Narrative:

At 5000 ft MSL approximately 10 NM northwest of korf while being vectored for a visual approach to runway 05 we were advised of an small aircraft, traffic at 1 O'clock approximately 5 NM. Traffic was in contact with approach and was at 4500 ft MSL maneuvering. We visually acquired traffic at approximately 1230 and 2 mi. It appeared level at about 4500 ft MSL. TCAS had given us a 'traffic, traffic' advisory (TA) which helped us establish the visual. When traffic was at about 1230 and 2 NM, it started a left hand turn into us about 500 ft below our altitude. The traffic disappeared underneath glareshield and nose of aircraft. At same time contact was lost, TCAS provided a RA. It directed a 'climb, climb'. Green ivsi indications directed an approximately 1200 ft vertical climb rate. I complied with this until receiving the 'monitor' announcement followed shortly later by a 'clear of conflict' notice. Actual climb was from 5000 ft MSL to 5400 ft MSL. We advised ATC of our TCAS RA and altitude deviation. Controller advised us that traffic had legal separation. I complied with TCAS RA because I had lost visual contact with traffic and we are required to follow it's direction. Supplemental information from acn 184368. We simply could not tell if he was climbing, or not. TCAS was a positive factor in this incident. In addition, when we advised approach control that we were receiving a RA and would be climbing out of our assigned altitude, they did not question us and were courteous and helpful in their handling of this event.

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Original NASA ASRS Text

Title: TCASII RA CAUSES ACR PIC TO EXECUTE AN EVASIVE ACTION CLB AND RESULTS IN AN ALT DEV ALT EXCURSION.

Narrative: AT 5000 FT MSL APPROX 10 NM NW OF KORF WHILE BEING VECTORED FOR A VISUAL APCH TO RWY 05 WE WERE ADVISED OF AN SMA, TFC AT 1 O'CLOCK APPROX 5 NM. TFC WAS IN CONTACT WITH APCH AND WAS AT 4500 FT MSL MANEUVERING. WE VISUALLY ACQUIRED TFC AT APPROX 1230 AND 2 MI. IT APPEARED LEVEL AT ABOUT 4500 FT MSL. TCAS HAD GIVEN US A 'TFC, TFC' ADVISORY (TA) WHICH HELPED US ESTABLISH THE VISUAL. WHEN TFC WAS AT ABOUT 1230 AND 2 NM, IT STARTED A L HAND TURN INTO US ABOUT 500 FT BELOW OUR ALT. THE TFC DISAPPEARED UNDERNEATH GLARESHIELD AND NOSE OF ACFT. AT SAME TIME CONTACT WAS LOST, TCAS PROVIDED A RA. IT DIRECTED A 'CLB, CLB'. GREEN IVSI INDICATIONS DIRECTED AN APPROX 1200 FT VERT CLB RATE. I COMPLIED WITH THIS UNTIL RECEIVING THE 'MONITOR' ANNOUNCEMENT FOLLOWED SHORTLY LATER BY A 'CLR OF CONFLICT' NOTICE. ACTUAL CLB WAS FROM 5000 FT MSL TO 5400 FT MSL. WE ADVISED ATC OF OUR TCAS RA AND ALT DEV. CTLR ADVISED US THAT TFC HAD LEGAL SEPARATION. I COMPLIED WITH TCAS RA BECAUSE I HAD LOST VISUAL CONTACT WITH TFC AND WE ARE REQUIRED TO FOLLOW IT'S DIRECTION. SUPPLEMENTAL INFO FROM ACN 184368. WE SIMPLY COULD NOT TELL IF HE WAS CLBING, OR NOT. TCAS WAS A POSITIVE FACTOR IN THIS INCIDENT. IN ADDITION, WHEN WE ADVISED APCH CTL THAT WE WERE RECEIVING A RA AND WOULD BE CLBING OUT OF OUR ASSIGNED ALT, THEY DID NOT QUESTION US AND WERE COURTEOUS AND HELPFUL IN THEIR HANDLING OF THIS EVENT.

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.