Narrative:

During the course of the descent I noted on our TCASII display an aircraft, that due to his relative altitude and movement, to be eastbound at 4000 ft approximately 2 1/2-3 mi ahead of us, at our 1 O'clock position. Descending through 4200 ft approach turned us to a 180 heading, which we did while leveling at 4000 ft. During our descent and turn, approach gave the other aircraft, which I believe was an light transport Y, several clrncs. First to turn to a 180 heading, shortly thereafter to tighten up his turn, then to increase his speed to 200 KTS, then to turn to 250 degrees. After leveling off at 4000 ft and completing our turn to south, I looked at the TCASII display and noted what I believe was the other aircraft within 1 mi of us, at our altitude. The TCASII symbol for this aircraft had turned to a solid blue diamond, indicating a possible conflict. Several seconds later the symbol turned into a red DOT and the TCASII commanded a descent, both on the display and verbally. I immediately complied, reducing the power to idle and pushing the nose down firmly. The TCASII gave us a clear of conflict report passing 3700 ft. We never received a TA report from the TCASII or approach. About that time approach asked us what our flight conditions were, which I believe was to find out if we were in VMC conditions and could see the other aircraft to provide our own separation. We replied that were in IMC conditions. We then climbed back up to 4000 ft and continued to ord for a normal approach and landing. Factors contributing to this situation were volume of traffic -- it was very busy. It appears as if the other flight may have been slow to comply with his clearance or turned with a slow rate of turn. The controller had us descend from 7000 ft to 4000 ft with a min or less than min horizontal spacing between us and the other aircraft. It also appeared to me that the controller was getting tired. He was very curt with us and several other pilots on the frequency. I don't know if we would have collided with the TCASII, but we would have come a lot closer to each other without it.

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Original NASA ASRS Text

Title: POTENTIAL CONFLICT ENSUES WITH AN ALTDEV ALT EXCURSION CREATED BY TCASII RA AND FOLLOWING PLT RESPONSE.

Narrative: DURING THE COURSE OF THE DSCNT I NOTED ON OUR TCASII DISPLAY AN ACFT, THAT DUE TO HIS RELATIVE ALT AND MOVEMENT, TO BE EBOUND AT 4000 FT APPROX 2 1/2-3 MI AHEAD OF US, AT OUR 1 O'CLOCK POS. DSNDING THROUGH 4200 FT APCH TURNED US TO A 180 HDG, WHICH WE DID WHILE LEVELING AT 4000 FT. DURING OUR DSCNT AND TURN, APCH GAVE THE OTHER ACFT, WHICH I BELIEVE WAS AN LTT Y, SEVERAL CLRNCS. FIRST TO TURN TO A 180 HDG, SHORTLY THEREAFTER TO TIGHTEN UP HIS TURN, THEN TO INCREASE HIS SPD TO 200 KTS, THEN TO TURN TO 250 DEGS. AFTER LEVELING OFF AT 4000 FT AND COMPLETING OUR TURN TO S, I LOOKED AT THE TCASII DISPLAY AND NOTED WHAT I BELIEVE WAS THE OTHER ACFT WITHIN 1 MI OF US, AT OUR ALT. THE TCASII SYMBOL FOR THIS ACFT HAD TURNED TO A SOLID BLUE DIAMOND, INDICATING A POSSIBLE CONFLICT. SEVERAL SECONDS LATER THE SYMBOL TURNED INTO A RED DOT AND THE TCASII COMMANDED A DSCNT, BOTH ON THE DISPLAY AND VERBALLY. I IMMEDIATELY COMPLIED, REDUCING THE PWR TO IDLE AND PUSHING THE NOSE DOWN FIRMLY. THE TCASII GAVE US A CLR OF CONFLICT RPT PASSING 3700 FT. WE NEVER RECEIVED A TA RPT FROM THE TCASII OR APCH. ABOUT THAT TIME APCH ASKED US WHAT OUR FLT CONDITIONS WERE, WHICH I BELIEVE WAS TO FIND OUT IF WE WERE IN VMC CONDITIONS AND COULD SEE THE OTHER ACFT TO PROVIDE OUR OWN SEPARATION. WE REPLIED THAT WERE IN IMC CONDITIONS. WE THEN CLBED BACK UP TO 4000 FT AND CONTINUED TO ORD FOR A NORMAL APCH AND LNDG. FACTORS CONTRIBUTING TO THIS SITUATION WERE VOLUME OF TFC -- IT WAS VERY BUSY. IT APPEARS AS IF THE OTHER FLT MAY HAVE BEEN SLOW TO COMPLY WITH HIS CLRNC OR TURNED WITH A SLOW RATE OF TURN. THE CTLR HAD US DSND FROM 7000 FT TO 4000 FT WITH A MIN OR LESS THAN MIN HORIZ SPACING BTWN US AND THE OTHER ACFT. IT ALSO APPEARED TO ME THAT THE CTLR WAS GETTING TIRED. HE WAS VERY CURT WITH US AND SEVERAL OTHER PLTS ON THE FREQ. I DON'T KNOW IF WE WOULD HAVE COLLIDED WITH THE TCASII, BUT WE WOULD HAVE COME A LOT CLOSER TO EACH OTHER WITHOUT IT.

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.