Narrative:

During descent to 7000 ft MSL an aircraft appeared suddenly and with no prior history of TCASII recognition as a TA. It then turned to an RA calling for 'descend,' which I did. The conflict traffic passed at our altitude off the left wingtip. Myself and the captain believe the intruder aircraft turned their transponder on as they approached us, but that they had it turned off before that. The TCASII alert RA caused us to descend below our assigned altitude of 7000 ft MSL by approximately 700 ft. When we advised ATC we were at 6300 ft MSL and the TCASII RA problem, they said ok and assigned us a new altitude of 6000 ft MSL.

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Original NASA ASRS Text

Title: FK28 DSNDS THROUGH ASSIGNED ALT WHEN THEY RECEIVE A TCASII RA FROM A MOONEY WHOSE XPONDER HAD NOT BEEN EMITTING PRIOR TO THE RA. THE TCASII CALLED FOR 'DSND' AND CAUSED THE FK28 TO PASS THE MOONEY AT THE SAME ALT. IT DID NOT WORK AS ADVERTISED.

Narrative: DURING DSCNT TO 7000 FT MSL AN ACFT APPEARED SUDDENLY AND WITH NO PRIOR HISTORY OF TCASII RECOGNITION AS A TA. IT THEN TURNED TO AN RA CALLING FOR 'DSND,' WHICH I DID. THE CONFLICT TFC PASSED AT OUR ALT OFF THE L WINGTIP. MYSELF AND THE CAPT BELIEVE THE INTRUDER ACFT TURNED THEIR XPONDER ON AS THEY APCHED US, BUT THAT THEY HAD IT TURNED OFF BEFORE THAT. THE TCASII ALERT RA CAUSED US TO DSND BELOW OUR ASSIGNED ALT OF 7000 FT MSL BY APPROX 700 FT. WHEN WE ADVISED ATC WE WERE AT 6300 FT MSL AND THE TCASII RA PROB, THEY SAID OK AND ASSIGNED US A NEW ALT OF 6000 FT MSL.

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.