that he was at 9000 ft. When told that 'we had clearance to descend to 6000 ft,' he told us, 'that clearance was for an air carrier ddc.' there was a ddc on arrival to dfw, but not on the same frequency. It landed mins before us on runway 18R. The captain called the approach control supervisor and learned that a controller trnee was handling our flight and that during that period, there was a short lapse of supervision. Contributing factors: high task saturation in certain control sectors--not a good training environment for less experienced controllers. Another factor may be the similar call signs, which is a relatively new problem since companies began mixing 3 and 4 digit call signs--it seems to invite error. Callback conversation with reporter revealed the following: during a telephone call to the TRACON, reporter's captain was told that the near collision was caused by controller error. The instrument watching a trnee, turned away for a short time, and during that time, the trnee gave the descent clearance to reporter using reporter's call sign. Trnee meant to descend another aircraft, but misspoke the call sign. (Reporter stated that he had thought their altitude was 11000 ft when they started down to 6000 ft. The report showed an altitude of 10000 ft.) supplemental information from acn 90376: I initially spotted the aircraft at my 10 O'clock position, approximately distance 3 mi, converging course and steady bearing. Since we were at our assigned altitude of 10000 ft, I assumed, and it appeared, the other aircraft was at 11000 ft. I commented to my first officer, as I pointed the target out, 'I wonder why departure doesn't call him out.' the relative bearing did not change and as he got closer, my instincts, borne of a 20 yr navy background of day and night rendezvous in high performance aircraft, told me something was not right and that he was in fact at my altitude! I ordered the copilot who was at the controls: 'go down now!' he did so and avoided what could have been a midair collision as the other aircraft passed directly over us in what appeared to be a slight descent. I estimate the vertical sep, at cpa, to be 200-300 ft. Because of our extreme situation our maneuver was abrupt enough to possibly stir passenger attention. Our recovery bottomed out at 9200 ft. I estimate we may have been at 9400 ft during crossover and the other aircraft at 9700 ft. Supplemental information from acn 90440: captain called out traffic, a company large transport, at 10 O'clock, slightly high. After 5 seconds or so it became apparent we were on a constant bearing and closing. The captain called for a descent and we started down. It wasn't enough, so I rolled left and shoved the yoke over. My reflections: had we been IMC, we would not be. Had it been night, or sunset, we would not be. Had the captain been flying, and consequently a bit more committed inside the cockpit, my scan might not have picked up the large transport at about 5 mi. I've experienced closure rates like this one during air combat maneuvering in the navy, but found changing the velocity vector of a medium large transport surprisingly more difficult--something I've thought about, but not enough! Lastly, we had everything in our favor to effect a see and avoid reaction: low position, good light, a scanning pilot on the side of the threat, no autoplt to disconnect, and we still almost hit this guy.

