Narrative:

While climbing through 15000 ft, got a TCASII RA 'reduce climb,' followed by 'descend, descend,' followed by 'increase descent,' followed by 'monitor vertical speed,' followed by 'clear of conflict.' we complied with all the RA's. I immediately told ATC what was happening, and they advised me that there was no traffic in the vicinity. We started climbing again, and a couple of mins later, had the same TCASII displays and RA's commands as described above. We once again complied with RA's and advised ATC that we were descending, because of the RA's. ATC said they had no traffic in the vicinity. At this point, we were not sure what was happening, but suspected something wrong with the TCASII. At no time, however, did we have a TCASII inoperative displayed, nor did we have a traffic symbol or target aircraft displayed on the TCASII. The first officer and I discussed what was happening, and we agreed that there must be something wrong with our equipment. A couple of mins later, the TCASII RA went off again with the same scenario, but this time we disregarded, talked again to ATC, and once again was told that there was no traffic in the area. We proceeded to our destination, landed uneventfully and wrote the TCASII up in the logbook. The fact that no target aircraft was displayed, therefore, giving us no hint of where to look for conflicting traffic, and the urgency of the RA commands created a situation where you had to act now, follow the RA commands now, and later analyze what you had. Not until we had gone through 2 full cycles of RA's, taking action, and being cleared by ATC, did we consider that we may have a faulty TCASII.

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Original NASA ASRS Text

Title: DC9-30 CREW HAD TCASII RA'S FROM A MALFUNCTIONING TCASII SYS.

Narrative: WHILE CLBING THROUGH 15000 FT, GOT A TCASII RA 'REDUCE CLB,' FOLLOWED BY 'DSND, DSND,' FOLLOWED BY 'INCREASE DSCNT,' FOLLOWED BY 'MONITOR VERT SPD,' FOLLOWED BY 'CLR OF CONFLICT.' WE COMPLIED WITH ALL THE RA'S. I IMMEDIATELY TOLD ATC WHAT WAS HAPPENING, AND THEY ADVISED ME THAT THERE WAS NO TFC IN THE VICINITY. WE STARTED CLBING AGAIN, AND A COUPLE OF MINS LATER, HAD THE SAME TCASII DISPLAYS AND RA'S COMMANDS AS DESCRIBED ABOVE. WE ONCE AGAIN COMPLIED WITH RA'S AND ADVISED ATC THAT WE WERE DSNDING, BECAUSE OF THE RA'S. ATC SAID THEY HAD NO TFC IN THE VICINITY. AT THIS POINT, WE WERE NOT SURE WHAT WAS HAPPENING, BUT SUSPECTED SOMETHING WRONG WITH THE TCASII. AT NO TIME, HOWEVER, DID WE HAVE A TCASII INOP DISPLAYED, NOR DID WE HAVE A TFC SYMBOL OR TARGET ACFT DISPLAYED ON THE TCASII. THE FO AND I DISCUSSED WHAT WAS HAPPENING, AND WE AGREED THAT THERE MUST BE SOMETHING WRONG WITH OUR EQUIP. A COUPLE OF MINS LATER, THE TCASII RA WENT OFF AGAIN WITH THE SAME SCENARIO, BUT THIS TIME WE DISREGARDED, TALKED AGAIN TO ATC, AND ONCE AGAIN WAS TOLD THAT THERE WAS NO TFC IN THE AREA. WE PROCEEDED TO OUR DEST, LANDED UNEVENTFULLY AND WROTE THE TCASII UP IN THE LOGBOOK. THE FACT THAT NO TARGET ACFT WAS DISPLAYED, THEREFORE, GIVING US NO HINT OF WHERE TO LOOK FOR CONFLICTING TFC, AND THE URGENCY OF THE RA COMMANDS CREATED A SIT WHERE YOU HAD TO ACT NOW, FOLLOW THE RA COMMANDS NOW, AND LATER ANALYZE WHAT YOU HAD. NOT UNTIL WE HAD GONE THROUGH 2 FULL CYCLES OF RA'S, TAKING ACTION, AND BEING CLRED BY ATC, DID WE CONSIDER THAT WE MAY HAVE A FAULTY 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.