Narrative:

While en route level at FL290 were given a frequency change (handoff). Before new frequency was selected we received a TA 'traffic, traffic' from TCASII. Target was 12 O'clock, 5 mi, maximum range of display. Almost immediately thereafter, received RA 'climb, climb.' traffic was in sight, closing. TCASII showed traffic 1000 ft -- that is, 1000 ft below. I disengaged autoplt and started a slow climb. TCASII then annunciated 'monitor vertical speed.' we climbed approximately 500 ft over assigned altitude of FL290 as traffic passed clear. Descended back to FL290 and checked in with the new controller. After reporting level, we explained the brief altitude change. Controller said he observed climb and asked if the TCASII warning was caused by the traffic 1000 ft below which had just passed. I said that must have been the cause. After the traffic passed, TCASII annunciated, 'clear of conflict,' but there never was a conflict. Although we had traffic in sight, altitude of other aircraft at altitude and high closure rates, is hard to judge visually and I decided a small climb to comply with TCASII was safest. The TCASII worked fine throughout remainder of flight, but we wrote it up for maintenance.

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Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION WHEN FLC RECEIVES A TCASII RA ON OPPOSITE DIRECTION TFC.

Narrative: WHILE ENRTE LEVEL AT FL290 WERE GIVEN A FREQ CHANGE (HDOF). BEFORE NEW FREQ WAS SELECTED WE RECEIVED A TA 'TFC, TFC' FROM TCASII. TARGET WAS 12 O'CLOCK, 5 MI, MAX RANGE OF DISPLAY. ALMOST IMMEDIATELY THEREAFTER, RECEIVED RA 'CLB, CLB.' TFC WAS IN SIGHT, CLOSING. TCASII SHOWED TFC 1000 FT -- THAT IS, 1000 FT BELOW. I DISENGAGED AUTOPLT AND STARTED A SLOW CLB. TCASII THEN ANNUNCIATED 'MONITOR VERT SPD.' WE CLBED APPROX 500 FT OVER ASSIGNED ALT OF FL290 AS TFC PASSED CLR. DSNDED BACK TO FL290 AND CHKED IN WITH THE NEW CTLR. AFTER RPTING LEVEL, WE EXPLAINED THE BRIEF ALT CHANGE. CTLR SAID HE OBSERVED CLB AND ASKED IF THE TCASII WARNING WAS CAUSED BY THE TFC 1000 FT BELOW WHICH HAD JUST PASSED. I SAID THAT MUST HAVE BEEN THE CAUSE. AFTER THE TFC PASSED, TCASII ANNUNCIATED, 'CLR OF CONFLICT,' BUT THERE NEVER WAS A CONFLICT. ALTHOUGH WE HAD TFC IN SIGHT, ALT OF OTHER ACFT AT ALT AND HIGH CLOSURE RATES, IS HARD TO JUDGE VISUALLY AND I DECIDED A SMALL CLB TO COMPLY WITH TCASII WAS SAFEST. THE TCASII WORKED FINE THROUGHOUT REMAINDER OF FLT, BUT WE WROTE IT UP FOR MAINT.

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.