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Original NASA ASRS Text

Title: ACR-LGT ON STAR DESCENDED THROUGH THE ALT OF ACR-MLG ON SID, RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative: OUR FLT (ACR IADC) WAS ON THE ACTON 9 ARR TO DFW, ESTABLISHED AT 11000 FT MSL AND 250 KIAS. BTWN FLATO AND CREEK INTXNS, WE WERE HANDED OFF TO AN ARR CTLR WHO INSTRUCTED US TO 'TURN L TO 360 (AND) DSND AND MAINTAIN 6000 FT.' CLRNC WAS ACKNOWLEDGED BY CALL SIGN: 'ACR IADC' AND READ BACK VERBATIM: 'TURN L 360, DEPARTING 10000 FOR 6000.' THE CAPT (FLYING) TURNED TO THE VECTOR HDG AND INITIATED THE DSCNT. PASSING APPROX 10000 FT I OBSERVED MLG Y ONLY MOMENTARILY, APCHING FROM OUR 4 O'CLOCK POS, AND PASSING R TO L DIRECTLY BENEATH OUR ACFT, WHICH APPEARED TO BE WITHIN 1000 FT. WHEN I QUERIED THE CTLR ABOUT MLG'S ALT, THE CTLR STATED THAT HE WAS AT 9000 FT. WHEN TOLD THAT 'WE HAD CLRNC TO DSND TO 6000 FT,' HE TOLD US, 'THAT CLRNC WAS FOR AN ACR DDC.' THERE WAS A DDC ON ARR TO DFW, BUT NOT ON THE SAME FREQ. IT LANDED MINS BEFORE US ON RWY 18R. THE CAPT CALLED THE APCH CTL SUPVR AND LEARNED THAT A CTLR TRNEE WAS HANDLING OUR FLT AND THAT DURING THAT PERIOD, THERE WAS A SHORT LAPSE OF SUPERVISION. CONTRIBUTING FACTORS: HIGH TASK SATURATION IN CERTAIN CTL SECTORS--NOT A GOOD TRNING ENVIRONMENT FOR LESS EXPERIENCED CTLRS. ANOTHER FACTOR MAY BE THE SIMILAR CALL SIGNS, WHICH IS A RELATIVELY NEW PROB SINCE COMPANIES BEGAN MIXING 3 AND 4 DIGIT CALL SIGNS--IT SEEMS TO INVITE ERROR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: DURING A TELEPHONE CALL TO THE TRACON, RPTR'S CAPT WAS TOLD THAT THE NEAR COLLISION WAS CAUSED BY CTLR ERROR. THE INSTR WATCHING A TRNEE, TURNED AWAY FOR A SHORT TIME, AND DURING THAT TIME, THE TRNEE GAVE THE DSCNT CLRNC TO RPTR USING RPTR'S CALL SIGN. TRNEE MEANT TO DSND ANOTHER ACFT, BUT MISSPOKE THE CALL SIGN. (RPTR STATED THAT HE HAD THOUGHT THEIR ALT WAS 11000 FT WHEN THEY STARTED DOWN TO 6000 FT. THE RPT SHOWED AN ALT OF 10000 FT.) SUPPLEMENTAL INFO FROM ACN 90376: I INITIALLY SPOTTED THE ACFT AT MY 10 O'CLOCK POS, APPROX DISTANCE 3 MI, CONVERGING COURSE AND STEADY BEARING. SINCE WE WERE AT OUR ASSIGNED ALT OF 10000 FT, I ASSUMED, AND IT APPEARED, THE OTHER ACFT WAS AT 11000 FT. I COMMENTED TO MY F/O, AS I POINTED THE TARGET OUT, 'I WONDER WHY DEP DOESN'T CALL HIM OUT.' THE RELATIVE BEARING DID NOT CHANGE AND AS HE GOT CLOSER, MY INSTINCTS, BORNE OF A 20 YR NAVY BACKGROUND OF DAY AND NIGHT RENDEZVOUS IN HIGH PERFORMANCE ACFT, TOLD ME SOMETHING WAS NOT RIGHT AND THAT HE WAS IN FACT AT MY ALT! I ORDERED THE COPLT WHO WAS AT THE CTLS: 'GO DOWN NOW!' HE DID SO AND AVOIDED WHAT COULD HAVE BEEN A MIDAIR COLLISION AS THE OTHER ACFT PASSED DIRECTLY OVER US IN WHAT APPEARED TO BE A SLIGHT DSCNT. I ESTIMATE THE VERTICAL SEP, AT CPA, TO BE 200-300 FT. BECAUSE OF OUR EXTREME SIT OUR MANEUVER WAS ABRUPT ENOUGH TO POSSIBLY STIR PAX ATTN. OUR RECOVERY BOTTOMED OUT AT 9200 FT. I ESTIMATE WE MAY HAVE BEEN AT 9400 FT DURING CROSSOVER AND THE OTHER ACFT AT 9700 FT. SUPPLEMENTAL INFO FROM ACN 90440: CAPT CALLED OUT TFC, A COMPANY LGT, AT 10 O'CLOCK, SLIGHTLY HIGH. AFTER 5 SECONDS OR SO IT BECAME APPARENT WE WERE ON A CONSTANT BEARING AND CLOSING. THE CAPT CALLED FOR A DSCNT AND WE STARTED DOWN. IT WASN'T ENOUGH, SO I ROLLED L AND SHOVED THE YOKE OVER. MY REFLECTIONS: HAD WE BEEN IMC, WE WOULD NOT BE. HAD IT BEEN NIGHT, OR SUNSET, WE WOULD NOT BE. HAD THE CAPT BEEN FLYING, AND CONSEQUENTLY A BIT MORE COMMITTED INSIDE THE COCKPIT, MY SCAN MIGHT NOT HAVE PICKED UP THE LGT AT ABOUT 5 MI. I'VE EXPERIENCED CLOSURE RATES LIKE THIS ONE DURING AIR COMBAT MANEUVERING IN THE NAVY, BUT FOUND CHANGING THE VELOCITY VECTOR OF A MLG SURPRISINGLY MORE DIFFICULT--SOMETHING I'VE THOUGHT ABOUT, BUT NOT ENOUGH! LASTLY, WE HAD EVERYTHING IN OUR FAVOR TO EFFECT A SEE AND AVOID REACTION: LOW POS, GOOD LIGHT, A SCANNING PLT ON THE SIDE OF THE THREAT, NO AUTOPLT TO DISCONNECT, AND WE STILL ALMOST HIT THIS GUY.

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.