Narrative:

The planes involved air carrier X, an medium large transport, dal btr A5 msy at FL330, and air carrier Y, an medium large transport, pbi mcb aex S5 dfw at FL310. Air carrier X was given descent to FL240 with pilot discretion out of FL370. After a min or so, I noticed that air carrier Y and air carrier X were going to be tight. So, I turned air carrier X to a heading of 090 degrees. I then tried to turn air carrier Y. No answer. So, I tried again and it was at this time air carrier Y told me he was responding to a TCASII advisory and that they were descending. I told air carrier Y to maintain FL310 and fly heading 220 degrees. It took a total of 36 seconds from first transmission until he rogered turn. TCASII did not cause this error, but it enhanced it greatly. Air carrier Y descended 1400 ft because the crew later stated that their TCASII showed someone climbing at them. If anything, air carrier Y's TCASII should have told the crew to climb. With TCASII the separation was 500 ft and 2 1/2 mi. With no TCASII action it should have been 1900 ft and 2 1/2 mi. Supplemental information from acn 258001: we were flying at FL310 (level) 30 DME east of aex on J-50 when we got a TCASII alert at 12 O'clock. A few seconds later, we got an RA commanding a 2500 FPM descent. We began our descent and notified ATC. At this time, ZHU told us to maintain FL310 and turn to heading 220 degrees (about a 70 degree left turn). The TCASII was still saying descend, so we kept descending and turned to 220 degrees. At about 29500 ft, I saw the other plane below us and to the right. We then stopped our descent and climbed back to FL310. ZHU never questioned us about leaving FL310 and soon told us to fly direct aex. I then asked them what happened and all they said was another plane (air carrier X, I think) was descending from FL330 to FL290. They said they would note that we departed our assigned altitude because of a TCASII RA.

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Original NASA ASRS Text

Title: ACR IN DSCNT HAS A CONFLICT WITH ANOTHER ACR RESULTING IN LTSS.

Narrative: THE PLANES INVOLVED ACR X, AN MLG, DAL BTR A5 MSY AT FL330, AND ACR Y, AN MLG, PBI MCB AEX S5 DFW AT FL310. ACR X WAS GIVEN DSCNT TO FL240 WITH PLT DISCRETION OUT OF FL370. AFTER A MIN OR SO, I NOTICED THAT ACR Y AND ACR X WERE GOING TO BE TIGHT. SO, I TURNED ACR X TO A HDG OF 090 DEGS. I THEN TRIED TO TURN ACR Y. NO ANSWER. SO, I TRIED AGAIN AND IT WAS AT THIS TIME ACR Y TOLD ME HE WAS RESPONDING TO A TCASII ADVISORY AND THAT THEY WERE DSNDING. I TOLD ACR Y TO MAINTAIN FL310 AND FLY HDG 220 DEGS. IT TOOK A TOTAL OF 36 SECONDS FROM FIRST XMISSION UNTIL HE ROGERED TURN. TCASII DID NOT CAUSE THIS ERROR, BUT IT ENHANCED IT GREATLY. ACR Y DSNDED 1400 FT BECAUSE THE CREW LATER STATED THAT THEIR TCASII SHOWED SOMEONE CLBING AT THEM. IF ANYTHING, ACR Y'S TCASII SHOULD HAVE TOLD THE CREW TO CLB. WITH TCASII THE SEPARATION WAS 500 FT AND 2 1/2 MI. WITH NO TCASII ACTION IT SHOULD HAVE BEEN 1900 FT AND 2 1/2 MI. SUPPLEMENTAL INFO FROM ACN 258001: WE WERE FLYING AT FL310 (LEVEL) 30 DME E OF AEX ON J-50 WHEN WE GOT A TCASII ALERT AT 12 O'CLOCK. A FEW SECONDS LATER, WE GOT AN RA COMMANDING A 2500 FPM DSCNT. WE BEGAN OUR DSCNT AND NOTIFIED ATC. AT THIS TIME, ZHU TOLD US TO MAINTAIN FL310 AND TURN TO HDG 220 DEGS (ABOUT A 70 DEG L TURN). THE TCASII WAS STILL SAYING DSND, SO WE KEPT DSNDING AND TURNED TO 220 DEGS. AT ABOUT 29500 FT, I SAW THE OTHER PLANE BELOW US AND TO THE R. WE THEN STOPPED OUR DSCNT AND CLBED BACK TO FL310. ZHU NEVER QUESTIONED US ABOUT LEAVING FL310 AND SOON TOLD US TO FLY DIRECT AEX. I THEN ASKED THEM WHAT HAPPENED AND ALL THEY SAID WAS ANOTHER PLANE (ACR X, I THINK) WAS DSNDING FROM FL330 TO FL290. THEY SAID THEY WOULD NOTE THAT WE DEPARTED OUR ASSIGNED ALT BECAUSE OF A TCASII RA.

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.