LTT ACR HAS TCASII RA DURING CLB. RESPONDS.

Narrative

FLT DEPARTED RWY 34 AT BGM. AFTER DEP WE WERE GIVEN A L TURN TO 180 DEGS DIRECT AVP WHEN ABLE. UPON ROLLING OUT ON 180 DEG HDG; WE RECEIVED A TA BY TCASII FOR TFC AT 11 O'CLOCK AND 1300 FT BELOW OUR ALT. THE TA THEN BECAME A 'DSND; XING DSND' RA APPROX 5 SECONDS LATER. I; THE CAPT; WAS FLYING AND INITIATED THE COMMANDED 1500 FPM DSCNT. WHEN THE RA WAS INITIALLY RECEIVED WE WERE AT 3400 MSL AND APPROX 2000 FT AGL. ONCE ESTABLISHED IN THE DSCNT THE RA BECAME A BLUE PROX TARGET AT 10 O'CLOCK AND 1200 FT BELOW OUR ALT. THE TARGET THEN MOVED RAPIDLY OFF TO OUR L REAR AND DISAPPEARED FROM TCASII. A NORMAL CLB WAS RESUMED AND ATC WAS ADVISED. ATC STATED THE ONLY TFC THEY HAD WAS A DEP OFF RWY 34 AT BGM AND WAS APPROX 5 MI AT OUR 7 O'CLOCK POS. I BELIEVE THAT THE RA WAS IN RESPONSE TO THE ACFT DEPARTING BGM RWY 34 WHICH WAS AN ACFT WHICH HAS A RAPID CLB RATE. OUR ACFT WAS JUST ROLLING OUT OF A 20 DEG L BANK WHICH MAY HAVE CONTRIBUTED TO THE LARGE AZIMUTH ERROR ON TCASII. THE TCASII SYS INSTALLED IN OUR ACFT OFTEN DISPLAYS RAPID AZIMUTH CHANGES.