Air carrier CL65 flight crew reacts to TCASII alert and brings situation to the attention of ATC. ATC descends conflicting traffic, but action apparently insufficient to prevent system error.

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Attributes
ACN	411453
Time
Date	199808
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : air
State Reference	OH
Altitude	msl bound lower : 26000 msl bound upper : 26000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob
Operator	common carrier : air carrier
Make Model Name	Challenger CL604
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 205 flight time total : 14000 flight time type : 610
ASRS Report	411453
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : published procedure other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	controller : issued new clearance flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 18000 vertical : 750
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

We (X) were eastbound at FL260 on J110 from phl to cvg. Approximately 26 mi east of air we received a TA on TCASII. I observed a target at our same altitude converging at approximately 12-1 O'clock position and 20 mi. I asked center if he was talking to that traffic (Y) at our altitude and that we (X) were receiving a TCASII warning. He told us to descend to FL240. We missed the traffic (Y) by approximately '1000 ft.' fortunately our TCASII alerted us to the traffic conflict. I don't believe that center was aware of our conflict and would have flown us into each other had we not brought it to his attention.

Original NASA ASRS Text

Title: ACR CL65 FLC REACTS TO TCASII ALERT AND BRINGS SIT TO THE ATTN OF ATC. ATC DSNDS CONFLICTING TFC, BUT ACTION APPARENTLY INSUFFICIENT TO PREVENT SYS ERROR.

Narrative: WE (X) WERE EBOUND AT FL260 ON J110 FROM PHL TO CVG. APPROX 26 MI E OF AIR WE RECEIVED A TA ON TCASII. I OBSERVED A TARGET AT OUR SAME ALT CONVERGING AT APPROX 12-1 O'CLOCK POS AND 20 MI. I ASKED CTR IF HE WAS TALKING TO THAT TFC (Y) AT OUR ALT AND THAT WE (X) WERE RECEIVING A TCASII WARNING. HE TOLD US TO DSND TO FL240. WE MISSED THE TFC (Y) BY APPROX '1000 FT.' FORTUNATELY OUR TCASII ALERTED US TO THE TFC CONFLICT. I DON'T BELIEVE THAT CTR WAS AWARE OF OUR CONFLICT AND WOULD HAVE FLOWN US INTO EACH OTHER HAD WE NOT BROUGHT IT TO HIS ATTN.

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.