ACR X TCASII RA HAD LTSS FROM Y. SYS ERROR.

Narrative

ACR X AT FL295 WHILE DSNDING FROM FL330 TO FL290 ASSIGNED. AT 290 KIAS (56 MI SW MOL) WE EXPERIENCED A TCASII RA EVENT. WE WERE TALKING TO ZDC ON 133.02 ON AN APPROVED WX DEV BTWN CUMULO NIMBUS WITH GOOD INFLT VISIBILITY WHEN WE OBSERVED A YELLOW TFC SYMBOL ON TCASII DISPLAY AT APPROX 1 O'CLOCK POS; 6 MI; PLUS 100 FT ABOVE OUR ALT. ZDC THEN CALLED THAT TFC TO US AND ORDERED AN IMMEDIATE DSCNT TO FL250. PF (CAPT) DISCONNECTED THE AUTOPLT AND INITIATED AN IMMEDIATE DSCNT WHILE I VISUALLY SEARCHED FOR TFC. WE RECEIVED A TCASII RA TO 'CLB; XING CLB' WITH A COMMANDED (PLUS 2500 FPM CLB) WHEN ALREADY ESTABLISHED IN THE DSCNT; SO WE CONTINUED TO DSND. THE DSCNT RATE BECAME APPROX 4000 FPM. THE ALT DIFFERENCE OF ACFT Y INDICATED ON THE TCASII DISPLAY WENT FROM PLUS 100 FT TO PLUS 900 FT DURING THE MANEUVER AND NEVER SHOWED LEVEL WITH US. THE TFC PAST DIRECTLY IN FRONT OF US AND THEN CONTINUED OVER TO OUR 9 O'CLOCK POS AT ABOUT 2 MI; PLUS 900 FT ON TCASII DISPLAY. WE NEVER VISUALLY SPOTTED THE TFC WHEN THE 'CLR OF CONFLICT' WAS ANNOUNCED BY TCASII. THE ENTIRE EVEN LASTED ABOUT 30 SECONDS. WE SHALLOWED THE DSCNT RATE AND LEVELED AT FL250 ASSIGNED. WE NEVER HEARD ANY OTHER INSTRUCTIONS OR KNEW WHO THE OTHER ACFT WAS.