Narrative:

The problem herein described arose because our TCASII system interrogated an oncoming transponder on an aircraft that was climbing to a cruise altitude 1000 ft below ours. While the oncoming traffic was climbing, the lead computed by TCASII showed that that traffic would pass above us. We did not have visual contact until after we had begun a descent based on the TCASII RA to do so. We descended in compliance with the TCASII RA only 200 ft at which time we visually acquired the traffic which had just leveled at FL280 as planned for it. We immediately climbed back to FL290 and simultaneously the TCASII RA terminated. We breached the 1000 ft separation by 200 ft. A major contributor to this incident is the lead computing feature of TCASII which is based on the climb or descent. Flight guidance equipped aircraft should have the capability of using the selected altitude to input information to the transponder to show interrogating TCASII that they will have proper separation at level off. Supplemental information from acn 200444: contacted ft worth sector center per their request upon landing dfw. Captain stated that ft worth showed separation of 2 1/2 mi horizontal and approximately 600 ft vertical.

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Original NASA ASRS Text

Title: ACR MLG ALTDEV EXCURSION FROM CLRNC IN RESPONSE TO TCASII TA AT CRS ALT.

Narrative: THE PROBLEM HEREIN DESCRIBED AROSE BECAUSE OUR TCASII SYS INTERROGATED AN ONCOMING TRANSPONDER ON AN ACFT THAT WAS CLBING TO A CRUISE ALT 1000 FT BELOW OURS. WHILE THE ONCOMING TFC WAS CLBING, THE LEAD COMPUTED BY TCASII SHOWED THAT THAT TFC WOULD PASS ABOVE US. WE DID NOT HAVE VISUAL CONTACT UNTIL AFTER WE HAD BEGUN A DSCNT BASED ON THE TCASII RA TO DO SO. WE DSNDED IN COMPLIANCE WITH THE TCASII RA ONLY 200 FT AT WHICH TIME WE VISUALLY ACQUIRED THE TFC WHICH HAD JUST LEVELED AT FL280 AS PLANNED FOR IT. WE IMMEDIATELY CLBED BACK TO FL290 AND SIMULTANEOUSLY THE TCASII RA TERMINATED. WE BREACHED THE 1000 FT SEPARATION BY 200 FT. A MAJOR CONTRIBUTOR TO THIS INCIDENT IS THE LEAD COMPUTING FEATURE OF TCASII WHICH IS BASED ON THE CLB OR DSCNT. FLT GUIDANCE EQUIPPED ACFT SHOULD HAVE THE CAPABILITY OF USING THE SELECTED ALT TO INPUT INFO TO THE TRANSPONDER TO SHOW INTERROGATING TCASII THAT THEY WILL HAVE PROPER SEPARATION AT LEVEL OFF. SUPPLEMENTAL INFO FROM ACN 200444: CONTACTED FT WORTH SECTOR CTR PER THEIR REQUEST UPON LNDG DFW. CAPT STATED THAT FT WORTH SHOWED SEPARATION OF 2 1/2 MI HORIZ AND APPROX 600 FT VERT.

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.