Flight crew of an medium large transport descended in response to a TCASII RA and observation of the traffic descending toward them. ATC subsequently instructed the reporter and the other aircraft to turn and the other aircraft to stop descending and maintain their altitude.

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Attributes
ACN	341898
Time
Date	199607
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : eck
State Reference	MI
Altitude	msl bound lower : 32750 msl bound upper : 34300
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zob
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : instrument pilot : flight engineer pilot : commercial pilot : cfi
Experience	flight time last 90 days : 210 flight time total : 10000 flight time type : 400
ASRS Report	341898
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation other anomaly other
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : took evasive action other
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 12000 vertical : 1400
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

While cruising at FL330 on a direct to alb routing in the immediate vicinity of eck VOR and under the control of ZOB, I noticed traffic on our TCASII display at our 2 O'clock position descending out of FL350. Shortly after this observation we received a TCASII TA and observed the previously noticed traffic descending toward our aircraft at approximately FL346. This alert was followed immediately by a TCASII RA 'descend' advisory. At this time I assumed control of the aircraft and flew the aircraft in accordance with the commanded TCASII parameters. At this time ZOB directed us to turn 20 degrees left for traffic and directed the other aircraft (air carrier Y) to also turn 20 degrees left and to maintain their descent altitude which we observed on our TCASII to be approximately FL344. After a descent of approximately 250 ft to FL327.5 we received a 'clear of conflict' TCASII advisory. As we started our TCASII descent we notified ZOB we were descending on a TCASII RA. After 'clear of conflict' advisory we climbed back to FL330 and advised center. When I questioned ZOB on what had happened, they responded that they did not know.

Original NASA ASRS Text

Title: FLC OF AN MLG DSNDED IN RESPONSE TO A TCASII RA AND OBSERVATION OF THE TFC DSNDING TOWARD THEM. ATC SUBSEQUENTLY INSTRUCTED THE RPTR AND THE OTHER ACFT TO TURN AND THE OTHER ACFT TO STOP DSNDING AND MAINTAIN THEIR ALT.

Narrative: WHILE CRUISING AT FL330 ON A DIRECT TO ALB ROUTING IN THE IMMEDIATE VICINITY OF ECK VOR AND UNDER THE CTL OF ZOB, I NOTICED TFC ON OUR TCASII DISPLAY AT OUR 2 O'CLOCK POS DSNDING OUT OF FL350. SHORTLY AFTER THIS OBSERVATION WE RECEIVED A TCASII TA AND OBSERVED THE PREVIOUSLY NOTICED TFC DSNDING TOWARD OUR ACFT AT APPROX FL346. THIS ALERT WAS FOLLOWED IMMEDIATELY BY A TCASII RA 'DSND' ADVISORY. AT THIS TIME I ASSUMED CTL OF THE ACFT AND FLEW THE ACFT IN ACCORDANCE WITH THE COMMANDED TCASII PARAMETERS. AT THIS TIME ZOB DIRECTED US TO TURN 20 DEGS L FOR TFC AND DIRECTED THE OTHER ACFT (ACR Y) TO ALSO TURN 20 DEGS L AND TO MAINTAIN THEIR DSCNT ALT WHICH WE OBSERVED ON OUR TCASII TO BE APPROX FL344. AFTER A DSCNT OF APPROX 250 FT TO FL327.5 WE RECEIVED A 'CLR OF CONFLICT' TCASII ADVISORY. AS WE STARTED OUR TCASII DSCNT WE NOTIFIED ZOB WE WERE DSNDING ON A TCASII RA. AFTER 'CLR OF CONFLICT' ADVISORY WE CLBED BACK TO FL330 AND ADVISED CTR. WHEN I QUESTIONED ZOB ON WHAT HAD HAPPENED, THEY RESPONDED THAT THEY DID NOT KNOW.

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.