Narrative:

Cleared to descend from 12000 ft MSL to a lower altitude, approaching 11500 ft I noticed an airplane below and to my left which appeared like it would become a conflict. A brief discussion with the non-flying pilot and we decided to climb back up to 12000 ft. At same time we started the climb, TCASII gave us a monitor vertical speed followed by a climb RA. Shortly thereafter approach control gave other aircraft a lower altitude and also gave us a lower altitude. Remainder of flight uneventful. TCASII worked as it should have.

Google
 

Original NASA ASRS Text

Title: LTSS BTWN ACR MLG AND AN UNKNOWN ACFT.

Narrative: CLRED TO DSND FROM 12000 FT MSL TO A LOWER ALT, APCHING 11500 FT I NOTICED AN AIRPLANE BELOW AND TO MY L WHICH APPEARED LIKE IT WOULD BECOME A CONFLICT. A BRIEF DISCUSSION WITH THE NON-FLYING PLT AND WE DECIDED TO CLB BACK UP TO 12000 FT. AT SAME TIME WE STARTED THE CLB, TCASII GAVE US A MONITOR VERT SPD FOLLOWED BY A CLB RA. SHORTLY THEREAFTER APCH CTL GAVE OTHER ACFT A LOWER ALT AND ALSO GAVE US A LOWER ALT. REMAINDER OF FLT UNEVENTFUL. TCASII WORKED AS IT SHOULD HAVE.

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.