Narrative:

Air carrier X during level flight, on the autoplt tracking direct to the fwa VOR at FL280, ATC suddenly instructed us to make a tight left turn of approximately 90 degrees. It was obviously due to a traffic conflict so while the first officer began a turn to the left on the autoplt, I asked ATC for a confirmation. At the same time our TCASII gave us a TA, and the target was 12 O'clock above us and descending. Immediately after that a descend RA was generated by TCASII and commanded a 2000 plus FPM dive. This was the first RA the first officer had ever seen so he was a little slow to get the airplane started down. TCASII generated an 'increase descent' RA so I grabbed the controls, disengaged the autoplt, deployed half speed brakes and got the vsi needle at or below the green band on the vertical speed indicator. When the descend RA was first given I scaled the TCASII screen down to the 5 mi scale so for a moment the intruding aircraft was not on the screen. While all this was happening the ATC controller was issuing a lot of hurried instructions and one of them I thought was for our intruding aircraft to descend to FL270. When the aircraft re- appeared on our TCASII screen, it was slightly left of our 12 O'clock position opposite direction and closing fast, at FL274 and descending. We were passing through FL270 descending and turning into it as instructed by ATC. I acquired the aircraft visually less than a mi away and had just enough time to roll the aircraft back to the right before passing less than 100 yds laterally and around 500 vertically. I believe we got down to 26500 ft although the flight engineer thought it was 25500 ft. When I advised ATC of our altitude, he was alarmed and wanted to know why we were not at FL280. I advised him of our TCASII 'RA' and after asking what altitude he wanted us to return to, he said FL270 and no other comments were made. I'm a firm believer in TCASII. If you follow it, it will keep you clear of the intruding aircraft. It's real hard to suddenly punch off the autoplt and deviate from your assigned altitude without a clearance but there is really no other way to do it. If you wind up diving down on another aircraft you have to trust that TCASII will keep you clear but only if everybody follows their TCASII instructions, I suspect that we had to deviate so far from our assigned altitude was because the intruding aircraft either did not have TCASII on board or that the crew of the other aircraft followed ATC's instructions to descend to FL270 rather than following their TCASII which should have been instructing them to shallow their descent or even climb. Callback conversation with reporter revealed the following information: reporter stated the controller did not issue traffic or the reason for the radar vector off course. TCASII was reduced from 40 mi range to 5 mi range. Reporter stated no advisory was given to ATC that they were responding to an RA until after the incident. Flight crew ATC review facility supervisor said an operational error was being filed. Reporter did not know if air carrier CL60 had TCASII or responded to TCASII.

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Original NASA ASRS Text

Title: ACR X TCASII TA RA HAD NMAC LTSS FROM ACR CL60. EVASIVE ACTION DSND. SYS ERROR.

Narrative: ACR X DURING LEVEL FLT, ON THE AUTOPLT TRACKING DIRECT TO THE FWA VOR AT FL280, ATC SUDDENLY INSTRUCTED US TO MAKE A TIGHT L TURN OF APPROX 90 DEGS. IT WAS OBVIOUSLY DUE TO A TFC CONFLICT SO WHILE THE FO BEGAN A TURN TO THE L ON THE AUTOPLT, I ASKED ATC FOR A CONFIRMATION. AT THE SAME TIME OUR TCASII GAVE US A TA, AND THE TARGET WAS 12 O'CLOCK ABOVE US AND DSNDING. IMMEDIATELY AFTER THAT A DSND RA WAS GENERATED BY TCASII AND COMMANDED A 2000 PLUS FPM DIVE. THIS WAS THE FIRST RA THE FO HAD EVER SEEN SO HE WAS A LITTLE SLOW TO GET THE AIRPLANE STARTED DOWN. TCASII GENERATED AN 'INCREASE DSCNT' RA SO I GRABBED THE CTLS, DISENGAGED THE AUTOPLT, DEPLOYED HALF SPD BRAKES AND GOT THE VSI NEEDLE AT OR BELOW THE GREEN BAND ON THE VERT SPD INDICATOR. WHEN THE DSND RA WAS FIRST GIVEN I SCALED THE TCASII SCREEN DOWN TO THE 5 MI SCALE SO FOR A MOMENT THE INTRUDING ACFT WAS NOT ON THE SCREEN. WHILE ALL THIS WAS HAPPENING THE ATC CTLR WAS ISSUING A LOT OF HURRIED INSTRUCTIONS AND ONE OF THEM I THOUGHT WAS FOR OUR INTRUDING ACFT TO DSND TO FL270. WHEN THE ACFT RE- APPEARED ON OUR TCASII SCREEN, IT WAS SLIGHTLY L OF OUR 12 O'CLOCK POS OPPOSITE DIRECTION AND CLOSING FAST, AT FL274 AND DSNDING. WE WERE PASSING THROUGH FL270 DSNDING AND TURNING INTO IT AS INSTRUCTED BY ATC. I ACQUIRED THE ACFT VISUALLY LESS THAN A MI AWAY AND HAD JUST ENOUGH TIME TO ROLL THE ACFT BACK TO THE R BEFORE PASSING LESS THAN 100 YDS LATERALLY AND AROUND 500 VERTLY. I BELIEVE WE GOT DOWN TO 26500 FT ALTHOUGH THE FE THOUGHT IT WAS 25500 FT. WHEN I ADVISED ATC OF OUR ALT, HE WAS ALARMED AND WANTED TO KNOW WHY WE WERE NOT AT FL280. I ADVISED HIM OF OUR TCASII 'RA' AND AFTER ASKING WHAT ALT HE WANTED US TO RETURN TO, HE SAID FL270 AND NO OTHER COMMENTS WERE MADE. I'M A FIRM BELIEVER IN TCASII. IF YOU FOLLOW IT, IT WILL KEEP YOU CLR OF THE INTRUDING ACFT. IT'S REAL HARD TO SUDDENLY PUNCH OFF THE AUTOPLT AND DEVIATE FROM YOUR ASSIGNED ALT WITHOUT A CLRNC BUT THERE IS REALLY NO OTHER WAY TO DO IT. IF YOU WIND UP DIVING DOWN ON ANOTHER ACFT YOU HAVE TO TRUST THAT TCASII WILL KEEP YOU CLR BUT ONLY IF EVERYBODY FOLLOWS THEIR TCASII INSTRUCTIONS, I SUSPECT THAT WE HAD TO DEVIATE SO FAR FROM OUR ASSIGNED ALT WAS BECAUSE THE INTRUDING ACFT EITHER DID NOT HAVE TCASII ON BOARD OR THAT THE CREW OF THE OTHER ACFT FOLLOWED ATC'S INSTRUCTIONS TO DSND TO FL270 RATHER THAN FOLLOWING THEIR TCASII WHICH SHOULD HAVE BEEN INSTRUCTING THEM TO SHALLOW THEIR DSCNT OR EVEN CLB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THE CTLR DID NOT ISSUE TFC OR THE REASON FOR THE RADAR VECTOR OFF COURSE. TCASII WAS REDUCED FROM 40 MI RANGE TO 5 MI RANGE. RPTR STATED NO ADVISORY WAS GIVEN TO ATC THAT THEY WERE RESPONDING TO AN RA UNTIL AFTER THE INCIDENT. FLC ATC REVIEW FACILITY SUPVR SAID AN OPERATIONAL ERROR WAS BEING FILED. RPTR DID NOT KNOW IF ACR CL60 HAD TCASII OR RESPONDED TO TCASII.

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.