AFTER SEAT SWAP; ONCOMING FO OBSERVES THAT TCASII WAS NOT DISPLAYING; ADJUSTS EQUIP FOR OPERATIONAL USE; AND OBSERVES ANOTHER ACFT 4 MI IN TRAIL. ZAN THOUGHT TFC WAS 10 MINS IN TRAIL AND DSNDS ACR FROM FL350 TO FL340.

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AFTER SEAT SWAP DURING CRUISE; OTHER COPLT NOTICED OUR TFC BUTTONS WERE NOT PUSHED TO DISPLAY TCASII INTO OUR CRT'S. ONCE PUSHED; THERE WAS A TARGET AT OUR ALT OF FL350; 4 MI BEHIND US. WE CALLED ON GUARD TO FIND WHO IT WAS. ACR SAID IT WAS THEM. DURING THIS; WE TALKED TO ANCHORAGE ON 119.1 AND THEY DSNDED US TO FL340. ANCHORAGE SAID HE WAS TOLD ON HF THAT THERE WAS A 10 MIN SEPARATION BTWN US. IN REALITY; THERE WAS ABOUT 1 MIN. I'M NOT SURE WHERE THE BREAKDOWN WAS WITH ATC; AIR CREW; ETC. SUPPLEMENTAL INFO FROM ACN 517232: ON TAKING POS AFTER CREW SWAP (WE WERE BUNKIES TAKING OVER); I NOTICED TCASII WAS NOT SELECTED ON PFD'S. UPON SELECTING TFC DISPLAY; I NOTICED A TCASII TARGET CO-ALT AND 4 MI IN TRAIL AT FL350. USING 123.45; FOUND OUT IT WAS ACR. CALLED ZAN ON 119.1 TO INQUIRE. WE WERE NOT RADAR CONTACT YET. THEY IMMEDIATELY GAVE US DSCNT TO FL340. WE WERE CLBED VIA CPDLC APPROX XA45Z TO FL350 (WHILE BUNKIES WERE ON REST BREAK). IT WAS VMC AT NIGHT. ACR WAS AT FL350 PRIOR TO OUR CLB. ZAN SAID HE WAS TOLD THERE WAS 10 MIN SEPARATION BTWN ACFT (I DON'T KNOW WHO TOLD THEM THAT).