Flight crew of a canadair CL65 continued descending after observing a TCASII TA and subsequently instructed to climb after querying ARTCC controller regarding the other unknown traffic.

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Attributes
ACN	432539
Time
Date	199903
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : irq.vortac
State Reference	SC
Altitude	msl bound lower : 26000 msl bound upper : 27000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl.artcc
Operator	common carrier : air carrier
Make Model Name	Challenger CL604
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Route In Use	arrival star : sinca 3
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : ztl.artcc
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : atp
Experience	flight time last 90 days : 165 flight time total : 16000 flight time type : 400
ASRS Report	432539
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Events
Anomaly	conflict : airborne less severe non adherence : published procedure
Independent Detector	aircraft equipment : tcas other flight crewa
Resolutory Action	controller : issued new clearance
Miss Distance	horizontal : 18000 vertical : 200
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

We were cruising FL280 myr direct atl, given FL260 at irq on sinca arrival to atl. We had just turned on irq transition to sinca when we got TA on aircraft at 12-1 O'clock position indicating FL268. We were descending through FL266 when we questioned ZTL. The controller's halting reply was, 'climb and maintain FL270.' I continued my descent! When questioned again, controller said, 'maintain FL260.' no further explanation. This aircraft was apparently eastbound at FL270 and we were descended through him.

Original NASA ASRS Text

Title: FLC OF A CANADAIR CL65 CONTINUED DSNDING AFTER OBSERVING A TCASII TA AND SUBSEQUENTLY INSTRUCTED TO CLB AFTER QUERYING ARTCC CTLR REGARDING THE OTHER UNKNOWN TFC.

Narrative: WE WERE CRUISING FL280 MYR DIRECT ATL, GIVEN FL260 AT IRQ ON SINCA ARR TO ATL. WE HAD JUST TURNED ON IRQ TRANSITION TO SINCA WHEN WE GOT TA ON ACFT AT 12-1 O'CLOCK POS INDICATING FL268. WE WERE DSNDING THROUGH FL266 WHEN WE QUESTIONED ZTL. THE CTLR'S HALTING REPLY WAS, 'CLB AND MAINTAIN FL270.' I CONTINUED MY DSCNT! WHEN QUESTIONED AGAIN, CTLR SAID, 'MAINTAIN FL260.' NO FURTHER EXPLANATION. THIS ACFT WAS APPARENTLY EBOUND AT FL270 AND WE WERE DSNDED THROUGH HIM.

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.