Narrative:

Flight aa on jun/xx/97 from yyc to slc. I was the first officer flying at the time. We were about 20 mi from slc with approach control at 13000 ft level, IMC/IFR. We received a TCASII RA commanding an immediate 'descend' with a green arc on the vvi of minimum 3500 FPM down. At the same time, there was a display of a target +01 (in red) directly above us. The captain concurred and I began the descent. The captain then radioed ATC and told them of our descent due to a TCASII RA command. ATC did not respond immediately. We broke out of the WX at about 12300 ft to see a cessna caravan to our right almost co-altitude. We were on a parallel course, collision was not a factor. At this time, ATC finally asked us if we had the traffic. We said yes, and ATC told us to climb back to 13000 ft. The caravan acknowledged seeing us. Prior to receiving the TCASII RA command, there was no early 'traffic' warning. ATC showed no other aircraft in our vicinity. Either there was a TCASII malfunction, or ATC did not pick up the traffic causing our TCASII RA. Callback conversation with reporter revealed the following information: reporter stated that during the descent they were surprised at how rapidly the TCASII 'RA,' with no 'TA' went from plus 3, 2, 1 on target, to 'descend, descend, descend.' the flight crew made the descent but as the descent continued through the cleared altitude, they broke out of the clouds just in time to see a cessna caravan some 500 ft away. There was no TCASII RA for this aircraft. The caravan saw the B727 descend into his altitude and made the comment to slc TRACON, 'nice going, salt lake.' the reporter's aircraft climbed back up to the assigned altitude. No evasive action was taken by either aircraft. Upon landing, the flight crew talked with TRACON and learned that TRACON never had a target in the area when they got the TCASII RA to cause the initial descent. TRACON did have the caravan target at all times. Maintenance informed the reporter that they took the TCASII unit out for inspection and the caravan had its transponder inspected. No specific results of any equipment faults were mentioned to the reporter. Supplemental information from acn 370796: the vsi's simultaneously commanded about a 3500 FPM descent, and the TCASII RA/WX display showed a red target almost coincidental with our position, and 300 ft above (+3) and descending! As the display went from '+2' to '+1' I commanded the copilot, who was flying the aircraft, to begin a descent and simultaneously informed approach control that we were descending in response to a TCASII RA command. We descended to approximately 11800 ft. During the descent, the so saw the red RA disappear and a yellow target appear accompanied with a 'monitor vertical speed' announcement. The caravan pilot also transmitted his displeasure with the incident, reporting the separation at '70-80 yards.' supplemental information from acn 370819: we descended approximately 1100 ft. During the descent the red RA disappeared and a yellow target (with no relative altitude) appeared along with a 'monitor vertical speed' announcement. Towards the bottom of our descent we emerged from the clouds and immediately saw a cessna caravan at our altitude about 1000 ft off our right wing. The PNF called the traffic to ATC and restated our RA commanded descent. The cessna also called ATC and stated the separation as 70-80 yards. By this time we had passed the cessna and ATC directed us to climb back to 13000 ft. We called RAPCON after landing and they stated the cessna had been level at 12000 ft for 20 mi.

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Original NASA ASRS Text

Title: A B727 DSNDING INTO SLC RECEIVES A TCASII RA AND IMMEDIATELY INCREASES HIS RATE OF DSCNT. AS THE B727 DSNDS IT COMES CLOSE TO A CESSNA CARAVAN. THE CARAVAN COMPLAINS OF THE CLOSE PROX OF THE DSNDING B727. RELIABILITY OF TCASII IS IN QUESTION DURING THIS INCIDENT.

