Reporter followed their TCASII RA to avoid other traffic.

Attributes
ACN	465236
Time
Date	200003
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : dfw.airport
State Reference	TX
Altitude	msl bound lower : 3500 msl bound upper : 4000
Aircraft 1
Controlling Facilities	tracon : d10.tracon
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Route In Use	arrival : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : d10.tracon
Make Model Name	Widebody Transport
Flight Phase	descent : intermediate altitude
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	465236
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
ASRS Report	465287
Events
Anomaly	conflict : airborne critical non adherence : clearance other anomaly other
Independent Detector	aircraft equipment : tcas other controllera other flight crewa
Resolutory Action	controller : issued advisory controller : issued alert flight crew : returned to assigned altitude flight crew : took evasive action
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	Ambiguous

Narrative:

Upon leveling at 4000 ft and heading east while being vectored for runway 17C, we received an altitude alert on the TCASII. Shortly thereafter, approach pointed out the traffic to us. We then got a TCASII command to 'descend crossing traffic.' we began a descent and notified approach. They told us not to descend because there was traffic below us and to climb to 5000 ft. We notified them that we could not climb due to a TCASII RA. They then told us to climb back to 5000 ft as soon as we could. We did not have any traffic on TCASII below us, but did have the traffic on TCASII that we were reacting to. We felt we were in a no win position and trapped between 2 other aircraft. One we knew about on TCASII, and the other we had no idea where it was. We descended to 3500 ft and then climbed back up to altitude. As far as we know, there was no loss of separation. It was a very uncomfortable position. The controller, as soon as he saw what was happening, tried to correct the situation, but we were already well into our descent and were afraid to go against the TCASII at that point. I would stress the importance of following TCASII. I believe it kept us out of a serious situation.

Original NASA ASRS Text

Title: RPTR FOLLOWED THEIR TCASII RA TO AVOID OTHER TFC.

Narrative: UPON LEVELING AT 4000 FT AND HDG E WHILE BEING VECTORED FOR RWY 17C, WE RECEIVED AN ALT ALERT ON THE TCASII. SHORTLY THEREAFTER, APCH POINTED OUT THE TFC TO US. WE THEN GOT A TCASII COMMAND TO 'DSND XING TFC.' WE BEGAN A DSCNT AND NOTIFIED APCH. THEY TOLD US NOT TO DSND BECAUSE THERE WAS TFC BELOW US AND TO CLB TO 5000 FT. WE NOTIFIED THEM THAT WE COULD NOT CLB DUE TO A TCASII RA. THEY THEN TOLD US TO CLB BACK TO 5000 FT AS SOON AS WE COULD. WE DID NOT HAVE ANY TFC ON TCASII BELOW US, BUT DID HAVE THE TFC ON TCASII THAT WE WERE REACTING TO. WE FELT WE WERE IN A NO WIN POS AND TRAPPED BTWN 2 OTHER ACFT. ONE WE KNEW ABOUT ON TCASII, AND THE OTHER WE HAD NO IDEA WHERE IT WAS. WE DSNDED TO 3500 FT AND THEN CLBED BACK UP TO ALT. AS FAR AS WE KNOW, THERE WAS NO LOSS OF SEPARATION. IT WAS A VERY UNCOMFORTABLE POS. THE CTLR, AS SOON AS HE SAW WHAT WAS HAPPENING, TRIED TO CORRECT THE SIT, BUT WE WERE ALREADY WELL INTO OUR DSCNT AND WERE AFRAID TO GO AGAINST THE TCASII AT THAT POINT. I WOULD STRESS THE IMPORTANCE OF FOLLOWING TCASII. I BELIEVE IT KEPT US OUT OF A SERIOUS SIT.

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.