Less than standard separation between 2 air carrier. Operational error.

Attributes
ACN	96742
Time
Date	198810
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : adm
State Reference	OK
Altitude	msl bound lower : 23800 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Route In Use	arrival star : star enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude descent other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 3500 flight time type : 600
ASRS Report	96742
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 6500 flight time type : 2300
ASRS Report	96062
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	other other : unspecified atc
Resolutory Action	controller : issued new clearance flight crew : took evasive action none taken : unable
Consequence	faa : investigated faa : reviewed incident with flight crew
Miss Distance	horizontal : 11400 vertical : 200
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

We, air carrier X, were inbound to dfw. We had just passed ardmore VOR southbound when directed to descend from FL280 to FL240 and maintain 280 KTS IAS. We acknowledged the transmission and proceeded as cleared. After we leveled at FL240 we received a transmission to turn immediately 90 degrees right, and we did so. After we acknowledged the command we heard air carrier Y say he had us in sight and was also turning. After the controller spoke with air carrier Y he came back to us, air carrier X, and advised us we were to be at FL250 and not FL240. We responded by stating we had received clearance to descend to FL240 and maintain 250 KTS. Air carrier Y said this was too close and we needed to discuss this further. We, X crew, never had Y in sight and his direction was unknown to us. Position and direction of X was FL240, 280 KIAS, 198 degree right adm/bpr 018 degree right, correct altitude for direction being flown. After the incident air carrier Y received clearance to descend to FL230. Supplemental information from acn 96297: shortly after reaching FL240 controller urgently reclred us, air carrier Y to FL230. At our 10 O'clock position was air carrier X at same altitude in a sharp right turn. Estimated distance 2 mi or less at same altitude. The snitch computer program had alerted controller to conflict at the time the other aircraft was in a blind spot to me due to windshield post.

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN 2 ACR. OPERATIONAL ERROR.

Narrative: WE, ACR X, WERE INBND TO DFW. WE HAD JUST PASSED ARDMORE VOR SBND WHEN DIRECTED TO DSND FROM FL280 TO FL240 AND MAINTAIN 280 KTS IAS. WE ACKNOWLEDGED THE XMISSION AND PROCEEDED AS CLRED. AFTER WE LEVELED AT FL240 WE RECEIVED A XMISSION TO TURN IMMEDIATELY 90 DEGS RIGHT, AND WE DID SO. AFTER WE ACKNOWLEDGED THE COMMAND WE HEARD ACR Y SAY HE HAD US IN SIGHT AND WAS ALSO TURNING. AFTER THE CTLR SPOKE WITH ACR Y HE CAME BACK TO US, ACR X, AND ADVISED US WE WERE TO BE AT FL250 AND NOT FL240. WE RESPONDED BY STATING WE HAD RECEIVED CLRNC TO DSND TO FL240 AND MAINTAIN 250 KTS. ACR Y SAID THIS WAS TOO CLOSE AND WE NEEDED TO DISCUSS THIS FURTHER. WE, X CREW, NEVER HAD Y IN SIGHT AND HIS DIRECTION WAS UNKNOWN TO US. POS AND DIRECTION OF X WAS FL240, 280 KIAS, 198 DEG R ADM/BPR 018 DEG R, CORRECT ALT FOR DIRECTION BEING FLOWN. AFTER THE INCIDENT ACR Y RECEIVED CLRNC TO DSND TO FL230. SUPPLEMENTAL INFO FROM ACN 96297: SHORTLY AFTER REACHING FL240 CTLR URGENTLY RECLRED US, ACR Y TO FL230. AT OUR 10 O'CLOCK POS WAS ACR X AT SAME ALT IN A SHARP RIGHT TURN. ESTIMATED DISTANCE 2 MI OR LESS AT SAME ALT. THE SNITCH COMPUTER PROGRAM HAD ALERTED CTLR TO CONFLICT AT THE TIME THE OTHER ACFT WAS IN A BLIND SPOT TO ME DUE TO WINDSHIELD POST.

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.