Narrative:

This was the descent phase of our flight heading sse for a landing at cdn. We were working clt approach and had been assigned 14000 ft because of another air carrier at 10 O'clock position, 13000 ft, 15 NM, that was also descending for a landing at clt. Our courses were converging. We established visual contact with the other aircraft and reported this to clt approach, who then cleared us to descend to 11000 ft with visual reference to the other aircraft. Clt also advised the other aircraft of our descent which was acknowledged by them. The captain descended quickly below the other aircraft to 11000 ft and leveled there. I do not know whether the other aircraft was cleared to continue its descent, but I observed on the TCASII that it was continuing to descend through 12000 ft, and by now our horizontal separation was 7 mi on a converging course. I advised the captain that we needed to take action, however, he seemed unsure of just what to do. I observed that the other aircraft had stopped the descent approximately 500 ft above us. The TCASII sounded a TA, followed by an RA to descend. At this point, the TCASII showed 500 ft vertical, and 4 mi horizontal separation. The captain disconnected the autoplt to comply with the RA. As I was reaching for the microphone to report a TCASII descent, clt reclred us to descend to 3000 ft, which was executed immediately. The other aircraft passed overhead at approximately 1000 ft. This situation presented some practical dilemmas, which contributed to the difficulty in making a timely decision: ('boxed in'). 1) turning left would only increase our closure rate, aggravating the situation. (Other aircraft at 10 O'clock position, 7 M8.) 2) turning right would put the other aircraft out of our sight, compromising reference based on visual separation. 3) the other aircraft was above us, so climbing would only decrease separation. 4) we had descended to our cleared altitude (11000 ft) so a descent was not technically allowed until the TCASII RA sounded. 5) the other aircraft had stopped its descent. I have long felt that IFR clrncs based on visual separation at night are not wise. It is more difficult to judge one's relative position to other aircraft at night. And though not the case in this instance, the chances of fixing on the wrong aircraft increase at night. This incident further confirms my belief that maneuvers based on visual separation should not be permitted at night for aircraft under IFR control. Clt approach did not indicate before hand or comment after, but I believe they were expecting us to descend visually above the other aircraft.

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Original NASA ASRS Text

Title: AFTER ACCEPTING VISUAL SEPARATION, FA20 FLC CONSIDERS OPTIONS SEEING VERT AND LATERAL DISTANCES DECREASE FROM THE OTHER ACFT, TAKING ACTION ONLY WHEN TCASII ALERTS.

Narrative: THIS WAS THE DSCNT PHASE OF OUR FLT HDG SSE FOR A LNDG AT CDN. WE WERE WORKING CLT APCH AND HAD BEEN ASSIGNED 14000 FT BECAUSE OF ANOTHER ACR AT 10 O'CLOCK POS, 13000 FT, 15 NM, THAT WAS ALSO DSNDING FOR A LNDG AT CLT. OUR COURSES WERE CONVERGING. WE ESTABLISHED VISUAL CONTACT WITH THE OTHER ACFT AND RPTED THIS TO CLT APCH, WHO THEN CLRED US TO DSND TO 11000 FT WITH VISUAL REF TO THE OTHER ACFT. CLT ALSO ADVISED THE OTHER ACFT OF OUR DSCNT WHICH WAS ACKNOWLEDGED BY THEM. THE CAPT DSNDED QUICKLY BELOW THE OTHER ACFT TO 11000 FT AND LEVELED THERE. I DO NOT KNOW WHETHER THE OTHER ACFT WAS CLRED TO CONTINUE ITS DSCNT, BUT I OBSERVED ON THE TCASII THAT IT WAS CONTINUING TO DSND THROUGH 12000 FT, AND BY NOW OUR HORIZ SEPARATION WAS 7 MI ON A CONVERGING COURSE. I ADVISED THE CAPT THAT WE NEEDED TO TAKE ACTION, HOWEVER, HE SEEMED UNSURE OF JUST WHAT TO DO. I OBSERVED THAT THE OTHER ACFT HAD STOPPED THE DSCNT APPROX 500 FT ABOVE US. THE TCASII SOUNDED A TA, FOLLOWED BY AN RA TO DSND. AT THIS POINT, THE TCASII SHOWED 500 FT VERT, AND 4 MI HORIZ SEPARATION. THE CAPT DISCONNECTED THE AUTOPLT TO COMPLY WITH THE RA. AS I WAS REACHING FOR THE MIKE TO RPT A TCASII DSCNT, CLT RECLRED US TO DSND TO 3000 FT, WHICH WAS EXECUTED IMMEDIATELY. THE OTHER ACFT PASSED OVERHEAD AT APPROX 1000 FT. THIS SIT PRESENTED SOME PRACTICAL DILEMMAS, WHICH CONTRIBUTED TO THE DIFFICULTY IN MAKING A TIMELY DECISION: ('BOXED IN'). 1) TURNING L WOULD ONLY INCREASE OUR CLOSURE RATE, AGGRAVATING THE SIT. (OTHER ACFT AT 10 O'CLOCK POS, 7 M8.) 2) TURNING R WOULD PUT THE OTHER ACFT OUT OF OUR SIGHT, COMPROMISING REF BASED ON VISUAL SEPARATION. 3) THE OTHER ACFT WAS ABOVE US, SO CLBING WOULD ONLY DECREASE SEPARATION. 4) WE HAD DSNDED TO OUR CLRED ALT (11000 FT) SO A DSCNT WAS NOT TECHNICALLY ALLOWED UNTIL THE TCASII RA SOUNDED. 5) THE OTHER ACFT HAD STOPPED ITS DSCNT. I HAVE LONG FELT THAT IFR CLRNCS BASED ON VISUAL SEPARATION AT NIGHT ARE NOT WISE. IT IS MORE DIFFICULT TO JUDGE ONE'S RELATIVE POS TO OTHER ACFT AT NIGHT. AND THOUGH NOT THE CASE IN THIS INSTANCE, THE CHANCES OF FIXING ON THE WRONG ACFT INCREASE AT NIGHT. THIS INCIDENT FURTHER CONFIRMS MY BELIEF THAT MANEUVERS BASED ON VISUAL SEPARATION SHOULD NOT BE PERMITTED AT NIGHT FOR ACFT UNDER IFR CTL. CLT APCH DID NOT INDICATE BEFORE HAND OR COMMENT AFTER, BUT I BELIEVE THEY WERE EXPECTING US TO DSND VISUALLY ABOVE THE OTHER ACFT.

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.