Narrative: FLT AA ON JUN/XX/97 FROM YYC TO SLC. I WAS THE FO FLYING AT THE TIME. WE WERE ABOUT 20 MI FROM SLC WITH APCH CTL AT 13000 FT LEVEL, IMC/IFR. WE RECEIVED A TCASII RA COMMANDING AN IMMEDIATE 'DSND' WITH A GREEN ARC ON THE VVI OF MINIMUM 3500 FPM DOWN. AT THE SAME TIME, THERE WAS A DISPLAY OF A TARGET +01 (IN RED) DIRECTLY ABOVE US. THE CAPT CONCURRED AND I BEGAN THE DSCNT. THE CAPT THEN RADIOED ATC AND TOLD THEM OF OUR DSCNT DUE TO A TCASII RA COMMAND. ATC DID NOT RESPOND IMMEDIATELY. WE BROKE OUT OF THE WX AT ABOUT 12300 FT TO SEE A CESSNA CARAVAN TO OUR R ALMOST CO-ALT. WE WERE ON A PARALLEL COURSE, COLLISION WAS NOT A FACTOR. AT THIS TIME, ATC FINALLY ASKED US IF WE HAD THE TFC. WE SAID YES, AND ATC TOLD US TO CLB BACK TO 13000 FT. THE CARAVAN ACKNOWLEDGED SEEING US. PRIOR TO RECEIVING THE TCASII RA COMMAND, THERE WAS NO EARLY 'TFC' WARNING. ATC SHOWED NO OTHER ACFT IN OUR VICINITY. EITHER THERE WAS A TCASII MALFUNCTION, OR ATC DID NOT PICK UP THE TFC CAUSING OUR TCASII RA. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT DURING THE DSCNT THEY WERE SURPRISED AT HOW RAPIDLY THE TCASII 'RA,' WITH NO 'TA' WENT FROM PLUS 3, 2, 1 ON TARGET, TO 'DSND, DSND, DSND.' THE FLC MADE THE DSCNT BUT AS THE DSCNT CONTINUED THROUGH THE CLRED ALT, THEY BROKE OUT OF THE CLOUDS JUST IN TIME TO SEE A CESSNA CARAVAN SOME 500 FT AWAY. THERE WAS NO TCASII RA FOR THIS ACFT. THE CARAVAN SAW THE B727 DSND INTO HIS ALT AND MADE THE COMMENT TO SLC TRACON, 'NICE GOING, SALT LAKE.' THE RPTR'S ACFT CLBED BACK UP TO THE ASSIGNED ALT. NO EVASIVE ACTION WAS TAKEN BY EITHER ACFT. UPON LNDG, THE FLC TALKED WITH TRACON AND LEARNED THAT TRACON NEVER HAD A TARGET IN THE AREA WHEN THEY GOT THE TCASII RA TO CAUSE THE INITIAL DSCNT. TRACON DID HAVE THE CARAVAN TARGET AT ALL TIMES. MAINT INFORMED THE RPTR THAT THEY TOOK THE TCASII UNIT OUT FOR INSPECTION AND THE CARAVAN HAD ITS XPONDER INSPECTED. NO SPECIFIC RESULTS OF ANY EQUIP FAULTS WERE MENTIONED TO THE RPTR. SUPPLEMENTAL INFO FROM ACN 370796: THE VSI'S SIMULTANEOUSLY COMMANDED ABOUT A 3500 FPM DSCNT, AND THE TCASII RA/WX DISPLAY SHOWED A RED TARGET ALMOST COINCIDENTAL WITH OUR POS, AND 300 FT ABOVE (+3) AND DSNDING! AS THE DISPLAY WENT FROM '+2' TO '+1' I COMMANDED THE COPLT, WHO WAS FLYING THE ACFT, TO BEGIN A DSCNT AND SIMULTANEOUSLY INFORMED APCH CTL THAT WE WERE DSNDING IN RESPONSE TO A TCASII RA COMMAND. WE DSNDED TO APPROX 11800 FT. DURING THE DSCNT, THE SO SAW THE RED RA DISAPPEAR AND A YELLOW TARGET APPEAR ACCOMPANIED WITH A 'MONITOR VERT SPD' ANNOUNCEMENT. THE CARAVAN PLT ALSO XMITTED HIS DISPLEASURE WITH THE INCIDENT, RPTING THE SEPARATION AT '70-80 YARDS.' SUPPLEMENTAL INFO FROM ACN 370819: WE DSNDED APPROX 1100 FT. DURING THE DSCNT THE RED RA DISAPPEARED AND A YELLOW TARGET (WITH NO RELATIVE ALT) APPEARED ALONG WITH A 'MONITOR VERT SPD' ANNOUNCEMENT. TOWARDS THE BOTTOM OF OUR DSCNT WE EMERGED FROM THE CLOUDS AND IMMEDIATELY SAW A CESSNA CARAVAN AT OUR ALT ABOUT 1000 FT OFF OUR R WING. THE PNF CALLED THE TFC TO ATC AND RESTATED OUR RA COMMANDED DSCNT. THE CESSNA ALSO CALLED ATC AND STATED THE SEPARATION AS 70-80 YARDS. BY THIS TIME WE HAD PASSED THE CESSNA AND ATC DIRECTED US TO CLB BACK TO 13000 FT. WE CALLED RAPCON AFTER LNDG AND THEY STATED THE CESSNA HAD BEEN LEVEL AT 12000 FT FOR 20 MI.

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.